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Ask the Experts: Chris White & Jamil Zainasheff

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Andrew from Maryland asks:
I used to aerate starters by intermittent shaking and recently moved to a stir plate. My beer ferment profile: using WLP550,WY3711, WY3522-was fairly consistent.(as consistent as Belgian yeasts can be).Since I got the stir plate, I decant and pitch, get lag times of 6-12 hours, and furious ferments lasting 24-36 hours.

The puzzling part is now the yeast stays in suspension for 7-10 days and will suddenly drop like a rock. I have hit low end FGs depending on the beer but not always full attenuation which leaves some residual sweetness. The beer is still good but I would like to know what's causing the yeast to remain in suspension for so long so I can re-jigger my fermentation management. I use the Mr. Malty pitching calculator. My starter wort is around 1.035, and I add yeast nutrient. I have not changed my brewing processes. I brush my teeth and say my prayers.

Thanks for making yourselves available for questions.

Chris and Jamil answer:
There are a couple things to consider. Are you getting lower or higher levels of measured attenuation or does the beer just seem sweeter to you and you are assuming it is not attenuating as much? A number of factors affect sweetness. It might be that the change in fermentation is producing more alcohols that have a sweet character to them. Or it might be that the change in pitch rate is resulting in more yeast surface area and it is pulling more of the hop bittering out of the beer when it settles.

Another consideration is how is your starter process? Often brewers will decant the starter before some of the more attenuative yeast have settled. This makes for a less attenuative fermentation, because you’ve thrown away the yeast that were still working. Sometimes in switching to a stir plate, brewers will leave the starter on there much longer than necessary. Growth is often complete in just a couple days, but they will leave the yeast sitting warm for a week. This ends up depleting the yeast reserves and weakening the yeast.

There are a few things you can try to help resolve this mystery.

First, you should try doing a forced ferment test. This will see what the actual terminal gravity might be for that wort/yeast combination. The second thing you might do is to take a gravity reading each day. We doubt that full attenuation was reached in 24 to 36 hours. If the gravity keeps dropping during the 7 to 10 days, then it is likely either you are not pitching enough yeast or the yeast are deficient in some nutrient or oxygen. You don’t mention the starting gravity of the beers you are making, but if they are high gravity, they may need more yeast, more nutrients, and more oxygen to fully attenuate. Another thing you can try if the previous efforts don’t solve the problem is to try fermenting with a well known, very consistent strain, such as White Labs WLP001. Do everything the same and see if you get the same result. If so, then it is certainly your starter process.

Robert from Washington asks:
I recently brewed a Munich Dunkel. When I started drinking the beer, I noticed a bit a diacetyll in the nose, nothing really in the taste. I used a single decoction from protein rest to saccharification rest. The grist was 10lbs munich light and 6 oz of chocolate. I used Wyeast Bavarian Lager from a local brewery and used a yeast starter. I did not add any yeast nutrient to the wort directly, just a small amount to the starter. I also do not have an aeration or oxygenation system. But, I'm thinking the diacetyl came from a deficiency of free amino nitrogen. Will adding yeast nutrient to the boil and adding more oxygen reduce the diacetyl in the finished beer with still doing a decoction? Is a decoction even necessary or can I achieve the same results with adding some melanoidin malt?

Second, I will be purchasing an oxygenation system. I was wondering how can I achieve the proper level of oxygen of 8-10 ppm? Is there a guideline I can reference or and equation to help calculate the proper levels based upon volume, gravity, etc...?

Thank you

Chris and Jamil answer:
It is important to know all of the aspects of fermentation to truly understand the source of a problem, like excessive diacetyl. Keep in mind that temperatures, pitching rates, yeast health, and yeast purity, all play a large role in diacetyl levels in beer. Without that information it is difficult to declare that the problem was from a nutrient deficiency and/or a lack of oxygen. However, it certainly is something that you should address if you are serious about brewing a quality lager. Chances are good that addressing these issues will have an impact on the amount of diacetyl. One more thing, you mention getting a pitch of yeast from a local brewery. When homebrewers do this, they often get more yeast than needed and over pitch. Over pitching can also cause a higher level of diacetyl in the finished beer, so try to measure the amount of yeast pitched and pitch the proper amount. Longer conditioning time on the yeast, especially at elevated temperature (diacetyl rest), can help reduce diacetyl.

