Do you raise or lower the temperature on a ale yeast to do a diacetyl rest?
I have a English Bitter sitting on Wyeast 1968 - London ESB Ale
Wy’s yeast strain info states: “Diacetyl production is noticeable and a thorough rest is necessary.”
I have only done diacetyl rests on lagers by raising the fermentation temperature.
The Fermentis “tips and tricks” document indicates that you decrease the temperature on a Ale to 60-62F for 24 hours to do a diaceytl rest. Is this true? should I chill the carboy?
Smoga,
How long are you keeping the 1968 in primary and at what temp do you ferment? With a big starter (like in a commercial brewery) this yeast will go to FG in 4 days, but needs 6-7 days to clean up completely. That is what Wyeast is talking about. If you are fermenting at 66-68 for 7 days or longer, you don’t have to worry about diacetyl.
My understanding is that while warmer temps are associated with higher levels of diacetyl production, it is also associated with a faster reuptake of diacetyl by the yeast cell where it is broken down. This is why lagers (which are fermented below 60 F) often receive a “diacetyl rest” where the temp is allowed to rise to 60 F. No need to do that for ales (which typically are brewed above 60 F), though.
I agree with the others. As long as you stay above 60 F you shouldn’t have to worry about diacetyl as long as you keep it on the ale yeast long enough for fermentation to reach completion and all the byproducts have a chance to get cleaned up.
BJCP style guidelines does say that diacetyl in very low amounts are OK for bitters/ESB’s. No diacetyl is better, IMO. Give it time.
And if you don’t actively control fermentation temp (i.e. keep it in the basement), just move it up stairs when you’re 2-4 points away from your target gravity.
No basement? You could use a Fermwrap with no insulation to raise the temp 5-10F, but its much less accurate.
go for a longer ferment. Give the beer some time after fermentation “stops”
The most common mistake I see new brewers make is to remove the beer from the primary too soon.
…and measure your gravity to calculate your attenuation. If the beer is nearly fully attenuated the yeast has flocculated and won’t be able to properly clean it up. The one thing I like to do is taste the beer to test for diacetyl.
This yeast strain is highly flocculant. This means most of the yeast is dropping out of suspension which is where it is needed if is to quickly reduce diacetyl as a normal part of fermentation. Yorskshire Squares and Burton Unions essentially do this by returning the krausened yeast to the beer keeping it in suspension longer. I’ve heard of commercial breweries bubbling carbon dioxide up through the conical to keep the yeast in suspension. You may also benefit from rousing the yeast, but that needs to be done quite often to be effective since the bulk of fermentation completes in a few days.
Give your beer sufficient time after it hits terminal gravity to ensure the yeast has a chance to reduce diacetyl. If you can detect diacetyl by aroma or flavor, you can sample the beer to ensure it is clean. Since it’s not highly carbonated, you should swirl your sample in the glass to release the aroma the carbonation otherwise would. This ensures you won’t be surprised later.
Lager yeasts are fermented much colder and often benefit from a raised temperature to aid diacetyl reduction. This is done after the major bulk of fermentation is complete such that off flavors aren’t generated due to higher temperatures during the primary phase of fermentation.
