# Calculate the gravity of blended worts/beers...



## Mr. No-Tip (27/12/13)

Hi,

Today I did a split double batch - I mash a 50l batch, take 'half' off and hold it at mashout, boil and chill the first, then onto the second. I say 'half' because my 30l urn can't really hold all of the preboil liquid.

I've ended up with 46l between the two batches...Probably pretty close to predictions given the double trub loss, but I'd like to calculate the OG against the recipe just to be sure. Problem is, there are two OGs. I have 28l of 1.052 and 18l of 1.055.

Is there a calculation to help me find the OG of the 46l total? I am sure it can't be too hard to figure out, but its not really my strong point. I imagine lambic blenders must do something like this at the other end of the process...


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## dicko (28/12/13)

Mate, this link may help you, but I would blend an exact small amount of each sample and measure with an hydrometer.

For example take 120mls of each and mix then measure. That should be enough to fill an hydrometer testing tube.


http://mathforum.org/library/drmath/view/60382.html

Cheers


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## Mr. No-Tip (28/12/13)

dicko said:


> Mate, this link may help you, but I would blend an exact small amount of each sample and measure with an hydrometer.
> 
> For example take 120mls of each and mix then measure. That should be enough to fill an hydrometer testing tube.
> 
> ...


Thanks, I'll have a read. I don't know why I didn't think of the blend thing! Of course, they're both covered in the fluffy stuff now...


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## verysupple (29/12/13)

Just calculate the weighted average:

28L + 18L = 46L

28 / 46 * 52 = 31.7

18 / 46 * 55 = 21.5

31.7 + 21.5 = 53.2

The OG of the total should be 1.053


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## Mr. No-Tip (3/1/14)

That's why I dropped down to tertiary maths... Thanks!


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## MHB (3/1/14)

Not just Lambic brewers, all brewers have to solve this type of problem. There is a standard equation and with it you can solve most of the common mixing issues, even working out strike water temperature uses a variation, as does making hot water additions and decoction calculations, the alcohol content and colour of blended beers. Well worth trying to get your head around.

The mixing equation is Aa+Bb = Cc where A+B=C

As with all brewing (and not just brewing) all your units have to be the same, in this case you are working in Litres and SG, the litres part is fine but the SG you have to watch, as the 1.000 part of 1.052 is what is called non unitary, you aren’t really measuring it it’s just there because SG is comparing the density to water. If you get your calculator out and do the same calculation with 1.052 and 1.055... well have fun!
If you were using oP (Plato) you could just shove the oP values in (12.864 and 13.572 oP respectively) straight in, or just forget the 1.000 part and use either 52 or 0.052 as long as you’re consistent you get the same answer.

Putting what you have into the equation we get: -
28*52 + 18*55 = 46*OG (of the mixture)
1456+990=46*OG
2446=46*OG
2446/46=53.174
OG is 1.0532 to the nearest


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