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Basic efficiency question

So I completed my first all-grain batch yesterday and my first attempt at calculating eff. produced this question:

Do I use the 6 gallons of pre-boil wort in my initial calculation or the 5 gallons post-boil?

I ask this because I have to do split boils and didn’t take a gravity reading until everything was cooled down and combined into the primary (before pitching). However, after sparging I actually had 6 gallons of liquid and if I’m calculating correctly my eff. would be terrible when using 5.

My calcs are:

OG 1.034 (34) * 6 gal = 204 pts

204 / 8 lbs pale malt = 25.5 ppg

25.5 / 36 (max eff. for pale malt?) = 70.83%

but at 5 gallons it goes down to 59.03%

you use the SG reading take for that particular amount. so, if the 1.034 was the reading for the 5 gallons post boil, then you’d use 5 gallons. if 1.034 was the reading for the preboil, then you’d use 6.

cheers.

[quote=“StormyBrew”]you use the SG reading take for that particular amount. so, if the 1.034 was the reading for the 5 gallons post boil, then you’d use 5 gallons. if 1.034 was the reading for the preboil, then you’d use 6.

cheers.[/quote]

Just to clarify for the OP in case it isn’t obvious: you would have to use pre-boil data (volume and SG) to calculate the efficiency of your mash+lauter process, which is what most people are referring to when discussing efficiency.

A pre-boil SG of 1.034 and a volume of 6 gallons is the same as a post-boil SG of 1.041 at a volume of five gallons.

Also, I use 37 gravity points per gallon per pound of malt, (not 34 like you used)

Using your brew, I would calculate like this:

8 lbs malt x 37 points per gallon/pound = 296 points (theoretical gravity yield)

6 gallons x 1.034 (34) = 204 points (actual gravity yield)

204 (actual) / 296 (theoretical) = 69% efficiency

Or if you use 34 points per gallon (34 x 8 = 272):

204 (actual) / 272 (theoretical) = 75% efficiency

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