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 et.al.) 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.
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.
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/j.fm.2016.02.012