How much is too much yeast?

[syncopadence]

I'm making a 5 gallon batch with 12lbs of grain, 2.5oz of chocolate (doesn't show sugar content), and 8oz coffee beans (if that matters).  I'm going to use Safale US-05 dry yeast and rehydrate, which has about 180 billion yeast cells.  With all that sugar, should I use 2 whole packets of yeast and pitch into primary? Without the chocolate in the recipe, Beersmith says I should be using just over 200 billion yeast cells for the recipe, and recommends two.  But would using 2 whole packets be overpitching then?
Thanks for any help in advance.

[mainebrewer]

At 75% system efficiency, the OG will be around 1.065. I don't know how fermentable the chocolate is.
But I think that one 11 gr packet of US05 will be plenty of yeast.

[homoeccentricus]

Could I semi-hijack this thread and ask a similar question? Is it actually possible to pitch too much yeast? Say, pitch a whole lot of slurry from a previous batch into a new, smaller batch? What would be the side-effect(s)?

[David Lester]

I would use two packets, and no it's not over pitching. I have used yeast that was less than recommended by my software, which resulted in off flavors, but haven't seen any problem with too much yeast other than drying it out (way more than 2 packets worth). Years ago I read that if there was too much yeast, the beer would ferment out too quickly and you wouldn't get the character of the yeast. But after pitching huge amounts of slurry yeast, I found the beer comes out dryer, but has plenty of the yeast character. If you want a malty beer that isn't too dry, you should use the Yeast Calculator.

[brewinhard]

At a 1.065 OG you will have no problems with 1 packet of properly rehydrated US-05 given the right amount of aeration.  I have used up to 1 packet rehydrated for a 1.075 OG for IPA's before with no issues whatsoever (providing the packet isn't past it expiration date). 

And as far as overpitching is concerned, IFRC, I have read about issues affecting the body of the beer and with underattenuation due to lack of yeast growth and healthy new cells being produced that won't finish the job.  Maybe someone with some other observations will chime in here.

[dilluh98]

And as far as overpitching is concerned, IFRC, I have read about issues affecting the body of the beer and with underattenuation due to lack of yeast growth and healthy new cells being produced that won't finish the job.  Maybe someone with some other observations will chime in here.

I have heard this line of reasoning as well. Slightly (or even grossly) under-pitched but exponentially growing yeast cells will do as good or better than "too many" yeast cells with no chance to grow.

[ynotbrusum]

At a 1.065 OG you will have no problems with 1 packet of properly rehydrated US-05 given the right amount of aeration.  I have used up to 1 packet rehydrated for a 1.075 OG for IPA's before with no issues whatsoever (providing the packet isn't past it expiration date). 

And as far as overpitching is concerned, IFRC, I have read about issues affecting the body of the beer and with underattenuation due to lack of yeast growth and healthy new cells being produced that won't finish the job.  Maybe someone with some other observations will chime in here.

I think it has more to do with fewer life cycles in the course of depleting the available nutrient for the yeast.  Kind of like too many guests and not enough food - the yeast chews through it without going through as many life cycles as would happen with an optimum pitch rate.

Attenuation is merely the measurement of residual sugars which likely would be just as great under any circumstance - the yeast will consume all available nutrients that it is capable of metabolizing in either event.  Just with the overpitch there are more unhappy guests that are disappointed that the buffet ran out earlier than optimum.  The beer that I over pitched was okay, but generally described as more lifeless and expressionless than prior batches of the same thing that were pitched closer to optimum.  Remember, however that we don't use a hemocytometer, so we don't have actual yeast counts to dial in our pitches.  We rely on things like Mr. Malty and prior experiences.

[klickitat jim]

How much yeast is one of those questions in brewing that has a wide variety of possible answers. It depends on what results you desire. How much is needed to make alcohol and CO2? One healthy cell. Can you pitch so much that it won't make alcohol? Probably not, unless it's like two pounds of dry yeast into a pint of wort. It would just make a mess.

In reality, I pitch a little less than normal if it's a small beer or if I want more flavor expression. A little more than normal if it's a bigger beer or I want a cleaner lower level of flavor expression. Warmer gets less, colder gets more.

[morticaixavier]

the other concern with over pitching is acetaldehyde. If the fermentation takes off too quickly and finishes too quickly the yeast will run out of carbon fuel before they can clean up their own bi-products.

[BrewBama]

This is a very timely discussion. I am brewing today and plan to pitch US-05. I have two packs but I think i'll hydrate one and keep one as the emergency back up pack.

[duboman]

I've always related over pitching to the reality of real life work. If you throw too many bodies into a project only some of the labor is productive and the rest just watch, cost you money and show no results in the end. The perfect sized labor force gives you the best return on your investment:)

[brewinhard]

The perfect sized labor force gives you the best return on your investment:)

Even if that labor force is microscopic!