[Bel Air Brewing]

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.

[Saccharomyces]

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.

[denny]

There is no eeet number of reuses.  You need to use your experience to know.

[Bel Air Brewing]

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?  Why have to remember that the yeast cultures that we enjoy today are the result of continuous repitching.

Less crisp / dry, and more malt forward. That is my description of the profile.

Another brewing partner just stated..."less clean".

[Bel Air Brewing]

There is no eeet number of reuses.  You need to use your experience to know.

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.

[denny]

There is no eeet number of reuses.  You need to use your experience to know.

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 I 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.

[ynotbrusum]

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...

[dannyjed]

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.


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[Saccharomyces]

We harvest straight from SS conical fermenters into glass jugs with airlocks. And store the yeast at 36-38 F.

What part of the cone?  You need to harvest from the middle of the cake in the cone.

[Saccharomyces]

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...

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.

[Bel Air Brewing]

We harvest straight from SS conical fermenters into glass jugs with airlocks. And store the yeast at 36-38 F.

What part of the cone?  You need to harvest from the middle of cake in the cone.

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.

[Bel Air Brewing]

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.

[erockrph]

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.

[Saccharomyces]

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.

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.

[denny]

We harvest straight from SS conical fermenters into glass jugs with airlocks. And store the yeast at 36-38 F.

What part of the cone?  You need to harvest from the middle of the cake in the cone.

Mark, I think I'd take exception to "need to".  I certainly don't and it hasn't caused any problems.