An Overview on Fermentation at The Rare Barrel
What is fermentation?
Yeast and bacteria and where we get them
Scaling up! Stages of fermentation at The Rare Barrel
Fermentation also occurs during our bottle conditioning process
Thanks so much for the post! I was curious about your process of bottle conditioning. When you guys have decided that the uncarbed beer has reached terminal and is ready to go into the bottle, do you calculate cell counts for YEAST additions when moving onto conditioning, or is it only pertinent to measure the sugar because there will already be enough active yeast before bottling?
Thanks for any insight!
Heterolactic cultures produce acetyl phosphate, which is anaerobically reduced to ethanol; or, in the presence of oxygen, is reduced to acetic acid. As you probably guessed, this isn't the only pathway to acetic acid in our beers -- other microflora we use have the potential to create acetic acid as well. In addition to the heterofermentative Lacto, perhaps the most prominent acetic acid producer at our brewery is Brett Drei. In the early days most of our beers were made with Drei, and we learned quickly that the barrels would have a limited shelf-life, after which we would be on the lookout for acetic acid or ethyl acetate (perfume / nail polish).
Admittedly, as barrels are actually porous and get moved around with a forklift, we cannot entirely eliminate exposure to oxygen, but we have developed some strategies: First -- we track and know the ages of all our barreled beer, as well as the attributes of the cultures that we've worked with. If we have a batch that has a large proportion of Brett Drei, we know that the sweet spot for those barrels will be 8-10 months after brewday, so we look to blend those for package or further aging before they hit the danger zone. If a batch has a low flocculating saison yeast, hopped wort, and a diverse mixed culture of Sacc, Brett, and Bacteria, we know it may be more stable over a longer period. Second -- we purge, purge, purge with CO2. We purge our tanks and hoses before racking. We purge barrels before filling. We push our beer with CO2. We have CO2 flowing into the tank when we fruit. Third -- when adding fruit to a beer, and when moving a beer to barrels, we like to have some amount of active fermentation occurring. Lately when we fruit a beer we will rack actively fermenting beer from a recent brew into the tank to "attack" the fructos and take up any oxygen that might have snuck in. Ideally these beers will have healthy Brett, which is known for its oxygen scavenging abilities. Fourth -- we bottle condition. Refermentation in the bottle aids in taking up any oxygen that might have snuck in during the bottling process.
I'm sure I can come up with other strategies we employ, but I think you get the gist. Thanks for reading!
Hi Ben -- We have not kettle soured any of our beers. We use stainless steel totes to transport chilled wort from a brewery to our fermentation facility. Once here, we pump into our conical fermenters and ferment with whatever microbes we have chosen for that batch. Sometimes we will start with saccharomyces or brettanomyces by itself, sometimes sacc and brett, and sometimes a full mixed culture with bacteria. The beer sits in stainless for a little over a week, and then is transferred to barrels. Typically the beer has been inoculated with souring bacteria by the time it hits the barrel, but it still takes a few months in the barrel for tartness or sourness to develop.
Hello Taylor -- We do not have a particular house character that we target or blend toward--rather we try to combine batches and blends to create the best beer that we can. It’s difficult to attribute characteristics of our beers to a single variable such as mash temp, microbes, etc.; but these are all variables we look at when brewing to create new flavor and aroma profiles. Over the last year and a half or so our yeast and bacteria “portfolio” has increased dramatically, and we have also been developing a number of new techniques. Most releases since mid-2016 include multiple strains of sacc, multiple brett strains, and numerous lacto and pedio cultures -- this is a trend you will continue to see from us going forward. Another variable that we have been intensely experimenting (with great results) are hopping rates and times. Also, what I call “staggered pitching”, where we add additional microbes after primary fermentation has subsided. The only overarching “house character” that we target is “sour”, and even then we try to remain intensely vague in our definition of what that means.
Hello AJ and Jerad-- I thought I’d address both your questions together as they both pertain to our bottling procedure. We have a few metrics we use to determine the suitability of a beer for packaging, including fermentation trends, gravity stability, and finishing gravity. We also pay attention to pH, which can drop without affecting gravity, letting us know that homofermentative bacteria is still in play. Most importantly we rely on sensory evaluation. At times all instrument-derived indicators might suggest a beer is stable, but it just doesn’t taste or smell ready. This is particularly important in beers refermented with fruit, or soaking in spirit barrels, etc. When we determine that a beer is ready to package, we will rack the beer to a brite tank to get a more precise volume, and calculate our bottling sugar and yeast additions off of that measurement. We target anywhere from 2.2 - 2.7 vols CO2, depending on the beer. All calculations only account for the yeast we add for bottling -- we don’t rely on any residual yeast from primary or secondary fermentation. We currently use Maurivin Platinum as our bottling yeast, but are in the process of trialing other yeast to see how they might affect specific bottled beers.
Hey Mike! Great to hear from you -- Hope all is well in upstate! Hit me up if you’re in the Bay Area -- I’d love to catch up.
We don't cold crash at The Rare Barrel, except to force carb & keg - any yeast (saccharomyces or brettanomyces) in suspension goes into the barrel. Because our beers have brett in them, and go through a long, slow secondary fermentation, we aren't too worried about (and haven't experienced) any autolysis related off-flavors. My understanding is that any sacc that might die or go dormant during this secondary aging period essentially become a nutrient source for the brett.
I'm not sure if or how bacteria interacts with dead or flocc'ed sacc cells. That might be something interesting to look into, for sure.
Great post and great answers, thanks!