Fast Souring

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Comment faire un Sour Mash: Techniques du Fast Souring

Comme chaque brasseur en tout-grain le sait, le mash (maische ou maîche) est le mélange d'eau chaude et de grain. Un “Sour Mash” (mouture acide) est un moût qui contient des bactéries produisant de l'acide.


La plupart des gens associent le terme aux whiskies du sud des États-Unis. Mais cette technique peut également être utilisée pour le brassage. Un brasseur peut faire un petit Sour Mash pour abaisser le pH de son moût  lors du brassage d’une bière ordinaire ou il peut faire un Sour Mash important afin de brasser une bière de type acide .

Pratiquer un Sour Mash léger peut permettre d’abaisser le pH du moût et ne doit normalement pas affecter le goût plus que d’ajouter une petite quantité d'acide dans la bière finale mais en utilisant un Sour Mash plus important vous ajouterez un coté acidulé très net à votre bière.


Pour la plupart des bières, le pH à l’empâtage doit se situer entre 5.2 à 5.4. Mesurer le pH du moût est facile. Il suffit d’utiliser un ph mètre portatif numérique ou des bandelettes de test disponibles chez les fournisseurs pour le brassage amateur.


Si votre eau de brassage est faiblement carbonatée et assez riche en calcium, le pH du moût doit normalement s’ajuster de lui même de cette gamme de pH. Mais l'utilisation d’une eau avec des niveaux de carbonate élevés se traduira par un pH aussi plus élevé. Un pH supérieur à 5,6 peut diminuer l'efficacité d'extraction et permettre aux tanins d’être extraits dans le moût pendant le rinçage.
Il existe de nombreuses façons de réduire le pH du moût. La solution la plus simple consiste à ajouter de l'acide lactique, du sulfate de calcium (gypse) ou du chlorure de calcium. Le Sour Mash prend un peu plus de temps et d'efforts, mais il y a plein de motivations pour l'essayer. Le Sour Mash est une façon traditionnelle de faire baisser le pH et si vous êtes un puriste, il est conforme à la Reinheitsgebot. Certains brasseurs estiment qu'il est plus «naturel» que l'ajout direct d'acide mais il faut avant tout l’essayer car c’est tout simplement amusant et une excellente expérience brassicole.


Il y a aussi quelques inconvénients. Tout d'abord, cela nécessite plus de temps et d'énergie. Vous aurez besoin d'au moins deux jours pour produire suffisamment de bactéries lactique afin qu’elles soient correctement utilisées. Mais plus important encore il vous faudra redoubler de vigilance car  vous serez en train de produire activement des bactéries "nuisibles". Les Lactobacillus sont des contaminants indésirables dans presque tous les styles de bière mais qui ne sont néanmoins jamais pathogènes. Si vous nettoyer et stériliser votre équipement de brassage comme à l'accoutumé, vous ne devriez pas rencontrer de problèmes.
 

1/ Les Bases


Les Sour Mash sont une source d'acide lactique. L'acide est produit par les bactéries Lactobacillus. Le brasseur les introduit volontairement en ajoutant du malt directement ou via un starter et va leur permettre de se développer dans des conditions optimum de température (plus élevée), dans un récipient fermé pour éviter le contact avec l’oxygène pendant quelques jours. Ces conditions favorisent la croissance des Lactobacillus tout en inhibant la croissance d'autres organismes indésirables. Les Lactobacillus fermentent les sucres du malt et produisent, contrairement aux saccharomyces, de l'acide lactique.

Quelques termes techniques :

- Homofermentative signifie qu’une espère de Lactobacillus ne produit qu’un seul produit - dans notre cas l'acide lactique - quand elles fermentent. Les espèces hétéro-fermentaire d’autres genres de Lactobacillus produisent de l'acide acétique, de l'éthanol et du dioxyde de carbone, en plus de l'acide lactique pendant la fermentation. Elles peuvent aussi produire du diacétyle.

- Thermophile signifie aiment la chaleur; les Lactobacillus désirés dans les Sour Mash peuvent survivent à des températures aussi élevées que 55°C et se développent idéalement à des températures entre 35 à 50°C.

- anaérobie signifie sans oxygène; Les Lactobacillus peuvent vivre et se reproduire en l'absence d'oxygène.
Plusieurs espèces de Lactobacillus sont utilisés dans la fabrication de nombreux types d'aliments. Lactobacillus acidophilus et d'autres bactéries sont utilisées pour faire du yaourt. D'autres espèces de Lactobacillus sont utilisées dans la choucroute ou les cornichons.

2/ Choisir un processus

Il y a un certain nombre de types de brassage ou de recettes dans lesquels les brasseurs aimeraient ajouter un niveau correct et propre d’acidité lactique à leur bière dans un laps de temps assez court. Il est à la fois facile de travailler avec les Lactobacillus et ses bactéries sont facilement disponibles soit par des cultures de souches pures soit parce qu’elles sont naturellement présentes dans de nombreux malts de base. Afin d'atteindre cet objectif, plusieurs méthodes ont été développées pour permettre aux Lactobacillus de se multiplier et d’effectuer une fermentation acide de la mouture avant de passer à une fermentation standard aux Saccharomyces ou Brettanomyces

Un certain nombre de problèmes peuvent survenir lors de la tentative pour donner aux Lactobacillus le règne exclusif sur votre moût et pour de nombreux brasseurs les résultats de ces essais ont été ternes ou entachés par des faux goûts. Malgré cela, de nombreux brasseurs ont utilisé avec succès des procédés pour produire des bières réussies avec des niveaux d'acidité lactique propre.

L'objectif de la première partie de cet article est d'examiner les différentes méthodes utilisées pour produire une acidification rapide de la bière et de discuter des meilleures pratiques à suivre lorsque l'on utilise l’une ou l’autre de ces méthodes de production.

Partie 1 – Méthode du Sour Mash - Acidification de la maische

Matériel 


To make a sour mash you’ll need malt, water, a spoon, a thermometer, a pot and a vessel to hold the sour mash (a sour mash tun). An insulated cooler will work as a sour mash tun. It should be just big enough to hold the sour mash and have as little extra headspace as possible. L. delbruckii naturally resides in malt, so you don’t need a culture of the bacteria (although cultures are available from Wyeast).

Timing


Making a sour mash is simple. You’ll need to start two to four days before brewing day. A small sour mash should be between 5 to 15 percent the size of the main mash. (For example, if your recipe calls for 10 pounds of grain, you should make your sour mash with 0.5–1.5 pounds of malt.) For a sour beer, your sour mash should be at least 20 percent the size of the main mash or larger.
Recette



Le Sour Mash


Le Sour Mash est un processus dans lequel un empâtage classique est réalisé, mais le moût est ensuite laissé au chaud pendant plusieurs heures après l'inoculation avec des Lactobacillus. Cet ensemencement peut provenir soit d'une culture de souche pure de Lactobacillus, d’un starter de Lactobacillus ou par l'ajout d'une petite proportion de grain de malt de base non broyé, qui posséderont naturellement une ou plusieurs souches sauvages de Lactobacillus sur leurs enveloppes. Après qu’un certain niveau d'acidification soit atteint, la maïsche est filtrée normalement et suivie par les pratiques classique d'ébullition et de fermentation.

L'avantage de cette méthode est le fait que les Lactobacillus et les autres bactéries présentes dans le moût seront détruites par l'ébullition et seule une bière ainsi stérilisée ira dans les équipements de fermentation. L'inconvénient de ce procédé est que, sur les trois méthodes présentée, c’est la plus difficile à contrôler et le plus susceptible de donner des faux goût.

Les pratiques suivantes vous aideront cependant à obtenir les meilleurs résultats possibles à partir d'un Sour Mash, mais comme nous le verrons dans la partie 3, elles ne sont pas assurées d’un succès.

Sour Mashing en pratique:

Pratiquer un empâtage classique en multi ou mono palier comme édicté par votre équipement ou selon la recette suivie.

Après la fin de votre palier de saccharification, réduire le ph de la maïsche à 4.5 en ajoutant de l’acide lactique alimentaire ou de l’acide phosphorique. Vous pouvez aussi éventuellement ajouter du Malt Acide (ajouté après le palier de saccharification). Le Malt Acide fait chuter le pH d’une moyenne de 0.06 à 0.1 % par % du total du grain. Cela équivaut à rajouter 7 à 10 % du total de la mouture pour un pH habituel de 5.2

Vérifiez votre pH à l'aide d'un pH mètre ou de bandelettes de test et ajuster au besoin avant de continuer.


Assurez-vous d'avoir bien fait un palier de Mash-out qui atteint la température de 75°C pendant au moins 10 minutes pour assurer l'inactivation des enzymes et un blocage du ratio entre les sucres fermentescibles et non fermentescibles.

Refroidir le moût en dessous de 48°c, puis ajouter les Lactobacillus d’une souche pure ou en ajoutant une petite portion de grain de Malt non broyé. Dans chacun de ces procédés, l’utilisation de souche pure sera susceptible de donner des résultats plus prévisibles et de réduire les risques de contamination par des bactéries productrices de saveurs non désirées.

Éliminer l'oxygène de la cuve d’empâtage en “flashant” le récipient avec une couche de dioxyde de carbone ou d'azote. La cuve d’empâtage doit être scellée le mieux possible pour éviter l'oxygène tout au long du Sour Mash. Ces gaz inertes peuvent être insufflés directement dans le moût ou ajoutés par le haut au dessus de la couche de liquide car ils sont plus lourds que l'oxygène et le chasserons. Si votre équipement le permet, un mince filet de gaz inerte peut être utilisé pour assurer continuellement un environnement anaérobie au cours de processus de Sour Mash.

La température du Sour Mash doit être maintenue le plus possible entre 44°C et 48°C pendant tout le processus d’acidification du moût.

Vérifier la progression de votre fermentation au Lactobacillus à l’aide d'un pH-mètre toutes les 6 à 12 heures. Un pH d'environ 3,6 est généralement équivalant à une acidité appropriée pour les styles comme les Berliner Weisse ou les Gose. Un pH d'environ 3,3 sera fortement acide, équivalent à de nombreuses bières de style lambic jeunes. Gardez à l'esprit que pour pH inférieur à 3,4 ou 3,5, certaines souches de Saccharomyces auront des difficultés à produire une fermentation propre. Dans ce cas, il peut être préférable d'utiliser une fermentation mixte ou 100% Brettanomyces, car cette famille de levure peut rester en bonne santé à des niveaux de pH bas et en dessous de 3.0.

Après que votre moût ait atteint le pH désiré, augmenter le trempe à 77°C à 82°C et rincez comme à l'accoutumer.

Un pH initial de 4,5 éliminera généralement tout risque d’infection bactérienne pouvant provoquer une intoxication alimentaire mais faite preuve de prudence élémentaire en goûtant le résultat d'un Sour Mash. Seul un pH faible et la présence d'alcool à partir de la fermentation des levures peuvent assurer que votre produit fermenté est sans danger.

Méthode du Sour Kettling (Acidification dans la cuve d'ébullition)

Très similaire au processus de Sour Mash, le Sour Kettling permet de générer un moût acide qui peut ensuite être porter à ébullition afin de le stériliser avant de le transférer vers votre équipement de fermentation. Par dessous tout, l'acidification dans la cuve d'ébullition permet une plus grande polyvalence et comme processus, il peut être plus facilement contrôlé. Cette méthode vous permet donc de choisir de tuer les Lactobacillus avant la fermentation par les levures ou de permettre de poursuivre leur activité lors du mûrissement de la bière.


Le Sour Kettling commence par l'utilisation d'un brassage traditionnel et une procédure de filtration et de rinçage complète. Si vous voulez tuer les Lactobacillus avant la fermentation, alors il faut effectuer les étapes du Sour Kettling avant l'ébullition. À l'opposé, si vous voulez laisser des Lactobacillus dans votre produit final, l'ébullition sera effectuée avant la procédure de Sour Kettling.
Very similar to the sour mashing process, sour kettling allows you to produce a sour wort that can then be boiled for sanitation before moving it into your fermentation equipment.  Overall though, souring in the boil kettle allows for greater versatility and as a process can often be more easily regulated.  This method also allows you to choose whether to kill the Lactobacillus before fermentation by yeast or to allow its continued activity in your aging beer.  Sour kettling begins with the use of a completely standard mashing and sparging procedure.   If you want to kill Lactobacillus before the rest of your fermentation, then you will perform the steps of sour kettling before the boil.  Oppositely, if you want Lactobacillus to survive into your final product, then the boil is conducted before the sour kettling procedure.


