Diacetyl and the d-rest

[The-Engineer-That-Brews]

Great post by White Labs on where diacetyl (butter/pocorn flavour) comes from and how to control it: Compound Spotlight: Diacetyl.

(EDIT: there is another good post on the same topic here)

In summary:

Where diacetyl comes from​

• Diacetyl comes from a chemical called ɑ-acetolactate that the yeast makes internally in order to grow.
• Some of the ɑ-acetolactate leaks into the beer, where it oxidises to form diacetyl.

How much of it is produced​

• The yeast only produces ɑ-acetolactate while it's in exponential growth mode (roughly < 24hrs after pitching).
• Yeast produces more ɑ-acetolactate when it's 'hungry', so it can help to add nutrient to low gravity wort (see: FAN - it's what beer craves)
• The less ɑ-acetolactate the yeast makes, the less diacetyl you have to get rid of.

Where it goes​

• The yeast always produces ɑ-acetolactate so you always get some diacetyl in the beer.
• Fortunately when the yeast has run out of other things to 'eat' (but not before) it will re-absorb diacetyl and convert it into stuff you can't taste.
• Raising the temperature near the end of a cold fermentation (last 10 SG points / 3º Plato) encourages the yeast to snack on the diacetyl before it goes sleepy-bye.
• An appropriate kind of temperature for a d-rest is about 18ºc, but don't raise the temp too suddenly.
• Don't cold crash too early: the yeast may not yet have processed all the diacetyl even if there are no visible signs of fermentation.

 

[Tess Tickle's Brewery]

Thanks for this TETB, it's really interesting.

This explains why I had to throw down the sink two batches of rye IPA, because I underpitched US-05. I'm guessing the growth phase made it work harder than usual, causing in my case, an oil slick lol

 

[hoppyscotty]

Everyone seems to be in a big rush when it comes to beer. I'll always leave it for a week at least once I think fermentation has completed and start to slowly ramp up the temp over that time and usually can squeeze out an extra gravity point and gives it plenty of time for D-rest. Patience is a virtue with these things...if you're worried about running out of homebrew then get a second fermenter

 

[Tess Tickle's Brewery]

Everyone seems to be in a big rush when it comes to beer. I'll always leave it for a week at least once I think fermentation has completed and start to slowly ramp up the temp over that time and usually can squeeze out an extra gravity point and gives it plenty of time for D-rest. Patience is a virtue with these things...if you're worried about running out of homebrew then get a second fermenter

I do this too unless it's very hoppy and needs to come off them. When it goes in secondary it sits for another week before kegging.

I leave lagers in the fermenter for three weeks.

 

[hoppyscotty]

Time is our best freind. On the odd occasion I've rushed a beer I've usually used a Kveik yeast or fermented under pressure and managed to get away with it. But not quite as good or rounded as a beer that hasn't been rushed.

But the change I've made recently is to ensure I over pitch. After messing around with various yeast pitch rate calculators from the main yeast manufacturers the usual 11g packet of yeast isn't quite enough for a 19 litre batch - usually 1.5 packets is required so I'll round up. OK the cynics might say they're just trying to sell more yeast, but there are non-yeast manufacturer calcs out there that all agree closely enough. Though I've never produced a beer that has suffered from the classic symptoms of under-pitching, I do religiously use yeast nutrient so maybe I've just been getting away with it with the combination of use of nutrient and giving the beer plenty of time.

 

[The-Engineer-That-Brews]

the change I've made recently is to ensure I over pitch

Many people would agree, although sometimes I worry that a badly made starter just contributes a lot of very tired yeast.
Also I know one should take some of the Brülosophy-style comparative experiments with a pinch of salt, but IIRC the under/over pitch ones I have seen were inconclusive

 

[Sadfield]

Everyone seems to be in a big rush when it comes to beer.

It's the cold crash, fast carb, grain to glass generation. Maturation feels like a forgotten concept. 2+2+2 doesn't get quoted any where near as much.

 

[Tess Tickle's Brewery]

These days I go with what Brewfather tells me and it always goes well. My lager in the fermenter at the minute has three packets of dry yeast in. I don't like doing starters and prefer to pitch dry yeast. My beer has massively improved since I started doing this.

 

[The-Engineer-That-Brews]

I do this too unless it's very hoppy and needs to come off them. When it goes in secondary it sits for another week before kegging.

I leave lagers in the fermenter for three weeks.

Have you tried the method where you start ramping up the temp for the second half of fermentation Tess? I’ve done it a couple of times and it seems to be great for reducing the maturation time

 

[Tess Tickle's Brewery]

Have you tried the method where you start ramping up the temp for the second half of fermentation Tess? I’ve done it a couple of times and it seems to be great for reducing the maturation time

I'm actually doing that at the moment with my lager. It's had 6 days at 10c, now it's on its 2 days at 13c, then 1 day at 17c and 1 day at 19c, as per the Brewfather profile (and David Heath).

I'll leave it at 19c for a long while.

Going back to your original point TETB, I can't smell any diacetyl at all as I pitched the right amount of yeast. Normally if it's there it's very strong for my particular nose.

 

[hoppyscotty]

These days I go with what Brewfather tells me and it always goes well. My lager in the fermenter at the minute has three packets of dry yeast in. I don't like doing starters and prefer to pitch dry yeast. My beer has massively improved since I started dong this.

I agree. Dried yeast is literally the best thing than sliced bread. Not sure how the economics work out as you scale up but just don't see the point in faffing about. Also I've had better results when I've used the dried version of a liquid yeast. Not sure if this is my ability to make a starter or not....don't see why it should, I've followed all the instructions, but always managed to get more hop character out of dried yeast.

Have been tempted to go back to making starters using those cans of wort...but they are really expensive so not bothered as yet.

 

[Tess Tickle's Brewery]

I agree. Dried yeast is literally the best thing than sliced bread. Not sure how the economics work out as you scale up but just don't see the point in faffing about. Also I've had better results when I've used the dried version of a liquid yeast. Not sure if this is my ability to make a starter or not....don't see why it should, I've followed all the instructions, but always managed to get more hop character out of dried yeast.

Have been tempted to go back to making starters using those cans of wort...but they are really expensive so not bothered as yet.

I also wonder if when using liquid yeast and making starters, people are losing the precious first 24/48 hours worth of esters (on certain types of yeast) as you're throwing some of it out. Hope that makes sense.

 

[hoppyscotty]

I also wonder if when using liquid yeast and making starters you are losing the precious first 24/48 hours worth of esters (on certain types of yeast) as you're throwing some of it out. Hope that makes sense.

Sounds like a topic of a Doc Anna Phd thesis

 

[Tess Tickle's Brewery]

I think too much

 

[The-Engineer-That-Brews]

Going back to your original point TETB, I can't smell any diacetyl at all as I pitched the right amount of yeast. Normally if it's there it's very strong for my particular nose.

Well I've tasted a few of your beers and they've all been well made ;-)

Apparently a good way to check for diacetyl is to do a "forced test": decant some of the beer and stand it in hot (60ºc) water for 15-30 mins to speed up the oxidation.
Then if it's there you'll really smell it.

 

[Tess Tickle's Brewery]

I'm far too lazy for that I'd just rather wait

 

[Alan_Reginato]

It's just wait. Let it sit for 3 to 4 weeks and take samples weekly. You will taste the difference. No overpitch needed.

Now, that thing "X days grain to glass", is a crime against homebrew. Beer need a maturation time. Don't even talk about Kveik nonsense. Even NEIPA'S, and equals heavy hopped beers, can be improved by a longer fermentation. It's just a matter to adjust the timing of dry hopping. A day before cold crash and kegging (or bottling).

 

[Sadfield]

Yes, I don't brew NEIPAs, but from brewing West Coasts, I strongly suspect that you don't need 3kg/l of cryo hops if you are dry hopping a more stable beer.

 

[JockyBrewer]

I also wonder if when using liquid yeast and making starters, people are losing the precious first 24/48 hours worth of esters (on certain types of yeast) as you're throwing some of it out. Hope that makes sense.

Level of ester production is mostly related to the amount of yeast growth. The usual 1-2 litre starter will not actually have enough cells to ferment a 23 litre batch, so it'll still require growth and you still get esters.

Luckily it's very hard to overpitch yeast. The only time you're likely to do it is when reusing a large portion of a yeast cake for a moderate strength beer. In that case you don't get much, if any growth, so end up with a much reduced fermentation character.

 

[Tess Tickle's Brewery]

Thanks JB that's fascinating!