Yeast performance

Hi!
I am an all grain brewer, brewing in batches of 5 gallons. After several years of successful brewing of lighter ales (4.5 - 5.5%), I have recently encountered some problems with yeast performance in my wort. After a reasonable (rather than a strong) primary fermentation, I find that the fermentation comes to a complete stop when the gravity reaches about 1020 (or higher) and this tends to happen after only two days. The problem seems to be the same whether I use a yeast recovered from bottle conditioned beer or a commercially produced yeast for homebrewers, such as "Safale". I also pitch a relatively high quantity of yeast, rather than relying solely on the meagre contents of one sachet. Interestingly, I did not get the problem when I used a homebrew kit rather than a full mash. I am looking for suggestions as to what might be going wrong. It seems to me that the three things it could be are 1) insufficient oxgenation (how should I oxygenate after letting the wort cool naturally overnight?) 2) problems with "fermentability" of the sugars obtained from the mash process 3) bacteria problems. Any thoughts would be most welcome - I am really hoping I can find a way past this rather depressing problem.
Thanks
Craig, the Bothy Brewer

Well, the first thing that comes to my mind is the temperature of the mash. How accurate is your thermometer, and at what temperature do you do your mash? How hot is you mash water, and at what temp do you hold it at?

The other thing that probably doesn't have to do with this issue but struck me is letting the wort chill naturally overnight. That's really not a great idea. But if you don't have off-flavors or infection it's working for you. I would think you wouldn't get any cold break by not chilling the wort, though.

Oxygenation can be an issue. I chill my wort in about 20 minutes after the boil, then I pour through a strainer and splash lots. Then I also run an aquariam pump for about 30 minutes before I pitch the yeast. If you're covering the wort and letting it chill overnight, you're not oxygenating.

Maybe just those two things (mash temp) and not oxygenating might be the problem. I wonder why this isn't a problem with the kit beers, though.

Also note that safale does not have the attenuation that some yeasts due, such as nottingham.

I'd definitely check your mash temperature first though

To expand upon Yoop's post, you may want to Iodine tests on your wort to ensure that you're converting to sugars. Sounds like you're getting a lot of dextrines. Either you're pitching too high or too low, and since you didn't mention astringent flavors I'm guessing too cold.

I agree. It sounds like a conversion problem, so look into your mashing protocol. If you let us know more detail about what you're doing, that can help.


TL