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Ask the Experts: Chris White & Jamil Zainasheff

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Chris White
Chris White is President of White Labs and Co-Author of Yeast: The Practical Guide to Beer Fermentation.

Chris' interest in homebrewing came from undergraduate studies at UC Davis, when he signed up for Michael Lewis' brewing course. Chris then completed a Ph.D. thesis on yeast biochemistry at UC San Diego. He founded White Labs as a yeast and fermentation laboratory for brewers and homebrewers in 1995. He is active as President of White Labs, and enjoys growing the company worldwide and moving into new areas of fermentation such as distilled products and wine. Chris White is also a faculty member of Siebel Institute of Technology in Chicago. Chris is a member of the American Society for Brewing Chemists and the Master Brewers Association of America. He enjoys traveling, golf, talking beer, and barbeques with friends.

Jamil Zainasheff
Jamil Zainasheff is an award-winning homebrewer, beer judge, author, and host of "The Jamil Show" and "Brew Strong" shows on The Brewing Network. Jamil has brewed an award winning example of every style of beer described in the Beer Judge Certification Program (BJCP) Style Guidelines. He has co-authored two critically acclaimed brewing books, Brewing Classic Styles and Yeast: The Practical Guide to Beer Fermentation. Jamil's newest venture is Heretic Brewing Company, located in Pittsburg, California.

Oscar from Pennsylvania asks:
On a recent visit to Holland, my aunt, who is just learning of my new found homebrewing hobby, told me of a friend of hers who used to be a brewer for Groslch. He told her proudly they got new yeast from Denmark every two weeks. Later on during the visit, a brewer from Brewery Het Ij (pronounce het aye), a micro brewery in Amsterdam, told me they have propagated the same "house" strain for 25 years now. I have also taken note that many of the recipes I read about from American breweries list "proprietary strain" as their yeast used. So which is it? Does the yeast get tired if used over and over again? Or, if you pamper your yeast and get it used to living with you, can you propagate a strain to be your best friend for ever, allowing it to adapt to the conditions in your brewery? I know this may not be what our good friends at White& Wyeast want to hear, but then again, as a home brewer the thought of having a house strain for your "special" beer flavors is intriguing.


Chris and Jamil answer:
You can keep yeast forever, given the right conditions. Of course, for most brewers contamination eventually increases to a point where they want to start with a fresh pitch of yeast.

Yeast do mutate, and those mutations will build up over time, changing the yeast in ways that may or may not be desirable. Much of it depends on the brewer, how you handle the yeast and how you select the yeast to use with the next batch. If you only select the yeast that does well and produces flavors you like, perhaps over time it will change enough that you can consider it your own proprietary strain.

Don asks:
I’m getting back into home brewing and trying to improve my brewing process while still keeping the fuss to what is practical. My research so far has confused me somewhat - the subject is head space in a primary fermenter and considering the practicalities of aerating. Whichever way you choose to aerate, whether by venturi transfer (e.g., via Wort Wizard) or an aquarium pump. As well as taking into consideration that some head space is required for the early boisterous phase of primary fermentation. What volume of initial head space should be considered for a venturi transfer or an adequate amount of pumping air via, for example, an aquarium pump - 20% of volume, 30%? Is this really an issue or am I creating unnecessary concern here?

Advice would be appreciated.

Chris and Jamil answer:
While it is probably possible to calculate the available O2 trapped in the headspace and later dissolved in the wort, it is not worth the trouble. Just make sure you have the right amount of space to allow for fermentation (or hook up a blow off tube). Measure the duration and any other settings that you use to add oxygen. Taste the beer once fermented. Keep notes. The next batch try to increase or decrease the oxygen added and see if your results improve. This is how I did it as a homebrewer. It didn’t matter what the actual number might be. When it tastes great, you have the right amount of O2.

One last thought. We are not fans of venturi devices for oxygenation. It is questionable how much oxygen is dissolved into the wort with these devices. It may be more effective to shake the fermenter. The worst part about venturi machines is that they pull in air and with it dust, which is not sanitary.

