The Rare Barrel
December 20, 2017 | The Rare Barrel

Terminal Acidic Shock and Sour Ale Bottle Conditioning

Here at The Rare Barrel we bottle condition all of our bottled beers. While bottle conditioning can be a little more challenging that force carbonation, we believe that this is an important step for creating the best flavor profile.  In short, bottle conditioning means that we add a simple sugar (Dextrose) and new dry yeast to a beer before packaging. And then we wait… A new fermentation occurs in the bottle to carbonate it, this also adds a richness and body that we are fond of.
Unfortunately, most yeasts do not perform optimally at a very low pH or at a high alcohol content. In the past we, along with other breweries that bottle condition sour beers, have had issues with inconsistent and under carbonated conditioning results. Even experiencing batches where carbonation nearly completely fails. This is obviously an incredibly disappointing incident, we love the beer we make and we want you to experience the best presentation of our beer.  As Quality Manager, I wanted to help overcome this issue. After doing a bit of research on yeast shock and speaking with a few breweries, we created a protocol to improve consistency in carbonation and bottle conditioning.

What is Terminal Acidic Shock (or TAS)?

Terminal Acidic Shock refers to the death or dormancy of Saccharomyces cerevisiae during fermentation in a high acidity and high ethanol content environment (Rogers To combat this many breweries will temper a yeast addition slurry with a portion of the beer to be carbonated. This allows the yeast to slowly adjust to the severe conditions and have a few generations of growth within a few steps to increase the productivity once pitched into the beer and bottled.

The Experiment

To test different mediums and processes I created an experiment where I took the dry yeast and hydrated it with a sugar solution.  A few different types of low sugar content solutions were tested in this experiment including wort and varying sugar water concentrations. After adding the same amount of yeast to every sugar solution I allowed 2 days for some growth and fermentation. I then added a 50:50 solution of more low sugar solution and sour beer and waited another 2 days. I then tested cell viability and density as will as pH and gravity changes. I concluded that a 2 degree Plato water and dextrose with nutrient added yielded the healthiest yeast at the end of the beer tempering. The slurry was then added to a small bottling run. I also compared this experimental slurry to a control of just day-of rehydrated dry yeast which was our current method of yeast preparation. I concluded that the tempering increased yeast health and decreased conditioning time (tested by yeast viability and pH/gravity changes).
*QA/QC Manager Jenna Blair counting cells of Saccharamyces and Brettanomyces mixed cultures under a microscope.

Our New Procedure

We now boil dextrose and water with a small amount of yeast nutrient to a vessel cool to an optimized fermentation temperature, add yeast and allow for 24 hours of fermentation, then add a 50% 2 Plato sugar water and 50% beer solution the day before bottling and count the yeast each day during tempering in order to assure the yeast we pitch is healthy. On bottling day we add sugar to the beer which is calculated based on the desired CO2 volumes and then count the slurry of tempered yeast and pitch by weight for a goal of 2 million cells/ml. This may seem like a lot as it is far over what would be recommended for a pale ale but for sour/barrel aged beers even with the tempering 1.5-3 mil cells/ml is recommended.
*Weighing dextrose before adding to boiling water.
Scaling this experiment up to our needs was interesting, anyone who we had known that had tried anything like this had small enough bottling runs where the liquid and yeast additions could all be contained in a small flask! We adopted the procedure to yeast brinks converted from full half barrel kegs and eventually into our 5 barrel fermenter for our largest bottling batches.
* Top Photo: Cellar Technicians weigh dry yeast that will NOT be added to the dextrose mixture to ensure that the yeast added is not contaminated.
Bottom Photo: Yeast starter after dry yeast has been added to the dextrose mixture prior to transfering to a brink 24 hours before bottling day.
Though not without challenges we have experienced favorable results with this procedure. We have seen shorter carbonation times as well as more bottle to bottle consistency. We are however continuously tweaking the procedure. We plan to play with different liquid addition volumes and sugar water to beer rations as well as pitch rates. Our goal is first and foremost to make good beer, we get to accomplish this by continuing research and experimentation not only in fermentation and blending but also by conducting experiments that can streamline process and improve the quality of our product.
Consistency and predictability are often regarded as some of the pillars in beer quality assurance and control. Sour beer is a beast that refuses to be controlled but with continuous experimentation we are enthusiastically working towards higher caliber beers.
If you have any questions, feel free to comment below.
Jenna Blair
QA/QC Manager

Rogers, C. M., Veatch, D., Covey, A., Staton, C., & Bochman, M. L. (2016). Terminal acidic shock inhibits sour beer bottle conditioning by Saccharomyces cerevisiae. Food Microbiology,57, 151-158. doi:10.1016/



Shawna's Gravatar
@ Dec 20, 2017 at 10:58 AM
Thank you for sharing. For someone who just has a home lab it's helpful to see the insight that goes into a larger production.

Rob Lovatt's Gravatar
Rob Lovatt
@ Dec 21, 2017 at 2:17 AM
Hi Jenna,

Great article!

We have always used champagne yeast here, which has performed relatively well.

Can I ask what PG you generally bottle at? Sometimes I have encountered sour beers a stubborn PG which even with time and plenty of Brett won't drop.

Steven Trentham's Gravatar
Steven Trentham
@ Dec 21, 2017 at 7:25 AM
Quick question. I have read on the milk the funk that acclimating the yeast with some sour beer and Apple juice mixture is a reasonable option. What is your opinion? Also, as a homebrewer which yeast strain would be reasonable in your opinion? Cbc1, wine yeast? Thanks for your time and info.

Adam Young's Gravatar
Adam Young
@ Dec 21, 2017 at 8:17 AM
Cool blog - thanks! Did you guys ever go with a "champagne" yeast, or is that one you'd avoid due to potential flavor impact? That's what I've used for my sours at home, and I'm curious if I'm making a mistake by potentially adding flavor dimensions to the beer I hadn't thought of. I feel that yeast has been pretty tolerant of pH and ABV and I thought it seemed neutral enough - would be good to get a pro brewer's take on that.

Matt Bochman's Gravatar
Matt Bochman
@ Dec 22, 2017 at 6:11 AM
I'm glad to see that the yeast adaptation is working for you and that you've been improving on the process! We've had lots of good feedback from brewers all over on this new (?) way to prep yeast for bottle conditioning.

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