There are many different variables throughout the fermentation process that affect how sour beer is produced. In order to better understand our beers and sour beer production in general, we pull small samples from each batch of beer every 10-14 days and specifically track four things: sensory, attenuation, temperature, and pH.
In order to test each batch, we pull a very small sample of beer from the barrel. However, it is incredibly important that we do not allow extra oxygen in the barrel, so we never remove the bungs from the barrel during this process. Instead, we are able to get samples from our barrels by “pulling nails” (often referred to as the “Vinnie Nail”, popularized by Vinnie at Russian River). It’s as simple as it sounds… we grab a pair of pliers and a glass, pull the nail, catch the sour beer as it pours out of the barrel, and then put the nail back in the hole! While sampling is important for testing the beer, it is important not to remove too much beer from the barrel at one time as that could also cause too much oxygen to enter the barrel.
After samples are pulled, our production team first tests the beer on sensory. With over 900 barrels filled, we are sampling sour beer every day. Sight, smell, taste, and mouthfeel of each sample are recorded to assist us in tracking the progress of our different yeast and bacteria experimentations as well as help create exciting new blends. We’ll take notes on how each batch looks, smells, and tastes every 10-14 days so that we can track how it changes over time and know when it has completed fermentation.
Are there still fermentable sugars in the sour beers? Are the yeast and bacteria still fermenting the beer? To answer these questions our production team uses an Anton Paar to measure attenuation and monitor the progression of the fermentation process. The data collected from these readings, show us how much sugar has been converted into alcohol and carbon dioxide over time. If we see weeks of stable readings, we know that yeast and bacteria have fully attenuated the beer and that this batch of beer is either ready to be packaged or blended. Ensuring that our beers have fully attenuated and are fermented dry is very important to make sure that our beers do not over-carbonate in the bottle.
Temperature plays a very important part in yeast and bacteria activity. Yeast and bacteria typically convert more sugar into alcohol and carbon dioxide in hotter temperatures, while fermentation can slow down in colder temperatures. Since the amount of heat present affects how yeast and bacteria act, it also affects how sour beer tastes and smells. Different fermentation temperatures will produce different esters and phenols, which give each batch of beer varying characteristics. The ideal temperature range is somewhere between 50-70F, which is actually one of the main reasons why we decided to start here in Berkeley. Berkeley’s climate hovers in the ideal fermentation temperature range. The size and location of our warehouse provide an excellent space to house our 100 BBL fermentors and over 900 barrels filled with fermenting beer.
The final assessment that we record every 10-14 days is pH level. pH is the measure of how acidic or alkaline a solution is. Bacteria produce acids (most commonly lactic and/or acetic acid), which acidifies our beers and puts the “sour” in them. We track the progress of acid producing bacteria by taking a pH reading. Bacteria are still active if pH continues to decrease, but after consecutive weeks of stable readings we are able to proceed in the blending process.
How do we test pH? First, we calibrate a probe to 7.0 pH by dipping it into a neutral storage solution. We then rinse the probe with water and dip it into the second acidic storage solution to calibrate the probe to 4.0 pH. We rinse the probe one more time with water and then dip it into our beer sample to take a final pH reading.
pH will give us a good idea of how acidic a beer is, however, it doesn’t directly translate to how people perceive acidity on their pallet.
Recording the data from these four assessments allows us to further our understanding of how yeast and bacteria work to create sour beer. We learn more and more as we track each batch of beer in this decades long experiment.