I have read that the max number of yeast generations to use is around 6, or maybe 8.
How do you know when to discard the yeast and start with a new fresh batch?
Bel Air Brewing kegged up 20 gallons of Fest Bier. The yeast was W-34/70, perhaps the 9th generation. We noticed that it was not as clean tasting as it was previously. Is this a sign that it’s time to dump it?
I know some of you state that there is no limit on this. But the most gens that we have used in the past is about 6.
How would you describe “not as clean tasting?” All yeast strains mutate over time. How do you crop? Are you placing stress on the culture? We have to remember that the yeast cultures that we enjoy today are the result of continuous repitching.
There is no eeet number of reuses. You need to use your experience to know.
Less crisp / dry, and more malt forward. That is my description of the profile.
Another brewing partner just stated…“less clean”.
Our experience is re-pitching 6, maybe 7 times. Never gone over that in years past. Just wondering how far can you go without the yeast mutating into some off flavored, undesirable yeast.
We harvest straight from SS conical fermenters into glass jugs with airlocks. And store the yeast at 36-38 F.
It depends so much on your harvest and storage processes that’s it’s impossible to say.
I recently went 5 uses in an Alt yeast and by the last one, I caught some phenolics. I assume a wild yeast. This time of year there is a lot of micro flora in the air, so despite meticulous sanitation, those airborne critters can get in there…
If you’re worried, just add new packages of W 34/70. It’s cheap enough and after another 5 uses it more than pays for itself.
What part of the cone? You need to harvest from the middle of the cake in the cone.
I have been in Alan Pugsley-built breweries that have been repitching the same culture for twenty years or more and they skim yeast from the top where the culture is susceptible to wild yeast infection. My bet is on selective pressure being placed on the culture. I have learned more about yeast by keeping a sourdough culture than I ever learned about yeast by keeping pure cultures. A sourdough culture is a potpourri of yeast strains and bacteria. It is a great teaching tool because one can see how cropping practice and propagation technique can affect a culture by pushing it one way or another. The average yeast crop contains between 40 and 60% yeast solids and can be assumed to contain 1.2B viable yeast cells per ml; therefore, approximately 167ml of yeast solids contains approximately 200B viable yeast cells. That is a pitching rate of 10m cells per milliliter in a 5-gallon batch. If pitching 10 gallons, increase the amount of slurry to 334ml. There is absolutely no way that a wild yeast strain that was not introduced on the initial pitch can compete with that volume of domesticated yeast. The only way that a wild yeast can impact a domestic culture is if it was originally pitched with the culture because every repitch is an opportunity for the wild yeast strain to replicate. After about four or five repitches, nothing stands a chance of competing with the yeast culture that is pitched because it has acclimated to one’s brewery.
If you do not believe me, take the steps necessary to grow a sourdough culture using only unbleached whole wheat flour and water (unbleached rye flour has a higher microflora content, but whole wheat is easier to obtain). After the starter reaches the point where it will double in volume, pitch 1/2 gram of active dry yeast into 400 grams of sourdough starter. Within three to four feeding cycles, the active dry yeast will dominate the culture. I have one such culture that I refer to as Natasha. There is slight wild note to this culture when making bread, but it never becomes sweetart sour because the domesticated yeast keeps lactobacillus and acetobacter in check. I have another culture that is pure wild microflora that I call Boris. This culture can become sweetart sour if the fermentation is retarded more than 24 hours. I use Natasha for my pizza and calazone dough ferments. Boris is used for straight-up artisan sourdough baking.
Ok…we have always used the entire slurry / yeast cake in the cone. It is nearly impossible to discriminate between the middle, top or bottom of the cake. It’s evenly distributed on the sides of the cone.
The fragrance is always clean, and fresh.
Of the 30 gallons of Fest Bier, Wyeast Oktoberfest Blend was used for 20 gallons, fresh brand new smack-packs. The W-34/70 (6th gen) was used for 10 gallons after I read that it makes a fine Fest Bier. Maybe so, but three of the Bel Air Brewing partners preferred the Wyeast 2633.
I do too. 34/70 makes great lagers, and is practically bulletproof, but when I compare lagers I’ve brewed with 34/70 vs other lager yeasts I frequently use (S-189, 2633, 2278) the 34/70 beers are missing something. I’m not sure if it’s missing a hint of sulfur, or if it is scalping some of the noble hop flavor, or some combination of the two. It’s subtle, and I really only notice it if I’ve been drinking a batch made with 34/70 for a while, then tap one brewed with a different lager yeast.
