Confused about OG and boil off

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jjayzzone

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I'm thinking about jumping into my first all-grain, but i'm confused about something.....

I would be making a five gallon batch, but I hear that you end up with 7-8+ gallons of wort typically after sparging (1 qt water / 1 lb grain + 1/2 gallon sparge water per 1 lb grain).

So, if I were to boil down to 5 gallons, would I end up with the same OG as with the original volume of water, or would the OG be higher....in other words, does only the water boil off, or does some of the content of the wort boil off as well? Would I be better off just increasing the recipe for ten gallons and split that into two five gallon batches so I use all of the wort?

I've only brewed extracts thus far, but i've built my mash tun and want to jump into AG and need some clarification. Hopefully this question makes sense. Thanks!

Jason
 

usurpers26

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(preboil SG * preboil volume) / final volume --> including loss to trub, chiller, etc = OG

So if my preboil SG is 1.045 and I collect 8 gallons of wort and after my boil I have 5.5 gallons left - then my OG would be:
(45*8)/5.5 = 1.065

Any boiling of wort will result in a higher SG as you are concentrating the wort.

I'm thinking about jumping into my first all-grain, but i'm confused about something.....

I would be making a five gallon batch, but I hear that you end up with 7-8+ gallons of wort typically after sparging (1 qt water / 1 lb grain + 1/2 gallon sparge water per 1 lb grain).

So, if I were to boil down to 5 gallons, would I end up with the same OG as with the original volume of water, or would the OG be higher....in other words, does only the water boil off, or does some of the content of the wort boil off as well? Would I be better off just increasing the recipe for ten gallons and split that into two five gallon batches so I use all of the wort?

I've only brewed extracts thus far, but i've built my mash tun and want to jump into AG and need some clarification. Hopefully this question makes sense. Thanks!

Jason
 

Saccharomyces

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Suppose I have the following recipe :):

10# 2-row

Let's assume the max potential yield of this 2-row is 37 points/lb/gallon (typically it is around that). This recipe is said to yield 10*37 = 370 potential points.

Now, you said 5.0 gallons so that means if my mash/lauter efficiency to kettle was 100%, when all is said and done I would have a 1.074 wort (370 points / 5.0 gallons). Pre-boil if I collected 10 gallons I would have 1.037 wort because the sugars are diluted with twice as much water. The gravity is just the concentration of sugar. You don't boiloff sugar, you boiloff water.

Some more realistic numbers... if your mash/lauter efficiency is 65%, which is typical for a first timer using a LHBS mill - you collect 7 gallons pre-boil, and boil down to 5.5 gallons, I would expect you would have (370 / 7) * 0.65 = 1.034 pre-boil and (370 / 5.5) * 0.65 = 1.044 wort after the boil. So, 10# of grain should yield a low gravity session beer which will ferment out to 4 - 4.5% alcohol or so. This is assuming a typical boiloff rate of 12-14% with a standard 8-10 gallon turkey fryer setup at a good rolling boil for one hour.
 
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