Q: Dear Brewmaster,
I am the brewery lab manager at a brewery and we are reusing our main yeast strain, A56 (from BSI). We are having an issue with the storage conditions that I cannot figure out. Here is our process:
We ferment a 15 or 30 bbl fermentor at 70 F, we drop the temperature down to 60 F once it has reached terminal gravity in order for the yeast to settle. The next day we collect the yeast from the cone using proper techniques (we drop trub) and then fill corny kegs using pressure and the quick disconnect in order to keep a closed system. We purge these kegs with CO2 before filling with yeast. We only fill these kegs 3/4 full with yeast and I attempt to degas them. I will shake the kegs and use the PRV on the keg to remove excess pressure but sometimes I cannot remove all of it. We put the kegs in a cooler set to 34 F. I will allow the kegs to cool down for a few hours and again degas. If I can degas the keg, I will put a disconnect and blow off tube on the "in" portal and will put the end of the tube in sanitizer. I will leave the kegs and check on them 24 hours later. Everything looks fine, no pressure builds up and the sanitizer is clean. Then I come back 48 hours later and I have a mess of yeast that has poured out of the blow off tube. WHY? As far as I know the chest freezer is always at the appropriate temperature and I make sure of that. Other times, I am unable to remove all pressure from the kegs no matter what I do.
Our brewery is small and corny kegs are the most practical option for us right now. What can we change in order to not continue to lose yeast?
Thank you for your time and I look forward to your thoughts.
A: There are several possible contributing factors and process adjustments here:
1. Hold fermentation temperature for 24-48hrs after terminal gravity prior to cooling. In addition to other benefits (ie VDK removal) this will help ensure that you are not leaving fermentable extract behind; one possible cause for what you are experiencing.
2. You mentioned that no pressure builds after 24 hours, but is it possible that the port is actually clogged with yeast from shaking? I do not recommend shaking the keg. You'll have better results/less mess with a slower, gentler degassing process. Try placing the keg in the cooler as soon as it's filled. Instead of shaking the keg, bleed the head pressure and immediately airlock the keg. Alternatively, bleed the head pressure periodically (without shaking) and skip the airlock altogether. You don't need to accomplish 0 psi in the headspace, you just want to avoid excessive pressure in the keg (for your safety and to avoid unnecessary yeast stress).
3. Yeast is a great insulator, so kegs of yeast will not cool down quickly. The outside may feel cool, but may not be a good indicator of the temperature inside. You may have a great reason for only cooling to 60F at harvest (ie a warm dry hop process). If not, you might consider additional cooling in the FV prior to harvest. This would result in thicker slurry and cool the yeast much faster vs. a corny in a chest freezer.
4. Choose a better container. Corny kegs are notoriously difficult to clean & sanitize and make for risky yeast storage. Several vendors sell half bbl kegs with 4" TC fittings for a few hundred dollars.
Ensuring the yeast isn't entrained with fermentable extract, slow & steady (or limited) degassing, better cooling, and a better storage container would go a long way towards avoiding mess and optimizing storage conditions for your yeast. Whatever vessel you use, please be sure it has adequate pressure relief safeties. By the way, none of the following articles reference yeast storage in kegs, but here is some good further reading on the topic of yeast storage: