Do ales from an extract kit need a diacetyl rest?

[pc_trott]

I've been reading Papazian's "Complete Joy of Home Brewing" and Palmer's "How to Brew" in an attempt to make some sense of kit instructions, and I am now suffering from information overload. Both books give a cursory overview of the diacetyl "butterscotch" flavor, but neither book goes into the subject in enough detail to be really helpful to a beginner.

I did a search on the forum, and the strings I came across on the subject seemed to imply that diacetyl off-flavors were mostly a lager problem. I don't have a refrigerator to ferment at low temperatures, so I've been making only ales.

I ferment in a cool basement, and I've got a heating wrap for my carboy. The ambient temperature is currently around 60F. I've been turning the heat up to 70F for a day when fermentation slows down to around one burp from the airlock every 20 seconds. I leave it there for ~24 hrs, then let it go back to ambient. Somewhere in the forum I read something that made me think this was a good idea. (That's what I get for doing my own thinking.)

Question(s): Do ales need a diacetyl rest, or is it only a lager problem? If ales need a diacetyl rest, how long should it be, and at what temperature? Does it depend on the type of ale?

 

[VikeMan]

Question(s): Do ales need a diacetyl rest, or is it only a lager problem? If ales need a diacetyl rest, how long should it be, and at what temperature? Does it depend on the type of ale?

Diacetyl is not only a lager issue. Every yeast strain makes diacetyl's precursor, and some are more efficient at cleaning up diacetyl once it's been made. But generally with ales, a few days in the fermenter after the beer has reached terminal gravity is enough, even without increasing the temperature. That said, diacetyl is converted and cleaned up faster at higher temps.

 

[Bobby_M]

Diacetyl is a naturally occuring compound created during all fermentation. Some yeast strains product more than others. All yeast, if they are healthy at the end of fermentation will consume most of it. If the yeast is prematurely removed or floc out too soon due to a slight temperature decrease, it can remain in the beer. I ALWAYS bump the temperature upwards 1-3F during the last few days of fermentation and hold it there for another week.

 

[Birrofilo]

I did a search on the forum, and the strings I came across on the subject seemed to imply that diacetyl off-flavors were mostly a lager problem.

The reason why this concept is put forward is that lagers being "cleaner" they somehow denonciate any defect more clearly than ales. Ales are usually more complex in aromas (you want fermentation aromas) and often are also more complex in the malt dimension (think porters) and this makes diacetyl less evident when present. Also, a little diacetyl is considered by many as being not necessarily detrimental in some ale styles, English ales in particular.

That said, diacetyl is a product of the fermentation and doesn't depend on whether you ferment from extracts. Also, diacetyl is diacetyl so if you don't like it and can "spot" it you won't like it in an ale either.

I am not sure if diacetyl is what I think it is, but I rememeber a couple of stouts (from extract) that I liked better when they were younger than older, because they had that butter hint, I think that was diacetyl, but it was a gentle pleasant note. I was never able to spot it in a commercial lager but some people smell it in Pilsners.

 

[IslandLizard]

I've been turning the heat up to 70F for a day when fermentation slows down to around one burp from the airlock every 20 seconds. I leave it there for ~24 hrs, then let it go back to ambient.

Raising the ferm temps toward the end of fermentation (when fermentation slows, krausen starts to drop, airlock activity slows down, etc.) is good. But you need to keep the higher temps on (or even ramp up a few degrees over as many days) until fermentation has definitely finished. Then leave it at that for an extra 2 days or so. Dropping temps before that point, is counterproductive, and may result in more off-flavors than just leaving it be. Especially when they drop back down to 60F.

60F is pretty darn low for ale yeasts...

 

[pc_trott]

Dropping temps before that point, is counterproductive, and may result in more off-flavors than just leaving it be. Especially when they drop back down to 60F.

Yikes! I just turned it down on the stout I'm brewing. I'll turn it back up post haste! Thanks!

 

[IslandLizard]

Yikes! I just turned it down on the stout I'm brewing. I'll turn it back up post haste! Thanks!

The heating wrap around the fermenter, is it temp regulated?
How do you monitor the actual temp of your (fermenting) beer?

Re: 60F ambient.
What yeast are you using?

 

[Qhrumphf]

It's not coincidental that beers that have historically had diacetyl (namely ales from the British Isles) also tend to use very flocculent yeasts. By dropping out very quickly after a rapid fermentation, they often don't take up as much residual diacetyl before going dormant and leave more in the finished beer as a result.

A drop in temp can often cause these yeasts to flocculate even faster, and lead to an even higher diacetyl character.

In other words, in addition to lagers English yeasts will also benefit from a boost in fermentation temp at the end of fermentation.

 

[pc_trott]

The heating wrap around the fermenter, is it temp regulated?
How do you monitor the actual temp of your (fermenting) beer?

Re: 60F ambient.
What yeast are you using?

The heating wrap is temp regulated; I got it from Northern Brewer, and it includes an LED readout that tells the current temp of the carboy and the set temperature. It has a sensor that I've attached to the outside of the carboy and covered with a layer of styrofoam. I use the current temp on the readout to monitor the actual temp. When the beer is fermenting, the readout is six to eight degrees warmer than ambient, which I am reading from a thermometer that is not attached to the carboy.

The yeast is Safale S-04.

 

[IslandLizard]

These things?
https://www.northernbrewer.com/products/fermotemp-electric-fermentation-heaterhttps://www.northernbrewer.com/products/northern-brewer-dual-stage-temp-controller
Then you're at least not trying to ferment with S-04 at 60F. Phew, that's a relief!

But now it looks you're slowly trying to "heat up" your basement with it.
I doubt it's turned off more than half the time like that, at 35W.

After the first few days (to a week), when things slow down, the exothermic part of (early) fermentation is over.
At that point, think about wrapping that whole system with some insulation. A few layers of bubble wrap or Reflectix would do it. Put also some insulating foam for the bottom to sit on.

 

[Dland]

My guess is that w S-04 at that temp, you probably do not have to worry about excessive diacetyl.

 

[pc_trott]

At that point, think about wrapping that whole system with some insulation. A few layers of bubble wrap or Reflectix would do it. Put also some insulating foam for the bottom to sit on.

Doh! Why didn't I think of that?!? (Don't tell me, it wouldn't be polite of you...)