# Is my lager ready for a diacetyl rest?

Hello I have a lager than been fermenting for 10day’s now ( OG is 1.050 the FG is 1.013). Now if my math skills are still has good as they were (it’s been 20yr scent I was in math class) I take 1.050 subtract 1.013 which would be 0.37 divide than by 3 which is 12.3333333 now hear the ? the 12.33333333 do I keep the 12.33333333 or just round it off to 13? Basic do I do 1.050 subtract 1.013 =37/3=12.333333333 +13= 25 so i guss I do the diacetyl rest at 25 than rigth ?

Ahhhhhh- Math :lol:
Here’s my way to figure it: 50-13=37. 75% of 37=28. 50-28=22. So if I actually did my D-rests based on the 3/4 of the way to FG rule, I would warm her up at 1.022.
But after the 1st one a couple years ago, I don’t bother. I do my D-rests when the visible signs of fermentation are starting to slow. Usually have been around 7 days in. I don’t believe there’s any problem if you warm things up too early, provided the 1st couple of high-fermentation days are over. If my fermentation temps have been in the 45-50* range, I’ll warm her up to the low 60s( basically moving the bucket from my cold garage to my less cold basement). I’ll leave her there for a week and take an SG. If it’s done I rack to a carboy and move her back out to the garage in a swamp cooler filled with water(which often turns to ice) and leave it alone for 6-8 weeks.
I do 3 lagers each winter. This year temps have stayed low for so long, I should have done 5 or 6.

How does one calculate where 75% for the diacetyl rest?

You don’t, just let it warm up to 60-65F when you start to see signs of fermentation slowing, as JimRMaine said, usually around 5-7 days, let go another week, then keg it (at least I do…).

I am guessing that 75% completion of the fermentation is where the DA Rest would be most appropriately considered.

Me personally, I like to simplify things and usually ramp up my temp after roughly two weeks. I also like to ferment on the cold side of the yeast’s tolerance too. With that in mind it takes a little longer to complete.

My schedule for a yeast that would require a DA rest (e.g.: Wyeast 2308):

Shift down from 60* (pitching temp) to 48* and hold for 12 days
Shift up to 68* over a two days (about a 10 degree swing per day) and hold for a week at 68*.

At that point I check the gravity and taste the sample to see if I can detect and diactyl. If not, Keg and drop down to 35 and hold for about five weeks.

If I do detect DA, or not at my terminal gravity, I’ll leave it a little longer at the higher temp.

Other than that, you lost me at “math” lol.

Cheers!

:cheers: