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Master Brewers Association of the Americas > BREWING RESOURCES > Ask the Brewmaster
May 14
Yeast Storage in Corny Kegs?

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:

April 08
Off-flavors from Peracetic Acid (PAA) Residual?

​Q: I have a question about sensory change of beer. One of the sanitizers is POAA(Peroxyactate) which is known as no-rinsing sanitizer. Even though CIP is done including final rinsing after POAA step, is there any possible that residual POAA can change beer flavor? I checked beer sensory which described as burned rubber. It is not sure but certainly it is off-flavor. I guess, one of direct causes is that residual POAA is mixed with beer after CIP step and stored for 5days. That may change beer chemistry. Please let me know any possibility making sensory change using POAA for sanitizer. Or help me to find any resources related with no rinsing sanitizer. Thank you.​

A: Peracetic Acid (AKA Peroxyacetic Acid or PAA)​. PAA is the preferred no-rinse sanitizer in many breweries. One of the main reasons for this is the absence of off-flavors when used properly. I've used PAA extensively in small and medium size breweries, but I reached out to MBAA members Steve Gerloff (Madison Chemical) and Dana Johnson​ (Birko Corporation) for some background on how PAA works and its potential for off-flavors. As you might expect, they both had plenty of interesting information about PAA. I've included a few highlights from Steve here:

PAA is an equilibrium of peroxyacetic acid, acetic acid, and hydrogen peroxide. The method of sanitation is accomplished by way of its oxidative potential; free oxygen attacks and kill microorganisms, fungi, yeast, and bacteria. Directions for proper use call for no rinse and time to allow the surface to air dry. 

One of the main features of PAA is that it completely breaks down to water and carbon dioxide. The rate of this disassociation depends on the concentration of the solution. Normal dosage rates range from 100-200 ppm (although some companies recommend stronger concentration levels). In a 100-200 ppm range the disassociation should be complete within a couple of hours, but can be sooner given ambient temperatures.

That said, introduction of product immediately upon application could unintentionally oxidize product. In terms of sensory evaluation the typical oxidation profiles aromas etc. could be picked up on a panel.

This could be encountered on improper purge on a keg washer where a small residual would come in contact with product when the keg is filled immediately after cleaning.

Personally, I’ve only had one experience where an off-flavor was clearly attributed to PAA. In that particular case a filler operator failed to dump all PAA from the bowl following startup SIP. The beer had a strong acetic acid (vinegar) flavor, which was noticed by all tasters at startup. The filler bowl was then dumped and refilled with new beer from the BBT. This resulted in a true to brand flavor profile with no perceived acetic acid notes.

Here is some information on degradation via Dana:

What is the impact of Peracetic acid products on the environment?
Peracetic acid products are environmentally responsible. The short half-life means that PAA is not persistent and rarely needs to be neutralized prior to discharge. No additional conductivity is introduced to the receiving waters. The results of a large aquatic toxic toxicity study (available on this web site) demonstrate PAA is far less toxic to marine and fresh water organisms than alternative disinfection chemistries. If spilled or applied to soil, PAA decays in a few minutes with no lasting impact on the soil quality. The ultimate end result is carbon, oxygen, and water.

Here are some great MBAA resources relevant to your question:


March 30
Dry Hop lbs per bbl
Q: Hello!  I'm looking for some reference regarding dry hopping quantities regarding to style. Something that would guide me in lbs/barrel. Thanks

A: The rate of hops used per barrel for dry hopping depends on quite a few variables. Some to consider: 
  •  Hop variety & type of hop product used 
  •  Hop oil content
  •  Condition/age of hops to be used
  •  Method of dry hopping (slurry, recirculation, stirring, static bags, torpedo, etc.)
  •  Contact time
  •  Temperature during dry hopping
  •  Presence of yeast/stage of fermentation

With so many different approaches to dry hopping and process variables, it is not possible to give a 1-size fits all answer per beer style or brewery. Furthermore, what is the desired outcome – to maximize aroma, flavor, or both? 

I recommend starting with 1-pound per bbl. Assuming a good process (get rid of that O2!) a 1-pound per bbl dry hop is sure to give you some good aroma extraction. If your process is efficient, you may be able to achieve good results at a much lower rate (< half a pound per bbl). Note that many brewers have experienced diminishing returns; 2 pounds per bbl will not yield double the aroma.

Here are some great MBAA resources where you can learn more about dry hopping:

Happy hopping!
December 30
Hop varieties for dry hopping

​Q:  I'm brewing a blonde ale, all grain. I used Crystal hops for the 40 min, 20 min, and the last 5 min boil. Should I continue using Crystal hops for dry hopping? Or should I use Cascade hops, or a mix of both?

A:  For dry hopping, any of the three options are acceptable depending on what aroma/flavor attributes you desire in the beer. Crystal will contribute a spicy, flowery, slightly citrus aroma. Cascade will contribute a flowery or citrus (grapefruit) aroma. Most brewers have found that using a blend of hop varieties for dry hopping offers more depth and complexity in addition to increased flexibility due to supply and availability issues.

November 26
Warming Calculations

Q: I'm looking at initiating a can conditioning program. We are planning on filling the beer cold (~32–34°F). I will need to warm it up from the filling temperature to 65–70°F in order to initiate conditioning fermentation in the can. I need to calculate how long it will take to warm it through a "warming tunnel" given the ΔT and the temperature of the water used to warm it (~125°F). The can volume is 16 oz., so how much residence time will be needed to get the beer into the desired temperature range?

Also, if we wanted to build a warming table—i.e., an accumulation table that could hold an inventory of cans that slowly move under a hot water shower—how do I calculate how big to make it if I am running at 45 cpm and need a residence time of X (from the calculation above) to warm the beer properly?

A: Why don't you consider putting in a beer warmer so beer is instantaneously warmed to 64–68°F? I recall one particular brewery that looked at a "warming tunnel" but didn't like how high the temperature of the water needed to be (125°F) or how difficult it was to control the beer temperature. It seemed that to get the interior core of the beer up to 65–70°F, the beer next to the can wall would get close to the temperature of the water, possibly harming or autolyzing the yeast. Their current beer warmer is programmed so that if the water temperature goes above 77°F, the beer flow stops and the unit goes into recirculation to avoid "cooking" the beer.

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