Sour Kettling en pratique


 Si vous choisissez de faire bouillir avant la fermentation afin d’éliminer les Lactobacillus lors de la fermentation, la première étape consistera à ajuster le pH de votre moût à 4,5 en utilisant soit de l’acide lactique de qualité alimentaire ou de l'acide phosphorique.


Si vous choisissez de faire bouillir avant acidification afin de conserver des bactéries lactiques dans la phase férmentaire, assurez-vous que votre recette ne comprend pas d’ajouts de houblon ou que ces ajouts ne produiront pas plus de 10 IBU dans la bière finale. Trop d’acide alpha ou d’huiles essentielles en général, vont inhiber les Lactobacillus et empêcher l'acidification par l'intermédiaire de leur fermentation. Après l'ébullition, ajuster le pH à 4,5 comme mentionné précédemment.


Refroidir le moût au-dessous de 48°C avant introduction de votre culture de Lactobacillus ou l'ajout d'une poignée de malt de base dans votre cuve d'ébullition. Comme pour le Sour Mash, les cultures pures sont plus prévisibles et moins susceptibles de produire une contamination par des bactéries produisant des faux goût.
Insuffler le maximum de CO2 ou d'azote dans la cuve et la sceller le mieux possible.


Envisager de purger l’oxygène contenu dans le moût en faisant barboter un gaz inerte à travers la moûture pendant quelques minutes. Comme précédemment, si votre équipement le permet, ces gaz peuvent laisser à barboter lentement dans la cuve fermée pendant toute le Sour Kettling pour maintenir un environnement anaérobie.

Maintenir le moût à une température comprise entre 44 et 48 °C autant que possible.


Tout comme le Sour Mashing, vérifier le pH de votre moût toutes les 6 heures.


- Lorsque le pH souhaité a été atteint, procéder soit à une ébullition normale, ou si vous avez déjà procédé à l'ébullition et souhaité préserver des Lactobacillus dans votre bière, effectuer le transfert vers les cuves de fermentation en utilisant les pratiques sanitaires appropriées.


Sour Worting dans le fermenteur


This third process assumes that you wish for Lactobacillus to survive and remain active in your fermenting and finished beer.  On both a homebrew and commercial scale, it is best to use either pure laboratory-sourced cultures or cultures collected and maintained from starters which have proven to be free of off-flavors and aromas.  Doing so, in combination with the other best practices discussed, will virtually ensure that your beer remains free of unwanted microorganisms and their off-flavors.  For commercial brewers who cannot heat their fermenters , this process is identical to sour-kettling after a standard boil.  When developing recipes for sour-wort beers, the alpha-acid level from hop additions must be restrained to less than 10 IBUs to prevent the inhibition of Lactobacillus.


En pratique Souring in a Fermentation Vessel


Mash and Boil your wort as normal. During the boil, adjust the pH to 4.5 using food grade lactic or phosphoric acid.
Cool the wort to below 120° F and transfer into a sanitized fermentation vessel. Ensure proper closed & sanitary transfer practices.  I have run 110° F wort into glass carboys without incident, but I do not recommend that this be done routinely.  It is far better to use a stainless vessel (for homebrewers, either 5 gallon Cornelius or half-barrel Sankey kegs work well) for these hot wort transfer and fermentation procedures.


Purge both the wort and the fermentation vessel with carbon dioxide using either the line out on a corny keg or by using a sintered stone in other fermentation vessels.
Pitch a pure culture of Lactobacillus or a Lactobacillus starter that is free of off-aromas.


Maintain a fermentation temperature between 112° to 120° F.  This can be achieved on the homebrew scale by the use of a ferm-wrap or other fermentation heating element and an insulated chamber such as a small chest freezer or a large insulated picnic cooler.


As in previous methods, check the pH every 6 hours.


When the desired pH is reached, cool the wort to the proper yeast pitching and fermentation temperature (between 45° to 55° F for lager Saccharomyces or between 65° to 75° F for ale Saccharomyces orBrettanomyces)


Oxygenation at this point is very beneficial for the yeast and will not harm further Lactobacillus flavor development


Pitch one or more Saccharomyces or Brettanomyces strains and proceed through a standard alcoholic fermentation from this point forward.
The ultimate goal of these three processes is the same:  Produce a beer with a pleasant level of lactic acidity that is free of off-flavors in a short period of time.  Lets now look at how to smell and taste the beer to detect the most common off-flavors that can arise from these fast souring methods.



Step Five: On Brewing Day

Stir the sour mash into the main mash. The pH of the sour mash should be around 4. Add half of the sour mash, then check pH.  Keep adding until pH is 5.2. (Follow pH meter instructions with care. You might have to cool down the mash to get specific readings).

If you are making a sour beer, add only a small amount of the sour mash — 5 to 15 percent of the main mash — to the main mash. Keep the remainder of the sour mash separate until after starch conversion is complete. Adding the whole large sour mash to the main mash will lower the pH below 5.2. and result in lower yields. Once the main mash is finished, add the rest of the sour mash. After mashing, proceed with recirculation, run-off and sparging as you normally would. 

If you are experimenting for the first time, make a larger sour mash than you need and hold it for just two days. It’s easier to maintain a larger sour mash for two days than managing a smaller sour mash for four days. There is less work involved and less opportunity for contaminants to grow. A sour mash that is infected with unwanted organisms could taint your beer with off flavors. The smell and appearance of the sour mash should indicate the presence of any growth. When in doubt, throw it out!

Chris Colby is a contributing writer for Brew Your Own. He lives in Bastrop, Texas.

Lactobacillus 2.0
or: How I Learned to Stop Worrying and Love the Sours  Advanced Techniques for Fast Souring Beer


In Fast Souring with Lactobacillus, I discussed three major ways to quickly sour wort before a primary fermentation with yeast.  In this article, I am going to narrow this down to a single sour brewing pipeline with a few  variable options depending upon your goals for the final beer.  This simplified souring pipeline is designed to give brewers a repeatable process by which to create quickly soured beers while both avoiding major problem areas encountered with previously discussed methods as well as optimizing the fermentation profile and flavors produced by various known strains of Lactobacillus.  This process is visualized in the following flow chart:


At this point you may be noticing that, in all paths, the beer is boiled before adding Lactobacillus.  Many brewers may be asking:  Why do I need to do this? Don’t mash temperatures pasteurize the wort?
It turns out that in many cases, mash temperatures are not enough to fully sanitize wort.  The strongest trend I have seen in all of the troubleshooting emails I receive is this:  Beers that don’t receive at least a short boil before souring undergo far more problematic fermentations.  In most cases, the preventative measures discussed in the previous article (temperatures above 115° F, pre-acidification to pH 4.5, and avoidance of oxygen) will prevent unwanted bacterial fermentations.  




Empâtage et rinçage habituel en fonction de votre équipement. Les bières acidifiées par un Sour Mash rapide n’ont pas besoin d’un taux plus important de sucres non fermentescibles.
Voulez vous des Lactobacilles lors de la fermentation qui se retrouveront aussi dans le produit fini ?


However, these steps do not prevent unwanted fermentation by wild yeasts and this turns out to be a frequent problem.  When beer is neither boiled before souring nor are these protective steps in place, any host of problems, infections, and off-flavors can arise.
This is a major change from advice given previously both here and by many other sources.  The previous advice was based upon a standard concept called “Vat Pasteurization” which is typically applied in the milk processing industry.  Research into milk pasteurization has found that large volumes of milk held at or above 145° F for at least 30 minutes will be sanitized.  While typical mashes meet these time and temperature requirements, experimental testing and the experience of numerous brewers indicates that mashing alone is simply not enough to sanitize wort.  Theories which may explain why this is the case include:
Wort chemistry and the physical dynamics of the grain / water mixture may provide some form of protection to microorganisms against inactivation by standard mash temperatures.
Small pockets of the mash and / or potential “dough balls” within the mash may never actually reach the temperatures needed for pasteurization to occur
A second major change is the recommendation to target temperatures during the Lactobacillus fermentation that may be lower than 115° F.  In our previous article this temperature was recommended to discourage contamination by bacteria of the Clostridium genus.  While I still advise using this temperature for “wild”Lactobacilli originating from inoculation by grain or other unknown origins, there are several lab cultured strains available that will not acidify the wort properly at 115° F.  I have compiled a chart to help brewer’s target a temperature which will yield a fast souring of their wort based on the preferred fermentation environment of theLactobacillus strains listed.  Keep in mind that, when using some of these strains, we will lose the protective factor of high temperature and therefore both sanitation and the other precautionary methods available will become even more important to avoiding the off-flavors of contamination.

It is important to remember that when Lactobacilli are creating lactic acid, they are doing so as a part of their normal metabolic growth and survival functions much in the same way that yeast do so when producing alcohol and CO2.  While it is rarely discussed, this means that pitching rate is something that we need to consider.  This is especially true when trying to troubleshoot a Lactobacillus fermentation that did not get sour enough or took longer than desired to get sour.
 
Lactobacillus Pitching Rates
There are two methods that can be used to ensure that we have an adequate pitch of Lactobacillus.  The first of these methods bases the pitch rate on estimated cell counts per mL of wort.  The second method is based on the volume of starter wort created and assumes that the Lactobacillus culture will reach a maximum cell density within that wort somewhere between 15 and 30 hours after pitching.  I am comfortable recommending either technique because, when you crunch the numbers, both methods come out to yield approximately the same results.
Pitching Based on Cell Count:
When calculating the amount of Lactobacillus to pitch, about 10 million Lactobacillus cells per mL of wort are required to sour a beer within 24 to 48 hours depending on the species or strains being used.  This general rule was derived experimentally at the Gigayeast laboratory after testing a number of Lactobacillus strains under a variety of conditions.  This estimate also very closely matches my own experimental observations of beers that have successfully soured quickly in my brewery.  My observations have suggested that the pitch rate forLactobacillus should match the traditional pitch rate quoted for ale strains of Saccharomyces: 1 million cells per mL of wort per degree Plato.
Pitching Based on Volume:
The second method for pitching Lactobacillus is recommended by Lance Shaner of Omega Yeast Labs.  This method is based upon using Omega Yeast’s Lactobacillus Blend and involves the creation of a one liter starter for 24 hours before pitching.  Lance has found that this one liter starter will typically be effective in creating robust acidification of up to 2 barrels (62 US gallons) of wort within 24 hours.
A number of studies have found that when Lactobacilli are cultured in the lab using MRS media or other similarly buffered nutrient solutions, they can reach a maximum cell density of nearly 9 billion cells per mL of solution.  However, the studies I reviewed also indicated that under non-ideal conditions (like in the starters we are capable of producing), the cell density of a solution would more realistically reach between 2 to 5 billion cells per mL.  If you assume that the average Lactobacillus starter will reach a peak cell density of about 2 billion cells per mL within 24 hours, that yields a theoretical pitch rate of 8.5 million cells per mL when pitched into 2 barrels of wort.  This estimate provides some theoretical validity to the idea that either method can be an effective way to ensure that enough Lactobacilli are pitched into a wort to ensure fast souring.
Now that we know how to determine approximately how much Lactobacillus we will need to pitch for fast souring, let’s take a look at how to create starters to grow these amounts:
 
Lactobacillus Starters
Earlier this year, Samuel Aeschlimann of Eureka Brewing ran a series of experiments which compared a number of traditional and modified starter solutions in order to determine whether any of them could yield Lactobacillus growth rates similar to those that occur in MRS media. My recommendations here are based upon Sam’s formula with a minor tweak in sugar composition based upon my own research.  The goal of this starter recipe is to provide:
The nitrogen and inorganic nutrients required for optimal growth
A sugar composition of 2 to 3% w/v glucose, which has been shown to be optimal in stimulating Lactobacillusgrowth and metabolism.
Enough buffering capacity to prevent the Lactobacillus from slowing their own growth via an over-acidification of their environment.
To create a starter optimized to grow Lactobacillus, combine the following ingredients per Liter of wort and boil for 15 minutes:
90 grams Dry Malt Extract
20 grams Dextrose (Glucose) (sold to brewers as corn sugar)
20 grams Calcium Carbonate (CaCO3 / chalk)
1 gram Yeast Nutrient or DAP (diammonium phosphate)
Cool this starter solution down to the temperature preferred by the strain of Lactobacillus that you are culturing and maintain this temperature as best as possible for 24 to 36 hours.  You want to seal the flask with a rubber stopper and airlock to prevent additional oxygen from entering the starter solution.  I would recommend using a stir plate set on a low rotation.  This low setting will help to encourage growth by increasing microbial access to nutrients as well as aiding in the removal of CO2 for heterofermentative strains.  It is best to time your starter’s creation so that it can be pitched into the wort you intend to sour between 24 to 48 hours after making the starter.  However, if this is not possible, follow the same guidelines that you would for yeast starters: Store the unused starter under refrigeration and use within one week’s time to maintain high viability.
Lactobacilli do not quickly flocculate after fermentation in the same way that many strains of brewer’s yeast can.  This means that to ensure fast souring you will need to pitch the entire starter volume into the wort.  One caveat here is to decant the starter wort off of any chalk sediment at the bottom of the flask.  Not all of the calcium carbonate will always enter solution in the starter and we do not want to pour this into the beer if we can avoid it.
When creating starters, any fresh single pitch of a commercial strain will provide ample initial Lactobacilli cells to produce an effective starter within 24 to 36 hours, this includes single White Labs vials which contain approximately 1.8 to 2.7 billion cells per tube.  One practical way to ensure that your starter culture is multiplying as expected is to monitor for turbidity changes.  Much like yeast starters, Lactobacillus starters will become increasingly cloudy as the cell density rises.
Recently, many home and craft brewers have begun experimenting with the wide variety of Lactobacillus strains or blends sold in health food stores as digestive probiotics.  These cultures are not only cheap and easy to find, but also provide a wider variety of potential flavor subtleties when used in the fast souring process.  If using liquid probiotics, you can use the cell estimates on the packaging to determine whether a starter will be needed.  When in doubt, go with the starter.  If using freeze-dried (lyophilized) probiotics (capsule forms), it is best to open up the capsules and rehydrate the powderedLactobacilli inside using distilled water in the same way that dry-yeast packages should be rehydrated.  After rehydration, I would recommend adding this slurry to a starter to ensure a healthy and adequately sized pitch.

A microscopic view of both Saccharomyces (large round cells) and Lactobacillus(small rod shaped cells) in one of the author’s fast souring beers. After acidification to pH 3.45, this beer was fermented with WLP001, blended with fresh mangos, and dry hopped using galaxy hops.
While both cell count estimates and starter volume estimates can be used to successfully ensure that enough Lactobacilli are pitched for fast souring, most brewers will find pitching based on volume to be more practical.  Lactobacillus cells are much smaller than yeast cells and therefore they are more difficult to accurately count under a microscope.  Additionally, different species and strains of Lactobacillus will grow to differing cell densities and at differing rates.  Therefore, it is best to err on the side of caution.  We want to ensure that we pitch enough cells to ensure fast souring, but over-pitching of Lactobacillus tends not to cause any significant problems for the brewer.  Luckily, this is because, in our unbuffered worts, the growth and souring potential of Lactobacillus is a self-limiting process that will generally bottom out somewhere at or above a pH range of 3.0 to 3.4.  If the lower portion of this range is more acidic than you would like to target, simply make sure to closely monitor your pH and end the souring process as discussed above when you reach the desired pH level.
I have created the following table based upon the minimum pitch rates for the volumes of beer listed, but, if in doubt, pitch more.

 
Recipe Design and Process Considerations
It is important to remember that a beer’s recipe, wort production, and fermentation conditions are all important considerations in the fast souring process.  Starting with the mash, a beer’s ability to be soured quickly can be enhanced by producing a more fermentable wort through the targeting of lower mash saccharification temperatures.  This is because most strains of Lactobacillus will preferentially consume the simplest sugars available, and these sugars tend to be formed in higher proportions at lower mash temperatures.
The IBU level of a beer is such an important consideration when fast souring that I chose to mention it directly in the flowchart above.  Nearly all commercial strains of Lactobacillus are extremely sensitive to hops.  Even the more “hop tolerant” strains such at L. brevis tend to lose their ability to significantly acidify beers with an IBU level of 5 or greater.  Luckily, as seen above, brewers can easily add hops to a beer by boiling after it has been soured.  Alternatively, dry-hopping is an excellent option for adding hop character to a mature sour beer.
Original gravity (and associated final ABV) is another important factor to consider when designing a beer to be fast soured.  Any beer with an original gravity higher than 1.040 SG (10 Plato) will be soured more slowly or incompletely by Lactobacillus.  When designing higher ABV sour beers, plan to allow the Lactobacillus to survive into the fermentation / aging vessel so that it can continue to slowly acidify the beer over a period of several months.
 
Quality Control
While I wrote extensively about this topic in the article Fast Souring With Lactobacillus, it is such an important concept that it bears repeating.  Lactobacillus-only fermentations should not smell like vomit, bile, parmesan cheese, stinky feet, or feces.  The presence of any of these aromas before the addition of Saccharomyces orBrettanomyces is an indication of infection by an unwanted species of bacteria such as Clostridium butyricum.  Additionally, medicinal, plastic, smoky, or phenolic aromas or flavors are undesired and are an indication of infection by a strain of wild yeast.
It is normal for Lactobacillus acidified wort to smell sweet, bready, doughy, musty, buttery, vegetal, or reminiscent of sauerkraut.  These aromas are due to byproducts of heterofermentative fermentation byLactobacillus such as diacetyl and acetaldehyde.  Some of the characteristic doughy and musty aromas may persist into the final beer, but any potential sweet, vegetal, buttery, and sauerkraut aromas will generally be gone after fermentation by Saccharomyces or Brettanomyces.
Many of the commercially available strains of Lactobacillus can undergo heterofermentative fermentation, meaning that in addition to producing lactic acid, they can also produce alcohol and carbon dioxide.  This fact has led many brewers to assume that these strains will sometimes nearly or fully ferment their wort before the addition of brewer’s yeast.  While heterofermentative strains can slightly begin to attenuate a beer, a drop of greater than 8 points of specific gravity (2 points Plato) within 24 to 48 hours is almost always a sign of yeast contamination.  Such contamination may not negatively impact the beer in regard to off-flavor production, but it may reduce the souring potential of the Lactobacillus through competition for simple sugars.
 
Ending Thoughts
It is an exciting time for sour beer fans both in the United States and abroad.  Worldwide, a greater number of craft brewers and homebrewers are beginning to experiment with sour beer styles than ever before.  The ability to create flavorful sour beers both quickly and cost-effectively is a valuable tool for the versatile brewer.  It is my hope that this article, when read in tandem with Fast Souring with Lactobacillus, will provide both home and craft brewers with a well-rounded understanding of how to produce delicious sour beers quickly while maintaining a high degree of quality.
Cheers and Happy Brewing!
Matt “Dr. Lambic” Miller


Part 2 – Detecting Common Off-Flavors and Aromas and Understanding Their Cause.
As a brewer myself, it is always my goal to produce the best beer possible and it is from this perspective that I will launch into a discussion about off-flavors and aromas. That being said, I also know that, for many brewers who are first starting to experiment with sour beer, it can sometimes be difficult to distinguish between “bad funk” and “good funk” in these beers.
In general, Lactobacillus in isolation (the goal of these methods) should produce a far simpler flavor profile than produced by either traditional brewers yeast or the common sour beer yeast Brettanomyces.  The primary product of Lactobacillus is lactic acid, which is a simple organic acid with a soft pleasant sourness.  Common foods that feature this acid include Greek yogurt, kefir, sauerkraut, and sourdough bread.  For the candy fans, the addition of lactic acid is what differentiatesSour Patch Kids Extreme” from the classicSour Patch Kids”.
The fermentation of Lactobacillus will also give its beers a fairly subtle yet classic mustiness.  This can smell a bit like a damp basement or the forest after a rainstorm.  Another aroma commonly associated withLactobacillus is a floury smell associated with sourdough bread and sourdough starters.  These are light aromas easily overpowered by other additions to the beer such as hops or fruit.  Additionally, the aroma and flavor compounds produced by brewer’s yeast strains or Brettanomyceswill easily mask these characteristics.  Despite this, I believe it is the presence of these non-acidic  characteristics that differentiate beers actually fermented with Lactobacillus from those that have simply received a large addition of food-grade lactic acid.  In my opinion, this latter process creates an inferior product which tastes somehow artificial.
Lactobacillus beers, when smelled at room temperatures, should not “stink”.  This is especially true after a primary fermentation by Saccharomyces or Brettanomyces.  Immediately after the Lactobacillus fermentation, it is common for the wort to smell:
Musty or Floury (This would be considered “good funk”)
Sugary, Syrupy, & Sweet (Because Lactobacillus produces only a minute level of attenuation in comparison to yeast)
A little Buttery (Occasionally, because certain strains of Lactobacillus can produce diacetyl in their fermentation)
Lactobacillus species are divided into two groups, homofermentative and heterofermentative.  Homofermentative species will only produce lactic acid during their fermentations.  Alternatively, heterofermentative species will primarily produce lactic acid but can also produce ethanol, carbon dioxide, and acetic acid during their fermentations.  I bring this up because, in very low levels, this acetic acid will add flavor complexity and should not be considered an off-flavor when using these species / strains.  On the other hand, if there is a strong and distinct aroma or flavor of vinegar, this would generally be considered undesirable and is likely due to contamination of the wort by Acetobacter or other unwanted aerobic microbes.
If using a clean ale strain such as White Labs WLP001, Wyeast 1056, or Safale US-05 to ferment your wort after souring with Lactobacillus, you would expect the fully attenuated beer to have only a slightly musty and fruity aroma, as well as a clean and simple sour flavor.
Lets now take a look at the aromas and flavors that we do not want to detect in either the wort or finished beer:
Parmesan Cheese, Rancid Milk, or Stinky Feet (Isovaleric Acid)
Vomit or Bile (Butyric Acid)
Fecal, Manure, Poopy Diaper (Aromatic Indoles)
A strong presence of Vinegar (Acetic Acid)
Bandaid, Liquid Smoke, Medicinal (Phenolic Compounds)

These batches of sour red ale undergo a sour worting process before being pitched with Saccharomycesand Brettanomyces.
When I am brewing a batch of sour beer using a Lactobacillus-first fermentation, the presence of any of these characteristics in my beer would lead to the batch being dumped.  This is because I am not willing to spend time aging a beer with off-flavors in the hope that they will eventually become better.  While personally I’m not willing to age such batches, three of the chemical compounds that are listed above can be either reduced or turned into flavor positive compounds by the yeastBrettanomyces.  These compounds include isovaleric acid, butyric acid, and certain phenolic compounds.  If you detect these compounds in very low levels, aging withBrettanomyces can eliminate them over time.  However, if any of these compounds are intensely strong, it is best to dump the batch and review your processes.  A good rule of thumb would be that if a flavor or aroma is off-putting enough that you would not drink several pints of the beer, then save your efforts and dump it.
When tasting your beer for off-flavors, it is sometimes very useful to drink another commercial example of the style that is known to be free of defects.  This side-by-side comparison can really help to highlight flavors in your beer that you may not have otherwise noticed.  Additionally, because strong lactic acid can be overwhelming to some taster’s palates, it can be useful to adjust your palate to intense acidity before analyzing the flavors in your beer.  This can be done with a favorite bottle of strongly sour beer, a glass of water blended with lemon-juice concentrate, or by eating a few sour candies like Sour Patch Kids or Warheads.
A few more general tips for tasting and smelling your beers include:
Pour the beer into a tulip glass or other similar aroma-promoting glass.
Smell and taste the beer when it is at cellar temperature and at room temperature. Tasting or smelling the beer at cold temperatures will mask or reduce many flavor and aroma compounds.
When smelling the beer, don’t be afraid to get your nose deep in the glass and take several good whiffs in a row. If your nose needs a reset, smell the skin of your clean dry arm for several seconds.
When tasting the beer, pull some air into your mouth with the sip. This helps to aerate the sample and bring out both flavor and aroma compounds.
Avoid tasting the beer after smoking, chewing tobacco, or eating any strongly spiced or otherwise potently flavored foods.
If you are hunting for subtleties, don’t be afraid to ask for help. Genetically we all have a very wide range of sensitivities to different chemical compounds.  A group of good analytic tasters can be the most useful tool in a brewer’s arsenal.
At this point we have covered both the best-practices to be used while fast-souring with Lactobacillus and how to analyze our beers for both positive and negative results.  For the practical brewer, you now have all the tools you need to go forth and brew delicious fast-soured beers.  However, for the inquisitive brewers, I will now wrap up this article with a discussion of the science behind these practices.
Part 3 – Fast Souring Science
Before jumping into a discussion of the organisms responsible for producing off-flavors in these fermentations, I need to mention a caveat to this information:  Sour mashing, sour kettling, and Lactobacillus-only fermentations are relatively recent products of the American craft brewing community.  There have been no detailed scientific studies directly looking at the organisms that are in play when these processes fail.  However we can make fairly educated guesses as to the identity of the organisms involved based upon the chemicals and off-flavors that they leave behind.  Many of these organisms have been studied in other food products or in other processes related to industrial brewing (practically all well-funded beer science has been performed in the arena of industrial lager brewing).  Deducing the identity of the organisms that commonly compete with Lactobacillus in these fermentations allows us to re-engineer the process to reduce or eliminate the risk of these unwanted microbes.
Butyric Acid Bacteria

