yeast before or after?

[dickshindles]

I am curious to know who harvests their yeast (for re-pitching) before or after they crash their beers, and why.

I was taught to wait until primary fermentation is complete, and re-pitch to another vat before crashing the beer. It was shown to me as if there was no other way to do this. I now hear from others that they wait until after they crash the beer. I understand that it aids in flocculation to wait, but it was told to me that if you wait until the beer is cold, there are 2 problems. First, the risk of dead cells, and second, shock - going from 35 degrees to 70 degrees.
Please, explain the pros and cons of both.

The Dickster

[MatthewS]

I have always harvested yeast after primary in complete.

What we do here is...

Ferment completely, rest for 24-48 at 63-70(beer dependent)
Crash to 55 for 36 hours... crash to 50 after a full 24 hours... harvest the yeast... and this is usually a brewday so.. pitch it right in at knockout.

With our yeast, I dont think I could ever get a decent harvest at 65+F... what are you using that flocs out enough to get a harvest that is worthy of pitching?

[wailingguitar]

When harvesting from unitanks I have always pulled from the bottom after the crash cool has taken place. The only time I have done anything different was at one brewerry with open fermenters... we would "top-crop" the yeast, by hand with stainless ladles, into stainless buckets, which were immediately dumped into the next fermenter.

[monkeybrewer]

yeast harvest

I harvest yeast after primary fermentation and after quickly crashing it. I'll ferment my ale yeast at 67 F (it's the WYeast 1056 strain). It will usually finish in 72 hours(sometimes quicker). After that, I let it remain at 67 F until the end of the 6th day so the yeast will scavenge all of those nasty off-flavor precursors (basically a long diacetyl rest). I then cool it to 32 F over night and harvest the next day. This is how I've done at the 4 breweries I've worked for and we always had great results. I have shared your concern in the past about "shocking" the yeast by crashing it too quickly. Or letting the yeast sit on the beer for a moment after primary fermentation is complete due to literature put out by the yeast companies. The one thing I can say is; in absolutely going against the literature (even harvesting 3-4 days after crashing), the breweries I've worked for have always maintained viability counts in mid to upper 90%. I'm not sure why the yeast companies have such a drastically different protocol than that of what is so effective in practice in the field. If anyone knows why there are so many differing opinions I would love to know. anyways...
Cheers

[dick murton]

The time / temperature to crop yeast is largely dependant upon the yeast strain. Some yeast strains autolyse very quickly once the main fermenation is over, unless they are cooled quickly. Others seem to be more robust. I suspect a lot of advice from the yeast suppliers is based on very large scale brewing, where the sheer mass of yeast means heat transfer to the cooling jackets is very poor, and the yeast can autolyse quite rapidly. Some yeasts flocculate more readily than others, so a highly flocculant yeast should normally be cropped warmer than a poorly flocculating yeast

My suggestion is to crop the yeast as soon as it has flocculated such that the yeast slurry consistency will only increase very marginally, and then to cool it as rapidly as possible if there is a delay before repitching. Normally, for a bottom cropping yeast yeast, this will be after cooling. Top cropping yeasts will probably be whilst at or close to top heat so that it doesn't drop like a stone to the bottom.

I wouldn't worry about temperature shock - a change of 1 or 2 deg C per hour isn't going to shock it. To transfer it through a chiller and do it in a few seconds may be different, with which I have no experience.

Cheers

[MikeJordan]

I think Dick has summed up the yeast cropping strategy well. My experience has always been to harvest yeast after the tank has been crash cooled. The majority of FV's were CCT's. On rare occasion a "warm harvest" has been necessary due to yeast availability. The results of warm harvesting have been mixed and most often followed by a sluggish fermentation and slow VDK reduction. I really believe it depends upon the yeast strain but most likely the yeast to flocculate first isn't the best choice for repitching...unless you're selective cropping to change the flocculation characteristics! Of course yeast vitality and viability should also be considered regardless of your yeast cropping technique.

[liammckenna]

With true 'top croppers', I like to harvest to harvest near the end of primary, say, 2oP from terminal gravity.

Using sanitized stainless buckets with tight fitting lids and a positive displacement pump like a rotary pump, I vacuum the yeast of the fermentation through the top manway into the buckets.

Usually end up with enough extremely vigorous yeast to start another three or four brews. I find that the rise this late in the fermentation is vigorous and extremely clean vis-a-vis contamination. I also re-propagate every 10 generations from a known stock culture.

That being said, there is some argument to suggest that within each crop there are actually a great deal of different sub-strains with differing flocculation characteristics. Harvest too early and you'll miss those non- or poorly flocculent sub-strains. The best long term way to maintain your strain characteristics is to bottom crop from the middle layer of the cone, wash (if contamination may be an issue) and repitch as soon as possible. Given attemperation has been gradual, as Dick suggests, temperature shock should be a complete non-issue.

[Woolsocks]

asap

I was taught to harvest yeast "as soon as it's practically possible" after fermentation is over. When this is depends on your yeast strain, the type of tank (conical, open, flat-bottom, etc.) and your fermentation practices.

[Woolsocks]

This might also be handy. I more-or-less follow the advice here and it has served me well:

http://brewingscience.com/yeast_care.htm