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Master Brewers Association of the Americas > BREWING RESOURCES > Ask the Brewmaster
July 28
Batch Carbonation

​Q: Dear Brewmaster, 

I work at a brewery on a Caribbean Island, we are having problems with dialing in our CO2 levels in the bright beer tanks. We usually end up with about 100-95HL in our bright beer tank. Coming out of our fermenter our beers usually have 3.5-4.5 grams per liter of CO2. We filter one day then package the next (about a 12-16 hours between end of filtration and beginning of packaging). We generally leave our beers under 1-2 bars of pressure depending on the volume in the tank and time until packaging. On the day of packaging, if our CO2 levels are low we pump more CO2 in from the bottom of the tank. If we are high, we have to release all the pressure from the tank and purge CO2 out of the beer then re-pressurize the tank. (This is very costly for us, and a waste of CO2).

Are there any formulas we can be using that factor in Time, Temp., volume and initial CO2 levels to help us hit our carbonation range in bright beer tank?

Thank you for your insight!

A: Typically, these questions are answered electronically; however, due to your location I think we should consider a site visit to fully assess your situation. 

It sounds like your filtered beer has fairly typical CO2 levels (~1.8-2.3 volumes) compared to what I've seen in the average US microbrewery. You didn't mention your target CO2 spec for packaging, but it's got to be at least a bit higher than the upper end of the range you gave for your filtered beer. Unless your carbonation stone is undersized (or soiled) or cooling is inadequate, hitting your packaging spec in 12-16 hours, without wasting CO2 during the process should be no problem.

First, it's critical to understand that the volume of CO2 dissolved in your beer at any given moment is always equibilrating toward a theoretical value determined by the conditions (temperature and pressure) at that moment. For example, if you were able to maintain 12psi of CO2 head pressure and 35F in your BBT, you'd eventually end up with the 2.73 volumes listed on the charts that come with CO2 volume meters. This would be true regardless of the starting carbonation value; however, it might take days or even weeks to reach 2.73 volumes, depending on your starting value. Since none of us have that kind of time, we use carbonation stones and attempt to optimize temperature and pressure to hit carbonation specs faster. Take note from the chart that, given enough time, beer left under 1-2 bar at cold temperatures will become substantially over-carbonated.

As soon as filtration is complete, record all of the usual suspects: volumes of CO2, beer temp, bbl/hl of beer, tank head pressure, DO, and verify cooling is on the BBT. I'll assume your BBT head pressure at the end of filtration is ~1 bar. If it's low, plug the current temperature and CO2 volumes into your chart to solve for pressure. You'll want to immediately top up head pressure to at least this value to prevent degassing (ie if you have 36F beer and 2.20 volumes CO2, get the head pressure to at least ~7psi). If you will be intentionally venting the tank (to scrub DO) at the beginning of carbonation, be sure head pressure never falls below this point.

To get flow through a carbonation stone, you'll need to set the regulator pressure higher than your desired equilibrium pressure on the chart because you have to overcome hydrostatic pressure (depends on the height of the column of beer in your BBT) and capilary pressure of your porous carbonation stone (depends on the stone, but usually ~5psi). Avoid the temptation to just set the pressure high and let it rip. CO2 injection must be slow to create small bubbles that are readily dissolved. If you go fast, many of the large bubbles created won't dissolve. This results in foaming (which damages foam positive proteins), unnecessary scrubbing (loss of hop aroma/desired volatiles), and a huge waste of CO2. There are 2 common approaches to limiting CO2 flow at higher regulator pressure settings: either step up regulator pressure in small increments over several hours or install a needle valve of some kind (better). Some brewers also use an adjustable PRV on the blow off arm of the BBT so they can set it to blow off at a desired equilibrium pressure. This helps to prevent both over-carbonation (by limiting the max head pressure) and degassing (by limiting venting/the min head pressure). Blow off valves simply left cracked open for venting can cause the head pressure to fall too low - which results in degassing instead of carbonation. Our friends at the Brewers Association put together a very good lecture about carbonation a while back - you might want to check that out for some additional information.
July 22
Process Loss in the Brew Kettle

Q: We are experiencing loss of product throughout the brewing and cellaring processes, one area of loss that we would like to attack is at the kettle.  There is still wort left behind in the trub post boil, even more in our heavily hopped beers.  What are the best ways of increasing our kettle to fermenter volume?  I know of decanters and centrifuges, they are cost prohibitive at this point in our growth.

A: The first step in fighting process loss is to take accurate measurements. Several companies supply sanitary magnetic flow meters, which can be configured for portable use to maximize versatility. These can be used throughout the processes to help identify problems and measure results as you make process adjustments.

A portable mag meter can help you identify serious offenders (which may surprise you) and quantify your results when dealing with obvious, low hanging fruit. A $4,000 mag meter pays for itself pretty quickly if it leads to increased finished beer yields - even if the increases aren’t huge.

Since you’ve identified the brew kettle as a problem area, let’s look at some strategies for decreasing losses there. Typically, there are two major areas of opportunity, and you’ll definitely want to go after both to maximize results:

Create & maintain the perfect trub pile

If you’re able to form (and maintain) a tighter trub pile, you'll get a better yield. There are several variables that can often be controlled with little-to-no equipment modification. These include particle size, wort inlet speed, and wort draw-off speed.

Particle size can be attacked (increased) from several angles, including reducing shear forces and countless upstream process variables. There are also process aids available that can be used to increase trub pile compaction. For example, some kettle fining products incorporate PVPP into the standard blend of carrageenan to form larger flocs. Since the window of optimal whirlpool conditions is limited, it's important to speed up settling by increasing particle size. The bigger the floc, the harder it falls.

If wort is drawn off faster than it can drain from the trub pile, your perfectly formed trub pile will collapse into a soupy mess, resulting in avoidable losses. Additionally, each whirlpool vessel will have its own optimal wort inlet speed. Read this TQ article to understand the mechanics at play.

Reduce the volume of trub 

If the obvious possibility of decreasing your hop additions isn’t on the table, consider shifting some or all of your additions to other products and/or techniques. Hop extracts, hop oils, T-45 pellets, etc. can all increase yield vs. whole leaf or standard T-90 pellets. Hop brokers can sometimes offer a customized solution - they are used to dealing with this issue, so don’t be afraid to ask for help. 

Other Resources

Some other relevant resources authored by MBAA's network of volunteer members are listed below. By the way, other brewers would love to hear about your trials, so please consider summarizing your project to reduce kettle losses in your brewery (and any other interesting projects) in a Technical Quarterly article and/or at a District meeting. Volunteerism is what created the MBAA knowledge base.

  1. TQ: Maximizing Whirlpool Operation (Mallet)    
  2. Poster: The mechanical principles of the whirlpool (Funk)
  3. TQ: The story of the whirlpool (Hudston)
  4. TQ: A new method for trub separation (Versteegh)
  5. TQ: Wort recovery from trub with a decanter centrifuge (Ruggles and Hertrich)
  6. TQ: Control of brewing processing losses (Lieberman)
  7. TQ: Beer recovery - its justifications (hoggan, Ricketts, Spillane)
  8. TQ: Extract control and volume shrinkage in brewing (Schwaiger, Lingelbach, Swistowicz, Fischbach)
  9. TQ: Material and beer losses - their significance, cause, and control (Barnes)
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!
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