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Blinded by Science: Wild Fermentations!

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July 31, 2015 by fhsteinbart


Here we see a pair of yeast cells budding with the evidence of previous daughter cell budding scars being shown.

Here we see a pair of yeast cells budding with the evidence of previous daughter cell budding scars being shown.

After several customers have asked me about wild or spontaneous fermentation, I decided a little light needed to be shed on the subject.  Traditionally, spontaneously fermented beer is sour mashed overnight then finished the next day by boiling with stale hops.  Then the beer is pitched with either house yeast or left open in cool ships (wide shallow fermenters) to pick up atmospheric wild yeast and bacteria.  Frequently after fermentation the beer is allowed to age in old oak barrels acquiring the flora and fauna as found in the oak.

Anatomy of typical Lactobacillus bacteria.

Anatomy of typical Lactobacillus bacteria.

Besides saccharomyces cerevisiae, the yeast commonly used in beer and wine, you’ll also find Brettanomyces with its earthy leathery notes, Lactobacillus with its traditional lactic acid tartness, Pediococcus with its usual production of lactic acid and diacetyl.  Acetobacter, the principle producer of acetic acid as found in vinegar which gives the hard sour of Lambics their particular character.  What is most common in the production of these beers is blending fresh beer with aged beer to achieve a particular flavor profile as desired by the brewery.

Here we see Acetobacter reproducing by binary fission.

Here we see Acetobacter reproducing by binary fission.

The base ingredients for most sour beers is fairly straightforward with the paler beer principally being made of Pilsner Malt, and unmalted wheat using the previously mentioned stale hops with mother nature being left to finish the beer.  The darker beers will use coloring mall such as crystal malt, chocolate malt, or black malt, to achieve the proper color and flavor profile that the brewer wants in the beer.

A single cell of B. Bruxellensis, the most common form of Brettanomyces or the "British Fungus".

A single cell of B. Bruxellensis, the most common form of Brettanomyces or the “British Fungus”.

Aging of the spontaneously fermented beers frequently occurs in the presence of oak for an extended period of time from 1 to 3 years.  Brewers of these beers frequently isolate wild or spontaneous fermentations from normal control fermentations in order to prevent cross contamination.  If there’s a choice between fermenting in glass or plastic it is highly recommended to use glass.  If plastic is chosen for whatever reason please make sure to properly label that plastic fermenter as having contained wild yeast and or bacteria.  To prevent cross contamination from occurring a home brewery a method that I have discovered works quite well in sanitizing any equipment that comes in contact with spontaneously fermented beers.

Oak barrels for as far as the eye can see! Who wouldn't want to have this for their cellar?

Oak barrels for as far as the eye can see! Who wouldn’t want to have this for their cellar?

This is a three step process which starts with thorough cleansing to eliminate visible detritus followed by an overnight soak in a weak bleach solution (1 tablespoon bleach per gallon fresh water) to sanitize those organisms sensitive to sodium hypochlorite and calcium hypochlorite.  The next day, after emptying the fermenter and rinsing it several times you then add a 25 PPM charge of Iodophor to the entire volume of the container overnight once again.  After another 24 hours, drain and rinse the fermenters several times again before proceeding to the final sanitization step.  Fill the fermenter with cold clear water and add an appropriate amount of Star-San, allowing the Star-San to remain in contact with the fermenter for a minimum of 15 minutes to finish the sanitization process.  While it may seem extreme I’ve found the above referenced method of sanitization to completely remove wild yeast and bacteria from the surfaces of my fermenters.  While sour beers aren’t for everybody, for those intrepid enough to enjoy these beers to make them themselves the reward is substantial enough to go through the mechanics of production, aging, and packaging.

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