I am assuming that you do not have a valve part of the way up the cone from which to harvest yeast. If you do not have a harvesting valve and the conical is not too tall, you can crop from the top of cone. You have to determine the volume of the yeast cake. Here is the formula for the volume of a cone:
volume = 3.14 * radius^2 * (height / 3), where the symbol “^” denotes raised to the power of
The radius here is the diameter at that top of the cake divided by 2 because the cone is inverted. Let’s say the diameter of the cone at the top of the cake is 4" and the height cake is 4".
radius = diameter / 2
volume = 3.14 * 2^2 * (4 / 3) = 3.14 * 4 * 1.33 = 16.7 cubic inches
The formula for cubic inches to milliliters conversion is: mL = cubic inches / 0.061024 = ~274 ml
We could divide the cake into thirds, but that is not how yeast settles out of suspension. If you have ever used a carboy, then you know that about a fifth of the sediment is break and particulate matter. We can assume that the next fifth or so is early flocculating and dead yeast cells. That leaves us with three fifths of the contents left to crop. However, the topmost layer consists of cells that have lost or losing their ability to flocculate. We do not want these yeast cells. A wise thing to do is to carefully remove and discard the top-most one fifth of the of the sediment. In this case, we want to skim 274 / 5 = 55ml from the top of the cone. We can then take our crop from the next two fifths, which is 110ml. The last two fifths is discarded. This cropping technique is far from perfect, but it should yield the best cells. One does not want to repitch the dead and early flocculating cells or the break. Because if you are repitching everything, the percentage of dead cells will increase with every repitch. Avoiding repitching the late flocculating yeast cells will should keep the culture from getting “powdery.”
By the way, if you take your cone height and radius measurements in centimeters and use the volume of a cone formula to calculate cubic centimeters, one cubic centimeter (CC) equals one milliliter. That is why you see some syringes with CC instead mL markings.
Mark, I think I’d take exception to “need to”. I certainly don’t and it hasn’t caused any problems.
The OP appears to want to repitch more than a handful of times. However, he appears to be serially repitching the entire cone. In order to do that without degradation of performance and flavor, one cannot continue to repitch dead as well as early and late floccing cells. That is why pro brewers crop from the middle of the cone. It is the conical equivalent taking the middle head from a true top-cropper. Can one pitch the entire contents? Absolutely, but not without paying a price when serially repitching.
I guess what I’m saying is that maybe you shou,d try to qualify your answers a bit. Believe me, I learned the hard way about making overly broad statements. While I have no reason to doubt your advice on this I also know that other methods work also.
I get it, Denny. I have repitched the entire contents minus the break and dead cells, which is pretty easy to accomplish in a 5-gallon-size batch by leaving behind about a pint of green beer, swirling the culture into suspension, and waiting a few minutes for the break and dead cells to sediment out before decanting the cells that are still in suspension. That works for a few repitches, but ultimately culture degrades over time. I serially repitched a true top-cropping yeast strain that I acquired from the NCYC in England a dozen times without a degradation in performance. That is when the practice of discarding the brown head and cropping the second head became crystal clear. This particular culture was not the easiest to use due to being a Yorkshire culture and Yorkshire cultures are notorious for having high O2 requirements. If a brewer is not careful, Yorkshire cultures can come out of suspension early and leave a brewer with a diacetyl bomb.
Here is the brown head forming from that culture:
Here is the second head that formed after the brown head was skimmed:
I could repitch the second head indefinitely without a degradation in performance. Sure, the culture would adopt a house character from selective pressure, but it would not become powdery or start to develop off-tastes due to an ever increasing dead cell count. That is what happens when a brewer who serially repitches does not select from the middle of the cone. In the end, does a brewer have to select the cells from the middle of the cone? Well, not if he/she only plans to repitch the culture a handful of times before returning to the reference culture. However, for those who want to repitch a culture until it adapts to their brewery, selecting from the middle of the cake is not an option, nor is plating the middle of the cake after a number of repitches. The goal is to select cells that perform well in one’s brewery.
Here are a couple pics of the harvested W-34/70, 7th generation. There is over 1/2 gallon, probably almost 3 qts. The aroma is very clean, and fresh. No “off” odors at all.
[quote=“Saccharomyces, post:10, topic:30294, username:Saccharomyces”]
Can someone say “Moose and Squirrel”? Sorry, bad humor here. Couldn’t help myself!
That said, good information here, Mark! Thanks!
