An Overview on Fermentation at The Rare Barrel

Hello internet! As the Research & Development Coordinator at The Rare Barrel, my role is to track our beer from the day it is brewed until it is packaged, ensuring that barrels are harvested at the correct point and that we always have beer to blend, fruit, or package. I also aid in blending, and work to develop new approaches and procure different yeast, bacteria, and secondary additions for our sour beers. I’ll provide a brief intro to what fermentation is, how we procure the yeast and bacteria to make our sour beer, how we attend to the different stages of sour beer fermentation, and how we use fermentation to carbonate our beers.

What is fermentation?

Beer fermentation is all about yeast and bacteria converting grain-derived starches and sugars into alcohol, CO2, and other flavorful and aromatic compounds, including acids. Different yeast and bacteria perform this task uniquely, and the species and health of the organisms greatly affect the end product. A primary difference between sour beer and clean beer is the use of bacteria in this fermentation process. Bacteria such as Lactobacillus and Pediococcus are able to convert starches that yeast cannot, and a byproduct of these conversions are a bulk of the acids that make our beer sour.

Yeast and bacteria and where we get them

The Rare Barrel is unique in the number of different yeast and bacteria that we use. In addition to using single strains of Saccharomyces cerevisiae from many diverse brewing traditions (Belgian, French, English, American, etc.), we also use a wide variety of Brettanomyces yeast (claussenii, brux drei, lambicus, anomala, brux, etc.), Lactobacillus (brevis, delbrueckii), and Pediococcus (damnosus). Like most commercial breweries, we procure most of our microbes from commercial yeast labs (we work with several). At times we will pull barrels we like from our cellar and use those as inoculants. Occasionally we will get a pitch of yeast from another local brewery (yeast can get pretty expensive, and swapping yeast is a relatively common practice in the brewing industry). We also have a few cultures that have been grown up from the dregs at the bottom of some of our favorite commercial bottles. Propagation from bottles is done in a very homebrew fashion, where we carefully “decant” (and drink) the beer sitting atop the dregs, and add a small amount of sterile wort to the bottle. We then gradually step this up into a 5 gallon carboy, then a 15 gallon brink, our 5 BBL project fermenter, and then into a 30 BBL batch.

There are a number of different ways that we approve microbes for production, and there are no hard-and-fast rules here. Jay draws on his experience at The Bruery, and his four years guiding the program at The Rare Barrel. A number of us in production are avid homebrewers, and have extensive experience with many different strains and conditions, so we definitely have opinions. Additionally, we have a “menagerie” of about twenty different microbe blends at The Rare Barrel, kept in flasks and carboys with our wort. Tasting and evaluating these samples in a democratic fashion drives some of our decisions as to what should be trialed at a larger scale.

Scaling up! Stages of fermentation at The Rare Barrel

While we have done a few experiments with primary fermentation in barrels, we start nearly all of our fermentations in our stainless conical tanks. It varies whether primary fermentation will be performed by a single strain of Saccharomyces, multiple Saccharomyces strains, a blend of Saccharomyces and Brettanomyces, or a full mixed culture with numerous strains of Saccharomyces, Brettanomyces and bacterias. Our wort is produced off-site, transported in stainless totes to our facility, and then pumped into our fermenters past an oxygenation stone. Active fermentation produces a fair amount of heat, and depending on the yeast we may decide to control fermentation temperature with the glycol jackets, or to simply let the temperature “free rise.” Fermentation temperature plays a very important role in driving different alcohols and esters, phenols, and other precursors for biotransformation during secondary fermentation.

After primary fermentation subsides (about a week or so), we will transfer the beer to oak barrels. Sometimes we will add an additional inoculant to the beer prior to racking out of the tank; in other cases we will rack onto a slurry of yeast and bacteria from past batches; and in others we will rack without further amendation into rinsed, steamed and ozoned barrels. This decision is typically made by looking at our “cellar balance” and deciding where the project fits -- whether it is intended to be a portion of a particular blend or brand, or if we are just adding to the variety of our blending stock.

After the beer is in barrels, we monitor and wait. I guess we’d call this the “secondary fermentation” phase, where the microbes that function on longer timelines (typically Brettanomyces and the bacterias) are doing most of the work, and the beer is gradually souring. We track gravity and pH on most of our batches on a monthly basis, although some get tested weekly to ensure all is well. We are getting pretty good at predicting when a particular batch will be ready to harvest and either fruit or blend for a final product. If the beer receives a sugary secondary ingredient (fruit, for instance), it will be returned to the barrel with a shot of fresh yeast for another round of fermentation, where we monitor and wait once again.

Fermentation also occurs during our bottle conditioning process

While we “force carb” our draft beers in a brite tank using a CO2 stone, all of our bottled beers are naturally carbonated in the bottle. This means (you guessed it) more fermentation! Prior to bottling, it is essential that all active fermentation processes have come to completion, and the beer is absolutely stable with no residual sugars remaining. To carbonate our bottled beer, we add a calculated solution of dextrose and a yeast--just enough to add the level of carbonation that we target. If there were any sugars remaining in the beer, carbonation would increase potentially leading to gushers or even bottle-bombs. We are extremely cautious with packaging, and it is not unusual to delay bottling if we notice an anomaly.

After bottling, we allow the beer to rest and re-ferment for a minimum of 9 weeks before it is put up for sale. We have weekly check-ins on the progress of the conditioning, and will delay a release if we notice anything out of the ordinary. Bottle conditioning is a fermentation process, so the beer does go through some of the same phases that we notice in primary fermentation, although because dextrose is such a simple sugar it is consumed at an increased rate.

Our beers continue to evolve in the bottle even after they are a packaged. The yeast and bacteria that were present in primary and secondary stages of fermentation--especially Brettanomyces and Pediococcus--remain active and continue to slowly transform the more difficult to digest starches, creating new flavors, aromas and textures. While bottles are certainly ready to drink when we release them, they are a living product and change over time.

I hope this provides an interesting glimpse into how we think about the various stages of fermentation at The Rare Barrel. Post up any comments you might have and I’ll be glad to follow up on any questions!

Stay Sour!

Aaron M. Wittman

R&D Coordinator