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Dawson's multi-grain -- missed O.G

Hey all,

I’m new to all grain. Today was a beautiful day in Conn so I took some time to brew my second match of AG. NB kit – thanks to Mister Dawson.

I have a 15g brew kettle, so I had a boil volume of about 7.25g. Boiled off at least 2 gallons. Ended up with an OG of 1.034 instead of 1.044. What have I done wrong?


For starters, are you accurately measuring the volume and gravity? Have you calibrated your instruments?

Did you hit the expected OG on your previous batch?

The number one factor in efficiency is crush. Was the same mill used to crush both grists?

sounds like you might have too aggresive of a boil if you boiled off 2 gal.

I’m doing a 5gallon batch with a 15 gallon kettle. Nice big surface area so I was not surprised by the 2 g but you might be right. Not sure how that impacts my OG. I would have thought It would have the opposite affect (a higher than expect OG instead of lower than expected). How does an aggressive boil lead to lower OG?

I performed both a refractometer and hydrometer reading and came up with the same OG.

Appreciate the help.

The kits are formulated for a 5 gallon postboil.

IE: If you normally collected 6 gallons @ 1.034 (ish) and boiled for an hour, lost a gallon to boil and chilling you would end up with 5 gallons of wort with an OSG of 1.044 if you got around 70% efficiency. Now this would also theorize that you had no trub whatsoever which is not possible so you would then drain 4 (ish) gallons to the fermentor as you will lose around .5-1.5 gallon depending on your exact setup.

With your parameters* you should have seen this:
*( assuming 70% effic, 2 gallon boiloff, 7.25g preboil collection.)
A. Preboil OSG @ 7.25G : 1.030
B. Boiloff of 30% per hour = 2 gallons boiled off in 1 hour
C: If you truly had 5G left in the kettle it should read around 1.040

Being that you are stating you read an OSG of 1.034 thier is something fishy with your measurement/s and I am leaning towards your boiloff rate first before other factors. It is true larger kettles will genrate more of a boiloff rate but 30% is awful high I am going to lean on 21% overall including chilling. This would leave you with 5.75 g wort @ 1.038.

Or your not accounting for trub loss and had a “normal boiloff” rate of overall 17% which would see the 7.25G reduced to 6 G after boiloff and chilling. You then racked only 5 G as the other gallon was locked up in trub/ other etc… This would spell out a perfect 1.035 to match what you saw.

Just throwing out the possibilities per what math we have to work with. Downline try to accurately gauge what your boiloff rate is, preboil collected, postboil( before chilling), postboil (after chilling), amount collected in fermentor, amount left in kettle>>>this is the total volume of wort, trub, hop particulates left in kettle. Then you can gauge what your true preboil should be to receive 5.25G finished wort in fermentor.

IE: I get 5.25G in the fermentor, BUT I have to assume a 6.3G post boil/chill etc…and make my recipes based off of 6.3 instead of 5 G and expect to lose 1 G to trub etc… So All my recipes if based off kits have to be boosted with base grain to get the OSG to agree with what was meant for a 5G postboil. Yah dig?

Here is an example:
NB Helles = 9# pils malt / .5# Carapils = 1.049
(Assuming 70% Effic / 5 G post / Unknown NB preboil for formulation batches / Unknown loss)
My Helles based on same recipe = 10.5# pils / .5# Carapils = 1.049
(79% Effic / 7.5G preboil / 6.3G postboil / 1G loss / 5.25G to fermentor.)

Totally dig. Great explanation. Thanks for taking the time. Will factor that in going forward. Slainte.

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