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The Rare Barrel
December 20, 2016 | The Rare Barrel

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


Time Posted: Dec 20, 2016 at 8:00 AM Permalink to An Overview on Fermentation at The Rare Barrel Permalink Comments for An Overview on Fermentation at The Rare Barrel Comments (13)
The Rare Barrel
November 8, 2016 | The Rare Barrel

Crowd-sourced Collaboration Between Yazoo Brewing Company and The Rare Barrel

We're excited to announce that Brandon Jones​ of Yazoo Brewing Company​ is teaming up with us to work on what we're calling a "Crowd-Sourced Sour" collaboration!! That means we're opening every part of the process to share with the public, mainly through The Sour Hour and Milk The Funk​!

Brandon will be on The Brewing Network's The Sour Hour tomorrow (Wednesday) at 5 PM PST and we'll definitely be chatting about this project along with drinking some of his latest creations.

Our main goal with this project is to drive discussion of sour beer making techniques and philosophies. From brew day, to fermentation and aging, and all the way through packaging, you'll be able to not only follow the process with unprecedented access, but actually be able to influence the final outcome of the beer! We know this beer will be a Logistical Nightmare (<-- good beer name!), but the value of collaborating in this manner is to learn from the diverse opinions and knowledge of the sour beer community, pro brewers and home brewers alike!

For more details, you can follow this on @YazooBrew, @TheRareBarrel, @embracethefunk, Milk The Funk, and The Sour Hour by searching #SourCollab!
The Rare Barrel
March 2, 2016 | The Rare Barrel

Barrel Samples: sensory, attenuation, temperature, and pH

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.

Pulling Nails

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.


Time Posted: Mar 2, 2016 at 9:00 AM Permalink to Barrel Samples: sensory, attenuation, temperature, and pH Permalink Comments for Barrel Samples: sensory, attenuation, temperature, and pH Comments (4)
The Rare Barrel
September 21, 2015 | The Rare Barrel

The Sour Hour Podcast

Do you like learning about sour beer? If so, you might enjoy The Sour Hour podcast on The Brewing Network!

The Sour Hour is a podcast made for sour heads, homebrewers, and professional brewers who are interested in spreading knowledge sour beers.  The show is hosted by Scott Moskowitz of The Brewing Network and Jay Goodwin from The Rare Barrel, and they are usually joined by special guests on each episode.

The Sour Hour is available for free through iTunes! If you have any questions you’d like Jay and Scott to answer on the show, feel free to email your questions to or call 888.401.BEER when they are in the studio!

Here is a list of episodes and special guests that are available at the time of this blog post…

Episode 1 – Michael Tonsmeire, author of American Sour Beers

Episode 2 – Lauren Salazar of New Belgium

Episode 3 – Cory King of Side Project and Perennial Artisan Ales

Episode 4 – Troy Casey of Casey Brewing and Blending

Episode 5 – Tim Clifford of Sante Adairius Rustic Ales

Episode 6 – Q&A Episode

Episode 7 – Nick Impellitteri of The Yeast Bay

Episode 8 – Chad Yakobson of Crooked Stave Artisan Beer Project

Episode 9 - Q&A Episode

Episode 10 – Rudi Ghequire of Rodenbach Brewery

Episode 11 – Jean of Cantillon, Vinnie of Russian River, and Rob and Jason of Allagash

Episode 12 – Jim Crooks of Firestone Walker Barrelworks

Episode 13 – Milk The Funk

Episode 14 – Adrienne Ballou and Garrett Crowell of Jester King Brewery

Episode 15 –Jester King continued 

The Rare Barrel
August 5, 2014 | The Rare Barrel

Echo Series: an experiment with un-rinsed barrels

We like to experiment here at The Rare Barrel, and sometimes those results are not only worth tasting, but also worth writing about. One of these experiments that we have been working on is called the Echo Series.

In short, the Echo Series is an experiment where we let the yeast/bacteria/beer and sometimes fruit from one barrel, influence the fermentation and flavors of the next sour beer to fill up that barrel. In order to fully understand what we are talking about though, we’ll give you a little more back story.  

When one of our sour beers has finished barrel aging and is ready to be packaged, we will transfer most of the sour beer from each barrel into the blending tank.  With the help of a sight glass, we continue to  remove most of the sour beer from each barrel, and stop removing the beer when  we start seeing yeast, bacteria, and sometimes fruit in the sight glass. We then leave the remaining mixture of beer, yeast, bacteria, and fruit in the bottom of the barrel, which is typically about a few inches of liquid in the bottom of the  barrel.. Typically we would rinse the barrels before refilling them, however, with the Echo Series we fill the barrel with another sour beer without rinsing out the previous remnants and let the refermentation process begin. This means that there are still millions of cells of yeast and bacteria  transferred over to the next beer… the same yeast and bacteria that have already proven themselves to create a great tasting beer!

Hypnotized, the first beer to be released in the Echo Series, is a red sour that aged in barrels that were previously used to age Ensorcelled (dark sour beer with raspberries). With Hypnotized, we noticed a few significant differences between that beer and its counterpart that we aged in rinsed barrels. Firstly, we found that Hypnotized finished attenuating faster and had a cleaner character (free from off-flavors normally seen in sour beer making) than the same red sour beer aged in rinsed barrels.  The more advanced yeast and bacteria that did a great job fermenting Ensorcelled seemed to really help give Hypnotized a terrifically balanced acidity while being clean and highly drinkable. Additionally, we noticed that it picked up a very subtle raspberry character from the un-rinsed barrel, which added another layer of complexity to the flavor profile.

Hypnotized (Echo Series) is our first release in this series. Needless to say, we’re pretty excited about our continued experimentation with re-using advanced yeast and bacteria from the oak. We have a few more Echo Series beers in the works, and look forward to sharing them on draft in the near future.




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