Ben from Illinois asks:
I recently made my first yeast starter for my latest cream ale. I think I had a problem with infection in my Erlenmeyer flask. Before I used it I cleaned it and over cautiously sanitized with Iodophor. I made a small 1.045 wort with Pilsen DME. I then boiled it for 20 minutes, cooled down the flask in an ice bath, and pitched WLP810 San Fran lager yeast at about 68F.This was my fermenting temp. I covered it with tin foil and let it sit for 4 days in my kitchen. It smelled a little like sour wine on brew day. Against my better judgment I pitched it anyway, liquid and all. Although the beer is a young 2 weeks, it still smells sour. My big questions here are,

Should I use a bung and airlock for my starters? Tin foil just seems a little unsanitary and I think I just proved it with my sour cream ale. Did this happen as a characteristic of high temp lager yeast fermentation? Maybe too high? Or is this a characteristic of the young beer that will fade with a lagering period of a couple months?

Chris and Jamil answer:
Covering the flask with foil so that it hangs down about three inches all around should provide plenty of protection unless you have insects crawling around. You don’t want to use a stopper and airlock. It is harder to ensure it is sanitary and it can result in less air exchange for the starter.

We would have to taste the beer or starter to know for certain whether it is a bacterial, wild yeast, or other issue such as high levels of sulfur. The flavor you get from a warmer lager fermentation depends a lot on yeast strain.

Contamination is always a possibility with starters, which is why caution is needed. A good method is to use a Pyrex or Bomex flask and boil directly in the flask with the top covered with the foil. This will sanitize not only the wort, but the flask, and the foil. When it comes time to cool the starter, keep the foil on. When it comes time to add your yeast, work in a draft free area and do not uncover the flask any longer than is necessary.

Dan from New Jersey asks:
I understand that transferring the beer is mostly unnecessary when brewing beers of average gravity. Also from the information I've gathered autolysis is not a major issue at the home brew level if one happens to leave the beer for extended periods on the yeast cake. My method is to try to get a healthy fermentation using proper aeration and pitching rates, allow the beer to ferment out and then give it a few days to "clean up after itself." I will take a hydrometer reading and if the gravity is good and I don't smell or taste any diacetyl I go ahead and keg or bottle the beer. Here is my question. I have read a lot of forum posts where folks say leaving beer in the fermenter for much longer periods will drastically improve the flavor. I am talking anywhere from 3 weeks to 3 months, most of these posts claim it is the yeast "clearing up after itself". What I am wondering is after the yeast drop out and beer tastes ready to bottle or keg is the yeast actually doing anything in these extended time frames? Reading in your Yeast book I see maximums times of 15 hours lag phase, four days growth phase and ten days stationary phase, that comes to around fifteen days total. So if the beer appears ready to bottle or keg after 15 days will leaving on the yeast an extra week or multiple weeks have a major impact on the flavor? Also what exactly is the yeast doing, if anything in this time? I am sure it depends, but I hope you can clarify this a bit for me.

Thanks for your time

Chris and Jamil answer:
Your method is sound and I would question the wisdom of leaving beer on the yeast for much longer than what you outline in your process. Yes, the yeast (if healthy and not in a high alcohol environment) probably won’t cause any off flavors if the storage time is extended, but it really isn’t doing much to help the beer either, unless the beer quality was poor going into it. For example, perhaps someone had a fermentation that was sluggish, full of diacetyl, or other compounds. In that case, maybe it helped to rest on the yeast for a long period of time. However, you are doing the right thing. Ensure proper fermentation from the start with healthy yeast, proper pitching rates, nutrients, and temperature control. Perform a taste test and if there are no problems, package the beer.

Mark from Pennsylvania asks:
I’m enjoying your book on yeast. I have a microbiology background, so it’s been very interesting on a lot of levels. I have a question regarding storage of a yeast slurry under distilled water. Since, the yeast are in hibernation from the de-ionized water, I’ll need to wake them up before pitching. I won’t need a starter because I’ll already have lots of yeast from the slurry. I was thinking of letting the slurry warm to room temperature, decanting the water, adding some low gravity wort, and re-suspending the yeast several hours before pitching to let the cells acclimate themselves to the new environment. Does this sound like a plan?

Thanks in advance.

Chris and Jamil answer:
Yes, that sounds like a reasonable plan, although the level of success you have will depend on several factors such as how long you store the yeast under de-ionized water, at what temperature, the initial yeast health, and the strain. Storage under de-ionized water is still quite stressful for the yeast and viability could be very low depending on storage conditions. If the storage time is brief and cold, then it is less of an issue. The longer the storage time, the warmer the temperature, the more important it is to restore the yeast to health through a starter. If storage was very stressful, it might be necessary to start fresh.


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