[narcout]

Anyway here's a 2008 paper suggesting that pitching rate makes very little difference to flavour, except for diacetyl level rising with high pitching rates (http://www.ncbi.nlm.nih.gov/pubmed/19018524).

This one came to opposite conclusion regarding diacetyl, though it was studying high gravity fermentation with lager yeast. 

I think this stuff is interesting and fun to read, but I don't know if it is all that relevant to what I'm doing. 

"As expected, increasing the pitching rates led to faster fermentation rates and higher yeast cell counts. Formation of 2-methyl-1-propanol increased with increasing pitching rate, but the formation of 2- and 3-methyl-1-butanol decreased.  The pitching rate did not alter ester formation in these experiments, with the exception of isoamyl acetate, where the level declined with an increased pitching rate.  Lower pitching rates led to higher levels of diacetyl and 2,3-pentanedione. The effect of pitching rate on flavour compounds clearly merits further investigation."

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2007.tb00259.x/pdf

[charles1968]

Anyway here's a 2008 paper suggesting that pitching rate makes very little difference to flavour, except for diacetyl level rising with high pitching rates (http://www.ncbi.nlm.nih.gov/pubmed/19018524).

This one came to opposite conclusion regarding diacetyl, though it was studying high gravity fermentation with lager yeast. 

I think this stuff is interesting and fun to read, but I don't know if it is all that relevant to what I'm doing. 

"As expected, increasing the pitching rates led to faster fermentation rates and higher yeast cell counts. Formation of 2-methyl-1-propanol increased with increasing pitching rate, but the formation of 2- and 3-methyl-1-butanol decreased.  The pitching rate did not alter ester formation in these experiments, with the exception of isoamyl acetate, where the level declined with an increased pitching rate.  Lower pitching rates led to higher levels of diacetyl and 2,3-pentanedione. The effect of pitching rate on flavour compounds clearly merits further investigation."

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2007.tb00259.x/pdf

If you dig around for the few published scientific studies, you'll find conflicting results but next to no evidence for a consistent effect on flavour. I think the take-home message is that advice on pitching rate is likely to be another brewing myth waiting to be properly debunked.

You're right that it might be specific to particular strains. Until better evidence comes in, however, I'm going to continue disregarding all advice on pitch rates and pitching rate calculators. I've always thought estimated cell counts are wildly inaccurate anyway. And if you pitch a starter into the main wort, all the supposed flavour benefits of high pitch rate go out of the window anyway.

[narvin]

The benefit I see from using some kind of calculator is consistency and repeatability.  You may not know how many cells you're truly pitching until you do a cell count, but your process is the same each time.  Of course, pitching a single smack pack is repeatable as well, but I find I get better results with a starter.  YMMV.

[charles1968]

There's certainly no harm in trying to be consistent. I do wonder if it matters as much as people claim though. Yeast multiply until they've consumed all the sugar and then drop out. It happens every time, however many you start with. I haven't seen any compelling evidence that the starting number affects flavour, but I accept that it's possible.

[klickitat jim]

Since we're on the subject. Is cold crashing considered yeast abuse? Guilty!

Some time ago I caught a Brew Strong episode where Jamil said that he read a study while working on his yeast calculator that chilling rapidly causes yeast to express 30% more esters. He didn't reference the study. I vaguely remember us talking it up here on the forum with many folks agreeing and some disagreeing. I was in the disagree side but admit that it could be my lack of detection skills.

Just recently I heard him reference this study again on a Jamil Show episode. He still didn't reference the study, but he did provide some additional info about it. Someone asked him how fast is too fast and he said that the study claimed you can chill 2F per hour without getting any negative effect.

So, when I cold crash, there are two 6 gallon batches in my temp controlled chest freezer and I simply change the setting to 30F. It takes at least 24 hrs for the steadily running chest freezer to drop from 72F (ale final temp) to 30. 42 degrees in 24 hrs is less than 2F per minute. With lagers, 68F D rest to 30 is only 38F in 24 hrs. Apparently I'm not detecting extra esters because even when I let er buck I'm not chilling fast enough to get greater than 2F per hour.

Proof that sometimes a little info = worrying about nothing.

[denny]

There's certainly no harm in trying to be consistent. I do wonder if it matters as much as people claim though. Yeast multiply until they've consumed all the sugar and then drop out. It happens every time, however many you start with. I haven't seen any compelling evidence that the starting number affects flavour, but I accept that it's possible.

