Yeast Cultures. How long have you kept your culture alive?

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Yeast Cultures. How long have you kept your culture alive?

Postby stumpwater » Thu Apr 25, 2002 2:36 pm

I checked this sites search database and came up a little dry on the subject of repitching or reusing yeast. Although an old thread did provide a little help, I still have a few questions about reusing my yeast culture.

Does anyone know where to get really good information on yeast and how it carries out the process of fermentation? How the heck does a Belgian Abbey keep a strain alive for 400 years, or the Cooper beer company keep their strain alive for 100+ years? Anyone know the answers? I would be happy to learn of someone who has kept a yeast culture going (on the homebrew level) for anything over 6 months. Post your results. Tell me what kind of culture it is and how long you have used it. Please include how you did this if you would. I really want to know how to keep cultures alive for future use.
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Mesa.... you da man.

Postby Sven » Fri Apr 26, 2002 12:36 am

Mesa,
Thank you for the wealth of knowledge. I have been contemplating yeast culturing for some time now, but I still have quite a few other purchases to finish off my home-brewery before I take that step. Right now I am currently growing my own hops and I hope to have a yeild this fall that is sufficient enough to brew a couple of batches. After I see how I faire at hop growing I was planning on progressing to yeast culturing. So I will have a lot of questions for you some time this winter.
Thanks again for all of your helpful posts.
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Whether pro or otherwise... yeast management is the same....

Postby Mesa Maltworks » Fri Apr 26, 2002 8:17 am

Great questions...long and involved answers though !

The way that brewers keep their yeast in proper form is the same whether you are a home brewer or a pro brewer. The question becomes... do you need to do yeast management because you have a strain that is hard to come by or do you want to reduce pitching cost? If cost is the concern, you have to consider the equipment and time involved when weighing cost advantages. Then there is the possibility that improper technique or lack of post-culture management may lead to improper performance or worse, infection. If you use commercially available strains from White Labs, Wyeast, Brewtec, etc... they are so cheap to simply re-buy and require significantly less fuss that for most home brewers, culturing is not worth it.

Now... if you enjoy the process and experimentation, that is a different story.

There is a GREAT book available that describes IN ENGLISH how to culture yeast on a homebrew scale by Pierre Rajotte or there is a more pamphlet like book by Rog Leistad called Yeast Culturing for the Homebrewer. The latter is really just a book that tells you how to snag yeast from bottles, plate them out, grab a single colony and propagate it to pitching volume and does not deal with storage or assessment. The first book, however, gets into yeast assessment and cell counting which, if you are serious about the topic, is required. The reason it is required to know cell counts is to ensure you are supplying the right amount of yeast for a healty fermentation (neither too high or too low) and the assessment methods to determine the amount of viable vs. dead cells so that you can correct the pitching amount to take that into account. The remaining assessment techniques are required so that you can pre-determine whether there are problems PRIOR to brewing, thereby avoiding bad batches. All of these techniques require a high powered microscope, a hemocytometer (counting cell) and viability stains in addition to culture tubes, agar medias, pyrex plates and other supportive equipment. For cultures to last the maximum amount of time, you also need a refrigerator that will not share any food products with the stored plates (mold & bacteria risk otherwise) and be kept at about 35 degrees.

The practice of yeast management is not hard, it just requires strict attention to detail and some special equipment.

Also... you are dealing with techniques that have to be done maintaining ABSOLUTE sterility. You need to evaluate whether you can maintain these conditions at all times prior to starting.

Now to address some of your other questions....

1) How commercial breweries keep their strains alive:

- The have great laboratories ! They monitor every fermentation in a very scientific manner (even the traditional ones!) and constantly assess their strains for bacteria and wild yeast contamination as well as viability. Commercial brewers also have the advantage of continuous fermentation helping them out, unlike homebrewers. They work out their brewing schedule so that when 1 batch is done fermenting, another batch of fresh wort is placed on top of the yeast immediately after transfer. The forum user "fraoch" has many times posted topics regarding open fermentation at commercial breweries... this practice, combined with skimming is how they keep the "meanies" at bay... but the also have great labs and perform the same quality control as any other brewer.

2) How to keep strains in extended storage in a home brew setting.

- Actually to do this, you snag about 1 million or so cells from the SECONDARY fermenter, plate them on agar media, let them grow, pick a small, healthy colony, propagate it in a test tube until all the sugar ferments out and the yeast flocculates (settles). Then you pour the supernate (the liquid) off the top and replace it with pre-sterilized distilled water and refrigerate it. Yeast prepared in this way will last 8~12 months with no intervention. Anything longer than this is beyond homebrewers. The worst thing you can do is try to store yeast with beer on top of it for more than 2 weeks. Now that I've said this, I know someone will chime in and say they have done this successfully. I agree, I did it to when I thought I was "culturing" as a homebrewer. The reason most people don't find out this is a problematic practice is because they rarely brew the exact same beer back to back and have no basis for comparison. This practice is VERY stressful on the yeast because alcohol is toxic to them and quickly results in cell death. This problem is compounded because the osmotic pressure is greater on the outside walls of the cell than the inside which causes them to rupture causing even more cell death ! It is primarily for these two reasons the supernate on top should be distilled water, NOT beer. Also... yeast in cold stasis need NO sugars, just glycogen which serves as their energy source during dormancy. Lack of attention to these matters lead to inconsistent results, frustration and worst, lost batches !

3) Strains...

Most strains do quite well with the techniques I have outline, but I have had difficulty with a couple both at home and in my breweries lab. The really phenolic, estery varieties of Weitzen strains are very difficult to maintain properly because they seem to have some sort of metabolic weakness. Even with all of the crap I use to monitor my fermentations, assessing this problem is beyond the scope of what I can do to change this. To really answer the cause of the problem here would require biochemical trace testing that would require $40,000 + equipment. So... I simply keep this one going for the required number of batches (I usually produce 2,040 gallons in a brew cycle on this beer) and then dump it. When I want to brew again, I order a fresh propagate from my yeast supplier. There are a couple of other strains that are hard to manage, but luckily they are the exceptions. Otherwise, after the 6th re-pich or so, I grab 1 million cells from the cone of my conical fermenter and re-culture it just like I mentioned above. When the time comes, I get the culture out of the fridge, propagate it progressively up to volume (usually around 14~17 gallons of slurry, but is actually done by cell count, not volume)and pitch it into a new batch. This is EXACTLY the same technique as a homebrewer should use, just much less volume.

In summary... don't let me scare you off from this, just do alot of reading prior to deciding if this is something you wish to do. I would be happy to help anyone in getting going that is interested, simply ask !

Just as an aside.... prior to merging with Ohio Brewing Company, I owned & operated Mesa Maltworks Brewing and Microbiological (ever wonder where my screen name came from?) for 4 years during which yeast management was my primary line of business. My site is still up if you are interested in seeing what we did and other tidbits: www.mesamaltworks.com .

I hope this helped...

Eric
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