Choosing the Right Probiotics for Souring Beer

A more-and-more common practice for quick sour beers is to use probiotic pills as a source of lactobacilli for the souring process. Indeed, the Milk the Funk Wiki has a growing list of alternate sources for these bacteria, including many probiotic capsules. A question that seems to rise quite often on this topic is "can I use probiotic brand X for souring beer". So here is a quick guide on figuring out whether a probiotic will work for souring beer.

In general, probiotic organisms fall into four categories when considering using them for souring:

1. Good choices
2. Probably don't matter
3. Avoid under some circumstances
4. Avoid at all cost

---

Good Choices:

Bacteria that represent good choices are those which have the capacity to sour wort, and will do so with a minimal risk of off-flavours. These are solely species belonging to the Lactobacillus genus - i.e. Lactobacillus sp, where sp merely means "any species".  Lactobacillus plantarum and Lactobacillus rhamnosis are two of the more commonly seen probiotic strains, but any probiotic containing bacteria whose name starts with 'Lactobacillus' will work well.

---

Probably Don't Matter:

Species which "probably don't matter" are those which are unlikely to grow in wort; either because the homebrewer lacks the ability to lower the oxygen level in the wort to the point where these organisms grow, or because wort isn't nutritionally compatible with these species. The flip side is that if these organisms grow, they should do the same thing as Lactobacillus - i.e. sour the wort while producing minimal off-flavours. So that's why they probably don't matter - they're not likely to do anything, but if they do end up doing something, they will help your wort sour. Included among these are:

1. Bifidobacteria sp. (again, sp means "any species")
2. Streptococcus thermophilus
3. Leuconostoc sp.

---

Avoid Under Some Circumstances:

Only one group of organisms fall into this grouping - the Saccharomyces, as in species of yeast from the same genus of yeast that brewing yeast come from. At the time of this post the only Saccharomyces commonly seen in probiotics is Saccharomyces boulardii. Saccharomyces sp. fall into the "avoid under some circumstances" category as they will ferment sugars to form alcohol. You probably should avoid these - they will compete with Lactobacillus for sugars, and thus limit acidification. In addition, if you are planning on heating the wort after souring (to either pasteurizing or boiling temperatures), you will boil off the resulting alcohol leading to a beer with very little sugar left for the subsequent fermentation.

So as a rule you will want to avoid these, although it may be an interesting experiment to see what kind of beer you get if you pitch a Saccharomyces boulardii-containing probiotic mix into your fermenter.

---

Avoid At All Cost:

The last group are those you want to keep as far away from your wort, beer and fermenter as possible. These are bacteria which can produce horrid off-flavours and ruin a beer. In this group there are currently three types used in probiotics, but this list may get longer in the future:

1. Clostridium sp. These guys can make butyric acid, which smells and tastes of a mix of parmesan cheese and vomit.
2. Enterococcus faecium. This bacteria can make bioactive amines, which some people are severely allergic to. Moreover, these amines are often quite unpleasant, and are what give shit and corpses (among other things) their unique odours.
3. Bacillus sp. (most often Bacillus ereus, clausii, and pumilus) make diacetyl (butter) and may also make bioactive amines.

Clearly, we don't want t be dumping any of the above guys in our beer!

EDIT/UPDATE: Stefan Wiswedel has done some experiments looking at probiotics containing amylases (which break down starches/dextrans) and protinases (which degrade proteins) along side the usual probiotic bacteria. Turns out using these is a bad idea - it kills the body and flavour of the resulting beer. Stefan has posted additional details in the comment section, below.

---

A Simple Rule of Thumb

So that's a lot - but a good rule-of-thumb is to limit yourself to probiotics that contain only Lactobacillus species, which is easy to remember when you're at the store. 

But if your memory is better than mine, than any probiotic with Lactobacillus sp. plus any of Bifidobacteria sp., Streptococcus thermophilus or Leuconostoc sp. will be good as well.

And if the probiotic contains anything but the above 4 groups of organisms, I'd recommend you stay away.