Overpitching

I've heard it's difficult to overpitch on a homebrew scale. Does anyone know the actual threshold for overpitching? Is there any quantitative rule-of-thumb? I use Mr Malty, but would like to know what the "safe range" is. Thanks

Because of a poor estimation of a slurry cell count I recently over pitched a Sasion by a factor of about 10 and it didn't have quite as much character as I wanted, but it was present. Generally I think you're better of over pitching.

From WYeast:
http://www.wyeastlab.com/com-pitch-rates.cfm

Info on Mr. Malty and the slurry estimator:
http://woodlandbrew.blogspot.com/2012/11/counting-cells.html

I'd guess it's easy to over pitch homebrew, hard on a commercial scale.

In my inexperienced days, I put a barleywine wort onto an entire belgian yeast cake purely because I saw the strain had a high alcohol tolerance (I was not going for belgian-style flavors). Well the final beer did NOT have any belgian esters and such - it was a fairly clean ferment.

That seems to be the consistent findings around here - if you overpitch, you're losing out on flavor.

And as a final warning against it, I feel that in every aspect we homebrewers should attempt to mimic the procedures of big breweries. They deliberately pitch a certain amount of yeast, and so should we.

Pitching on the yeast cake would be about a huge factor over the recommended. I have about 3-5 trillion cells in the slurry after a 3 gallon batch of beer. (Yes Trillion)

Hmmm, maybe I've got some wrong information here but I was under the impression that a 5gal fermentation yields maybe about 1 trillion cells at the end of fermentation. How are you estimating 3-5 trillion in 3gal?

Estimated by doing a cell count of a representative sample with a hemocytometer. The cell concentration on my last batch was 1.4 trillion per liter, and it filled three quart size mason jars. Viability was 97% on that batch. Sometimes it's as low as 60% post fermentation.

If you pitch a beer of similar gravity onto a fresh cake, you will be over-pitching by about 4 to 6 times. The cake from a beer (any beer) will be roughly 6X the ideal pitching count. Accounting for dead yeast, you the amount might be down to 4 X (lots of variables in that).

Over-pitching can result in loss of yeast esters, and lower attenuation (using old yeast to complete the fermentation rather than freshly reproduced new yeast).

WoodlandBrew said:

Estimated by doing a cell count of a representative sample with a hemocytometer. The cell concentration on my last batch was 1.4 trillion per liter, and it filled three quart size mason jars. Viability was 97% on that batch. Sometimes it's as low as 60% post fermentation.

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Wow that's unreal. I wonder how other people compare. That makes me wonder about some of my own practices. I'm usually pouring a liter of sterile water onto my yeast cakes, swirling it up, and then pouring the slurry into two mason jars. I usually consider them to be about 500bn cells and mark them with a harvest date. Then when it's time to brew I'll use Mr Malty to estimate viability and then estimate what volume I would need to equal 100bn cells (i.e. one yeast pack with 100% viability), and then make a starter.

I guess it's possible that I'm overpitching, but my fermentations act the same as when I buy a new pack and make a starter with the first generation.

Overpitching is doable. I take great pains in trying to pitch accurate amounts. I use mr. malty and have found it to be reliable. I am looking for the textbook pitching rates most of us use, followed by a peak cell count at high krausen of about 30-40 mill/ml. One of the breweries I worked for with an annual output of 250,000 bbl a year was set on pitching cone to cone without taking cell counts at critical points in the fermentation. They were perplexed as to why the yeast was dropping like a stone and leaving behind copious amounts of diacetyl. I took a simple cell count at 18 hours showed a high krausen count of 80 mill/ml. The yeast was pooping out after competing for nutrients and sinking to the bottom. That is besides the issue of reduced final bitterness and massive beer loss to huge tank bottoms.

Wow I didn't know over pitching could even be an issue. I plan on brewing an Irish Red in a few weeks (est OG 1.056), then racking a Blue Moon clone (est OG 1.055) right onto that yeast cake. By this method I'd be grossly over pitching?

Maybe I'd be better off taking a liter of slurry from the cake and repitching into the blue moon clone?

You gotta check out a pitching rate calculator - you'd be surprised how little yeast slurry you actually need. Probably somewhere around a half cup but it's dependent on a lot of things like how much trub is in there, how tightly packed, etc.

Pitching on a yeast cake is the greatest crime that homebrewers regularly do. Don't do it!

Yes, you need very little, but keep in mind that pitch rate calculators are only providing a rough estimate. They can be off by a factor of ten pretty easily. IME the viability estimations and cell counts are much lower than the actual, so if you use the Mr. Malty calculator you will probably be over pitching, but that's generally better than under pitching.

See this for a detailed explanation:
http://woodlandbrew.blogspot.com/2012/11/counting-cells.html

Antler said:

Wow I didn't know over pitching could even be an issue. I plan on brewing an Irish Red in a few weeks (est OG 1.056), then racking a Blue Moon clone (est OG 1.055) right onto that yeast cake. By this method I'd be grossly over pitching?

Maybe I'd be better off taking a liter of slurry from the cake and repitching into the blue moon clone?

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I have found using about a quarter of a fresh yeast cake (for a similar gravity beer) is about the right amount. My logic, (very rough), is as follows. At the end of fermentation, a beer will have roughly 6X the ideal amount for pitching; assuming some loss in viability due to alcohol level and hydraulic pressure, I estimate there are about 4X live yeast left. Using a quarter of the cake, means you can simply estimate it regardless of the amount of trub.

If you are not ready to brew the day you bottle, slurry can be stored in the fridge for a week (actually longer) without issues. Just pour into sanitized containers (I use mason jars).

WoodlandBrew said:

Yes, you need very little, but keep in mind that pitch rate calculators are only providing a rough estimate. They can be off by a factor of ten pretty easily. IME the viability estimations and cell counts are much lower than the actual, so if you use the Mr. Malty calculator you will probably be over pitching, but that's generally better than under pitching.

See this for a detailed explanation:
http://woodlandbrew.blogspot.com/2012/11/counting-cells.html

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I did not check your link. I agree, Mr. Malty will probably result in over-pitching if you use slurry. I think it's estimate of yeast viability of stored slurry is way too low.