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Master Brewers Association of the Americas > BREWING RESOURCES > Ask the Brewmaster
August 18
Calibrating DO meters

Q: ​How important is the BBT ppb readings on the D.O. sensors? I have been using 99.999% nitrogen which was given to me by Hamilton to zero the sensors. When I look at the specs of the gas, it says that it can have < than 2ppm o2. I am not sure that is good enough if we are trying to zero and read ppb? Even the 99.9999% can still have .5ppm O2? I have a hard time understanding the correlation of O2 in nitrogen (ppm) and O2 in beer (ppb). Is there a calculation I can use to prove this out? Also the “0” calibration and the span “210000ppm 0r 21% O2”  seems like a huge span to then try and read accurately in the ppb range. If I could find it, I would love to get a “standard” D.O in solution of 25ppb to verify calibration.

A: Extremely important - decreasing DO in the BBT is absolutely necessary to produce the best possible beer. Most DO meters for this application are accurate to about +/-1 ppb.

For both gas phase and liquid phase (DO), the O2 content can be expressed in the unit ppm (which is very confusing). However, the unit for gas is ppm vol/vol and the unit for liquid (DO) ppm m/m, so these are completely different units. As rule of the thumb, the conversion of ppm vol/vol and ppm m/m is 20,000:1

Taking your specification of the class 5.0 nitrogen with a purity of 99.999% which still can have < 2ppm O2. These are 2 ppm vol/vol and equals 2/20,000 is 0,0001 ppm m/m = 0,1 ppb m/m DO. This gas is perfectly suited for performing a zero point calibration/verification. There are procedures for creating "liquid zero" standards, but this is less accurate than using the gas standard that you already have.

It may be challenging to create or purchase a 25ppb liquid standard. An option could be requesting a certified (or even better) accredited gas mixture of N2 with an O2 content of 50 ppm vol/vol which equals approx. 25ppb m/m DO (check its availability). During the O2 verification it's important that the gas and O2 meter have a very similar temperature and the gas flow is low, so you do not have pressure build up in the O2 meter.

If you want a more practical, lo-tech opton, many breweries keep an aged beer standard of known DO in house to use as a quick, rough calibration check.

Many thanks to Frank Verkoelen and Jeff Tocio (Pentair Haffmans), as well as Kevin Sudderth (Hach) for their invaluable contributions to this response.

August 10
Removing Fine DE

​Q: Brewmaster,

My Operations Manager has decided to remove the fine Kieselguhr from our filtration pre-coat and body feeds and replace it with coarse Kieselguhr as a cost saving measure. Prior to this decision we were using approximately a 2:1 ratio of coarse kieselguhr to fine in the pre-coats and body feeds. Is there a significant difference in effectiveness of filtration of fine vs coarse kieselguhr? Could removing of the fine kieselguhr cause filtration problems? Additional info: We use a frame type filter press. We currently do two pre-coats consisting of  a mixture of coarse and fine kieselguhr. and 4 body feeds for approximately 100 hl of beer

A: In regards to the effectiveness of your filtration, eliminating the fine DE will result in a coarser filtration. Yes, this may be a significant difference. Look at your spent cake and compare it to what came out of the beer previously during the finer filtrations. Whether allowing more particles to pass through your filter into the finished beer is acceptable can only be determined by the load of your unfiltered beer (what and how much of it needs to come out) and your product specifications (desired level of clarity/acceptable haze, colloidal stability, shelf life, etc.) for that given brand. There's no one-size-fits-all answer since there are so many different types of beer on the market and strategies for producing them.

Could removal of the fine DE cause filtration problems? To answer this question I reached out to MBAA member Tom Thilert, who has many years of experience in filtration. Here's a summary of what Tom mentioned:

Since you are using a plate and frame filter, you most likely have (non-active) filter sheets between the frames. Non-active filter sheets contain no DE (they are mostly made of cellulose) and only serve the purpose of supporting the cake. Removing the fine DE might cause blinding of the filter sheet if there are a lot of fines to remove. Otherwise, this should be no problem.

If after removing the fine DE, the sheets don't plug, you have no issue with releasing the cake from the sheets, and the filtered beer meets your product specifications, then there is no problem with removing the fine DE. With no fine DE, you can get away with a single precoat and use the same DE for the entire run. 

Please note: If you are using active sheets for an extra polish filtration, then it is very likely these will plug without the fine DE.

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:

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