Butyric Acid
The easiest of these organisms to identify are members of the Clostridium family.  These bacteria, especially Clostridium butyricum, are well known in the brewing industry as producers of butyric acid due to their propensity to infect sugar syrups in bulk storage containers.  Clostridium are obligate anaerobic (they cannot survive in the presence of oxygen), endospore forming, gram positive, rod shaped bacteria which metabolize simple sugars to produce butyric acid.  Butyric acid both smells and tastes like vomit, bile, and rancid milk or cheeses.  This chemical is present in low doses in goat and sheep milk, butter, and parmesan cheese.  It is also present in human vomit.
Clostridium, and other less common butyric acid bacteria, while requiring the same oxygen free environment thatLactobacillus prefers, cannot tolerate the same pH and temperature ranges as Lactobacillus.  WhileLactobacillus can comfortably thrive between 115° and 120° F, Clostridium dies at temperature above 112° F.  Additionally, while Lactobacillus purposely acidifies its environment in order to outcompete acid-intolerant bacteria, Clostridium prefers an optimum pH of 6.3.  As the pH of its environment drops near 5.0, Clostridiumloses its ability to produce butyric acid, and at a pH of 4.7 or below, these bacteria become completely inactivated.  These tolerances produce our recommendations to always pre-acidify the wort to a pH of 4.5 and maintain a temperature above 112° F when possible.
Indole Producing Bacteria

Indole
The presence of fecal aromas or flavors in a sour beer are an indication of an infection by bacteria known as coliform bacteria.  These bacteria include families such as Citrobacter,Klebsiella, Enterobacter, and Escherichia and are found throughout nature.  One species, E. coli, is a common bacteria found in the large intestines of most humans.  This species also garnishes media attention from time to time due to its occasional ability to become pathogenic and cause a toxic diarrhea.  Many species of these bacteria metabolize various amino acids to produce the chemical indole, a chemical which smells strongly of feces.  These bacteria are rod shaped facultative anaerobes (preferring oxygen free environments but able to survive in its presence), which do not form spores.  Certain groups of these bacteria can survive at temperatures above those preferred by Lactobacillus.  Luckily for use, these bacteria, while able to survive a low pH environment, do not reproduce or metabolize well as the pH approaches 4.4. Therefore, our recommendation of lowering the pH to 4.5 before fermentation will help to prevent these bacteria from producing off-flavors in our fermentations.
Bacterial Production of Isovaleric Acid

Isovaleric Acid
Unfortunately, this narrative becomes more complicated when we look at bacterial sources for isovaleric acid.  One definitive source of this off-flavor is metabolism of the amino acid leucine by a bacterium called Bacillus subtilis. This bacterium is present on human skin and is responsible, in part, for the production of foot odor.  This rod shaped bacteria is known for its ability to form a protective endosperm which allows it to survive a wide range of environmental conditions.  Luckily, this bacteria is an obligate aerobe (requiring oxygen to survive) and therefore can be prevented from affecting our sour fermentations when we maintain an oxygen free environment.
A second, and less controllable source of this off-flavor may be an interaction between a bacteria commonly found in yogurt cultures, Streptococcus thermophilus, and the very Lactobacillus which we are utilizing in our souring fermentations.  Lactobacillus, in isolation, does not possess the metabolic enzymes needed to convert leucine into isovaleric acid.  However, it seems that when S. thermophilus is present, it can potentially supplyLactobacillus with the chemical intermediates needed to perform this metabolism.  The bad news regarding this interaction is the fact that S. thermophilus thrives in all of the same environmental conditions as Lactobacillus.  Therefore the only process control that can prevent its influence in our sour fermentations is the use of good sanitation practices.

When working with wild harvested Lactobacillus, its always a good idea to test your results first using small starter batches.
This potential interaction is one of the reasons why I strongly prefer to use only pure cultures of Lactobacillusor starters which have already proven to be free of off-flavors.  The temperatures of mashing will generally sanitize our wort and the process of boiling definitely will. (2015 Update: Always perform at least a 15 minute boil before beginning a fast souring process)  As long as from these points forward only known cultures are introduced, there will be little to no risk of contamination.  In fact, while I have used Lactobacillus first fermentations dozens of times, I have never experienced any of these common off-flavors in my beers.
Another reason to consider only using known cultures is the fact that bacteria can and do frequently swap genetic material, allowing certain strains to develop properties that they previously lacked.  Therefore, the only way we can ever really know what is fermenting in our beers is to ensure that we put only the bacteria that we want into them.  With that said, following the best practices outlined here will almost certainly yield positive results in your breweries.
Hopefully, this review has been interesting, informative, and helpful to brewers looking to develop a quick and simple acidity in their beers.  These processes alone work very well when producing styles like Berliner Weisse and Gose, and can be very useful for establishing a baseline acidity in other more complex styles as well.  As always, please email me at matt@sourbeerblog.com with any questions.
Have fun and brew sour!
Cheers!
Matt “Dr. Lambic” Miller
November 2015 Update: For those looking to expand their fast souring knowledge with techniques such asLactobacillus pitch rate, starters, and recipe design, check out our new follow up article: Lactobacillus 2.0 – Advanced Techniques for Fast Souring Beer!


The most common contaminant of a sour mash is Clostridium butyricum. This anaerobic bacteria produces butyric acid, a foul-smelling compound that turns the mash rancid. Sour mashes infected with Clostridium should be thrown out. Luckily, these bugs are inactive above 112° F. Keeping the sour mash above this temperature will inhibit Clostridium.

Acetobacter, an acetic acid-producing bacteria, can also infect sour mashes. These aerobic bacteria grow on the surface of the mash if oxygen is present and can convert alcohol to acetic acid at pH values as low as 4.5. Keeping the sour mash tun tightly closed to seal out oxygen will inhibit the growth of Acetobacter. It can also be inhibited by raising the temperature above 122° F. (Temperatures above 120° F will stun L. delbruckii, but they will survive unless temperature exceeds a high of 131° F.)

Some heterofermentative Lactobacillus species grow in the same conditions as L. delbruckii. The presence of these bacteria may be detected by the buttery smell of diacetyl. Heating the sour mash above 140° F should kill them, but then you will need to re-inoculate the mash with more L. delbruckii.

References:
Ghoddusi, Hamid B., Richard E. Sherburn, and Olusimbo O. Aboaba. “Growth Limiting PH, Water Activity, and Temperature for Neurotoxigenic Strains of Clostridium Butyricum.” ISRN Microbiology2013 (2013): 1-6. Web.
Goodwin, Jay, and Scott Moskowitz. “The Sour Hour / Episode 4.” The Sour Hour. The Brewing Network. Concord, CA, 20 Nov. 2014. Radio. (Features guest brewer Khris Johnson of Green Bench Brewing in St. Petersburg, Florida. Khris is the first brewer that I’ve heard make the direct connection between certain sour mash/sour kettle off-flavors and isovaleric acid)
Helinck, S., D. Le Bars, D. Moreau, and M. Yvon. “Ability of Thermophilic Lactic Acid Bacteria To Produce Aroma Compounds from Amino Acids.”Applied and Environmental Microbiology 70.7 (2004): 3855-861. Web.
Klocker, Alb. Fermentation Organisms; a Laboratory Handbook. London: Longmans, Green, 1903. Print.
Sakamoto, Kanta, and Wil N. Konings. “Beer Spoilage Bacteria and Hop Resistance.” International Journal of Food Microbiology 89.2-3 (2003): 105-24. Web.
Vriesekoop, Frank, Moritz Krahl, Barry Hucker, and Garry Menz. “125Anniversary Review: Bacteria in Brewing: The Good, the Bad and the Ugly.” Journal of the Institute of Brewing 118.4 (2012): 335-45. Web.
Zhang, Chunhui, Hua Yang, Fangxiao Yang, and Yujiu Ma. “Current Progress on Butyric Acid Production by Fermentation.” Current Microbiology59.6 (2009): 656-63. Web.
Zigová, J., and E. Šturdík. “Advances in Biotechnological Production of Butyric Acid.” Journal of Industrial Microbiology and Biotechnology24.3 (2000): 153-60. Web.

Aeschlimann, Samuel. “Evaluate Starter Media to Propagate Lactobacillus Sp.” Eureka Brewing. N.p., 18 May 2015. Web. 18 Nov. 2015.
Carey, Erin. “Using Calculus to Model the Growth of L. Plantarum Bacteria.” Undergraduate Journal of Mathematical Modeling: One Two UJMM: One Two 1.2 (2013): n. pag. Web.
Gu, SP, Z. Liu, and PZ Song. “The Measurement of Growth Curve and Generation Time of Lactobacillus.” Shanghai Kou Qiang Yi Xue 7.4 (1998): 226-27. Print.
“Lactobacillus.” Milk The Funk Wiki.  Web. 18 Nov. 2015.
LACTOBACILLI MRS BROTH. Lansing, MI: Neogen Corporation, Nov. 2010. PDF.
Siegrist, Jvo. “Lactobacilli.” Sigma-Aldrich. N.p., n.d. Web. 18 Nov. 2015.
Tonsmeire, Michael. American Sour Beers: Innovative Techniques for Mixed Fermentations. Boulder, CO: Brewers Publications, 2014. Print.
Zacharof, MP; Lovitt, RW and Ratanapongleka, K. Optimization of Growth Conditions for Intensive Propagation, Growth Development and Lactic Acid Production of Selected Strains of ‘Lactobacilli’ [online]. In: Engineering Our Future: Are We up to the Challenge?: 27 – 30 September 2009, Burswood Entertainment Complex. Barton, ACT: Engineers Australia, 2009: [1830]-[1838]. ISBN: 9780858259225. [cited 18 Nov 15].
Valík, Ľubomír, Alžbeta Medveďová, Michal Čižniar, and Denisa Liptáková. “Evaluation of Temperature Effect on Growth Rate of Lactobacillus Rhamnosus GG in Milk Using Secondary Models.” Chemical Papers 67.7 (2013): n. pag. Web.
Xiong, Tao, Xuhui Huang, Jinging Huang, Suhua Song, Chao Feng, and Mingyong Xie. “High-density Cultivation of Lactobacillus Plantarum NCU116 in an Ammonium and Glucose Fed-batch System.” African Journal of Biotechnology 10.38 (2001): 7518-525. Print.
 Le deuxième volet de cet article sera une discussion sur la façon de goûter analytiquement vos bières afin de détecter les différentes flaveurs communes ne peut résulter de processus quasi-acidification. Enfin, un troisième élément de cette discussion avec le centre sur la science derrière thèse fermentation, avec un accent sur les différentes bactéries indésirables ne peut rivaliser avec Lactobacillus. Nous allons examiner pourquoi les bactéries de thèse produisent les flaveurs thatthey faire et pourquoi les meilleures pratiques examinées dans le cadre d'une aide pour assurer ne bactéries de synthèse sont tenus à distance.

Références