Jeffery asks:
1. I recently brewed an English IPA with an OG of 1.065 using WLP002. I made a proper starter, oxygenated from about 1 minute, and fermented at 65ºF rising to 67ºF at the end of fermentation. The beer ended up fairly fruity (cherry and almost a little fruity/tart), which was the opposite of what I was trying to accomplish. The only irregularity was that I over chilled the wort to 58ºF, pitched, and then brought the temp to 65ºF over about 3 hours. Can you offer some tips for reducing fruity esters with English yeasts? How cool could you go for the first couple days?

2. I brew a yearly Belgian Strong Golden that is one of my most successful beers. I use and love WLP570 for it, but It's always a hassle to get it to clear. I usually keg, fine with gelatin and then bottle later. This year the yeast made more sulfur than it has in the past. What factors influence sulfur production in beer yeast? I have been "burping" the kegs for the last couple months and the aroma is greatly reduced but not gone. With wine one must be cautious with H2S because it can form mercaptans and disulfides that are harder to get rid of than H2S. I have used CuSO4 at work for such problems. Is there a risk to allowing beer to have some sulfur for extended periods? Once bottled, it will never go away right?

Chris and Jamil answer:
You want to avoid stressing the yeast, causing them to express heat shock proteins with large temperature changes. It would have been better to change the wort temperature before pitching the yeast.

As for fruitiness, it is a complex question that depends on the pitching rates, oxygen levels, yeast health, nutrients, wort gravity, temperature, etc. Keep in mind that in general low cell counts + heat + oxygen will result in more ester production. Stress will cause yeast to produce more sulfur. Stress comes in many forms, but the most common causes would be temperature changes, high gravity worts, or a lack of certain nutrients. H2S is related to yeast growth, but normally the evolution of CO2 from fermentation will drive the sulfur off. Capping fermentation early or dropping the temperature early can trap more sulfur in the beer. Wort spoilage organisms can also create H2S.

It is important to taste your beer before kegging. If you notice that a flavor needs correcting, it is often easier to keep it in the fermenter and let the yeast help by raising the temp a little. H2S is quite volatile and mostly blows off, while SO2 can combine with aldehydes, forming compounds that persist.

Allen from New York asks:
I have some top cropping yeast questions. I have found an ”english" origin yeast that is a great top cropper and has a flavor profile I like. In your yeast book, you mention not using the "first skim" as it has proteins and such. My question; are you supposed to completely skim all yeast off the surface and discard it, then collect subsequent skims? I have been top cropping for over a year now, and I have just used the first skim because I am worried that discarding all the yeast from the surface of the beer will screw up the fermentation. Is discarding all the krausen i.e. first skim the proper method, or will it "stunt" the fermentation?

You also say in your book that using a wet weight of slurry is a decent way to measure the yeast slurry from batch to batch. As a top cropper, I have tried to be "consistent" with the amount of top cropped yeast (measured in grams) from batch to batch, but I have no idea if I am pitching the proper amount of cells. Is there any way to come up with a "weight range" of top cropped slurry for re-pitching (assuming the beer is brewed within two weeks with optimal storage)?

When top cropping, I try to "select" yeast about the same number of hours after the initial pitch for consistency. That is 48 hours for me. Depending on what the answer for the first question above, if I am to discard the first skim, when should I do the first skim (48 hours after pitch)? How long will it take to get a second skim (minutes or hours away)? I know the timing could be different by strain, but let us assume the yeast is great top cropper and not one that has to be trained to top crop.

Thanks in advance for your answers, and I loved the yeast book.

Chris and Jamil answer:
You just need to scrape off the very top of the yeast layer and that will get rid of most of the non-yeast material. If you want the purest yeast, the second crop after removing the first should be cleaner. However, not all strains will produce a second crop. If the strain you are working with produces another crop, then there is little need to worry. You might try pitching the same wort with yeast from the first crop and from the second crop. You might get a slightly different ferment from one versus the other. One might be slightly more attenuative or produce a different flavor, so try both ways.

As far as weight, the old British rule of 1 lb of yeast per British barrel might be something you could use. Those brewers were often top cropping, so the number might work well for you.

Your timing sounds good. 48 hours is about right, depending on the yeast and conditions. If you are discarding the first crop then take care of that somewhere between 24 to 36 hours.


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