Ya know, Charles, I was about to say I agreed with you until the bolded part.  I can't agree with that.  If it was true, you'd only need to pitch a single yeast cell.  I think consistency of results is a good thing and it's what I aim for.  But I've also found that you have a lot of leeway in the constituent parts that make up the result you want.

[charles1968]

Proof that sometimes a little info = worrying about nothing.

Yes I think I tend to overthink everything and I suspect other brewers do too, but maybe overthinking is part of the fun.

[RPIScotty]

Proof that sometimes a little info = worrying about nothing.

Yes I think I tend to overthink everything and I suspect other brewers do too, but maybe overthinking is part of the fun.

I'm an engineer. I can't get anything done unless I've invested at least 4 hours into overthinking it.

[denny]

Proof that sometimes a little info = worrying about nothing.

Yes I think I tend to overthink everything and I suspect other brewers do too, but maybe overthinking is part of the fun.

I used to overthink things, than with experience I found that there are so many things that just don't matter, or matter only in a general sense.  Pragmatism became my rule and it's served me well.  But this is a hobby and if you enjoy the overthinking part, be my guest.  Personally, I have other things to expend my brain on!

[charles1968]

Ya know, Charles, I was about to say I agreed with you until the bolded part.  I can't agree with that.  If it was true, you'd only need to pitch a single yeast cell.

That's where you start needing laboratory techniques - isolate a single cell on a plate and step up, keeping everything completely sterile. Possible but not a standard homebrewing technique and not very quick.

If you think of wort as a battleground in which all sorts of unseen microbes compete, then pitching a healthy population that gives yeast a headstart over bacteria or wild yeast makes perfect sense. A lag of a week or so is too long - you want yeast to poison the wort with alcohol and acid quickly so bacteria don't get a toehold. But as long as you pitch enough for that, I don't think adding more makes any difference.

I can't think of a time underpitching has given me any problems. Even with lager. Actually, pitching rate is probably least important with lager (unless you're a commercial brewery) as the low temp stops bacteria and nonlager yeast growing.

[charles1968]

I'm an engineer. I can't get anything done unless I've invested at least 4 hours into overthinking it.

It's a great trait in some walks of life. The same can be said for anxiety - a great characteristic for people who manage risk.

As long as you don't resort to spreadsheets when deciding what pair of jeans to buy...

[klickitat jim]

I feel a challenge coming!

1 gallon batches- something that doesnt require much work or hops, like an extract blonde.
One gallon fermented with Mr Malty calculated slurry amount
One gallon autoclaved and aseptic transfer pitched with a single colony. (Unless you have a scope to grab a single cell, but I think a tiny single colony ought to prove the point)
Blind Triangle test

The trick would be to also autoclave your oxygenation wand...

[Joe Sr.]

There's certainly no harm in trying to be consistent. I do wonder if it matters as much as people claim though. Yeast multiply until they've consumed all the sugar and then drop out. It happens every time, however many you start with. I haven't seen any compelling evidence that the starting number affects flavour, but I accept that it's possible.

Ya know, Charles, I was about to say I agreed with you until the bolded part.  I can't agree with that.  If it was true, you'd only need to pitch a single yeast cell.  I think consistency of results is a good thing and it's what I aim for.  But I've also found that you have a lot of leeway in the constituent parts that make up the result you want.

IME under pitching a high gravity beer will lead to under attenuation.

So I agree with Denny that the yeast don't necessarily consume all the sugar before they drop out.

But I also think you need proper aeration and consistent fermentation temp ( ie no temp swings).

More importantly I think thy you need to know how your yeast performs. I use the same four or five strains regularly and repitch until performance changes. Sometimes it's flocculation. Sometimes it's attenuation. No infections yet from this practice.


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[charles1968]

IME under pitching a high gravity beer will lead to under attenuation.

So I agree with Denny that the yeast don't necessarily consume all the sugar before they drop out.

But I also think you need proper aeration and consistent fermentation temp ( ie no temp swings).

If you ferment under an airlock, don't aerate, but also underpitch, a stuck ferment is very likely with British yeast strains. But the real problem in that case is ergosterol running out. Most British homebrewers use buckets with loose fitting lids, which reduces the need to aerate, but we still get stalls sometimes. I think the same issue explains the DuPont stall, rather than the much blamed back pressure.

Likewise some ale yeasts shut down after a sudden temp drop. That can happen whatever the pitch rate.