[Bel Air Brewing]

I typically will pitch one qt of thick yeast slurry into a 10 gallon batch. Or, a pint per 5 gallons.

This is always the harvested yeast from a previous brew. How many cells are present?

Is this over pitching, and if so, by how much?

[ynotbrusum]

Earlier this year or late last year, I went to a slurry repitch using a stainless ladle - it happened to be just shy of 200 ml.  My results with one ladle or a ladle and a bit more have been good.  I just got lucky, I guess, that I stumbled upon a reasonable re-pitch rate for 5 gallons.  I use shy of 3 ladles for 10 gallon batch re-pitches.  Just my one data point, I know.

[Wilbur]

Omega Yeast did a seminar for my homebrew club recently. Mark highlighted an experiment they did where they scraped a plate and used that to prop a 100 mL starter. They did this with 4 strains, a hefe, lager, kveik, and west coast ale (I believe, I'd have to check my notes). They let it ferment out completely and performed cell counts, which ranged from ~100-900m/mL. The volume was also visually different. They used filter paper to separate the solid from the liquid, and all had the same mass (approximately). Their conclusion was that cell count wasn't a good measure as cell size and other factors came into play. They also mentioned some issues with different yeasts reacting and metabolizing dyes different, which can lead to viability% not matching practical results. Yeast is weird.


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[Cliffs]

Omega Yeast did a seminar for my homebrew club recently. Mark highlighted an experiment they did where they scraped a plate and used that to prop a 100 mL starter. They did this with 4 strains, a hefe, lager, kveik, and west coast ale (I believe, I'd have to check my notes). They let it ferment out completely and performed cell counts, which ranged from ~100-900m/mL. The volume was also visually different. They used filter paper to separate the solid from the liquid, and all had the same mass (approximately). Their conclusion was that cell count wasn't a good measure as cell size and other factors came into play. They also mentioned some issues with different yeasts reacting and metabolizing dyes different, which can lead to viability% not matching practical results. Yeast is weird.


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I think I remember someone saying, you're trading carbon for biomass when it comes to building yeast. So it stands to reason that there would be this much variance.

[Saccharomyces]

I typically will pitch one qt of thick yeast slurry into a 10 gallon batch. Or, a pint per 5 gallons.

This is always the harvested yeast from a previous brew. How many cells are present?

Is this over pitching, and if so, by how much?

A pint is 473ml.   If you are pitching 473ml per 5-gallons, you are overpitching by 473 / 167 = 2.8 times.  That is a significant overpitch.  When the Siebel Institute was in the game of propagating their cultures for microbreweries, their suggested pitch rate was one quart of slurry per barrel.  A barrel is 3.1 times the volume into which you are pitching a quart of slurry.  Unless you guys are total pigs with respect to brewery hygiene, there is nothing to be gained by pitching that much yeast.

[Bel Air Brewing]

I typically will pitch one qt of thick yeast slurry into a 10 gallon batch. Or, a pint per 5 gallons.

This is always the harvested yeast from a previous brew. How many cells are present?

Is this over pitching, and if so, by how much?

A pint is 473ml.   If you are pitching 473ml per 5-gallons, you are overpitching by 473 / 167 = 2.8 times.  That is a significant overpitch.  When the Siebel Institute was in the game of propagating their cultures for microbreweries, their suggested pitch rate was one quart of slurry per barrel.  A barrel is 3.1 times the volume into which you are pitching a quart of slurry.  Unless you guys are total pigs with respect to brewery hygiene, there is nothing to be gained by pitching that much yeast.

Been over pitching for decades. Are we pigs? Oink, Oink! But our pig pen is clean. I spent a lot of time on the farm in Iowa.

[tommymorris]

The thing I have learned from Mark V’s comments lately is you can get away with over pitching for a few repitches of the same yeast, but if you want to keep the same yeast going serially for many batches it is best to not over pitch. 

I am currently hoping to keep some 1450 and a slurry of Mexican lager yeast going for at least 6-10 batches each. I plan to follow Mark’s guidance about doing a 250 ml starter to revive the yeast every few batches. That makes sure I get some cell growth and don’t keep using the same old cells over and over.

[BeerfanOz]

The thing I have learned from Mark V’s comments lately is you can get away with over pitching for a few repitches of the same yeast, but if you want to keep the same yeast going serially for many batches it is best to not over pitch. 

I am currently hoping to keep some 1450 and a slurry of Mexican lager yeast going for at least 6-10 batches each. I plan to follow Mark’s guidance about doing a 250 ml starter to revive the yeast every few batches. That makes sure I get some cell growth and don’t keep using the same old cells over and over.

So if you were going to make a starter from slurry, say, less than 3 months old, how much slurry would you use to how big a starter?.

I generally split the very first gen starter into 3 or 4 small samples, and this gives me up to 6-8 beers easily. But a few times I’ve made a starter from old slurry ( less than 6 months ) and just used maybe half a cup to 2 litres. It’s worked fine when I’ve done it but just wondering how much should I use?

[Saccharomyces]

The thing I have learned from Mark V’s comments lately is you can get away with over pitching for a few repitches of the same yeast, but if you want to keep the same yeast going serially for many batches it is best to not over pitch. 

Hopefully, that is the message people are taking away from this discussion.  Much if what I have written does not apply to the brewer who repitches a culture a couple of times before discarding it.  However, for the brewer who repitches a culture more than two or three times and the brewer who is looking to develop his/her own house yeast culture by serially repitching a culture until it adapts, it is best not to overpitch.

I am currently hoping to keep some 1450 and a slurry of Mexican lager yeast going for at least 6-10 batches each. I plan to follow Mark’s guidance about doing a 250 ml starter to revive the yeast every few batches. That makes sure I get some cell growth and don’t keep using the same old cells over and over.

If you are looking to separate viable cells from dead cells, I have found that decanting only the liquid fraction of the 250ml starter when stepping it up to 1L will produce a relatively clean new culture devoid of dead and weak cells because only the cells that are in suspension get propagated.  If one is short for time and a crop is older than a month or two, one can inoculate a 1L starter with 40ml of thick slurry and only pitch the liquid portion of the starter when inoculating the wort.  The beauty of using a starter with slurry is that it allows one to separate viable yeast from break and dead cells by pitching only the liquid fraction of the starter at high krausen.  The thing about yeast cultures is that they develop variants over time when serially repitching. One can place selective pressure on a culture to control which variants get propagated.  For example, BRY-97 is an isolate of BRY-96 that was acquired from a brewery using BRY-96.  The selective pressure placed on the culture at the brewery resulted in improved flocculation by favoring a variant with better flocculation characteristics.

[Bel Air Brewing]

I decanted about two pints of beer off my harvested W-34/70, then added one quart of fresh wort. Shook it up to get it aerated, and it appeared to be coming back to life. The color went from off gray back to it's light peanut-butter like color. The aroma was nice and clean, so it was pitched into a 10 gallon batch of Munich Helles. 1 pint per 5 gallons.