Manual Calculation Of Extract Potential

[Spencer]

Hi

I've been reading a bit of Palmer about calculating the likely OG of a brew manually, by adding up the the extract potential of each of the grains in the recipe. Not sure I have it right and I'd appreciate some feedback. This is what I have so far;

Sugar, being 100% fermentable, will contribute 46 gravity points. That's like 'a given', and the extract potential of each grain is indexed off that. Once you have your extract potential you then just factor in grain weight, efficiency and batch volume.

To use an example - How many gravity points will 2Kg of BB Galaxy (extract potential of 77.1% less 4.5% moisture) contribute to a 25L batch, assuming 70% efficiency......my calcs go like this;

46 (sugar base) x .726 (ext pot of BBG) x .7 (effic) x 2 (grain wgt) / 25 (batch vol) = 1.87

Does this mean that my 2Kg of BBG adds 18.7 (say 19) points to my OG??

How am I going??? I'd appreciate yor help...

 

[Adamt]

Close but no cigar...

Extract potential is the SG of 1lb of the substance in 1gal of water. Damned imperial system.

BB galaxy has extract potential of 1.037, so 37 points.

so we have:

37 (potential) * 0.7 (mash efficiency) * 2 (kg malt) * 2.2 (lb/kg) / ( 25 (L batch size) * 0.264 (gal/L) )

37*0.7*2*2.2/(25*0.264) = 17.27 gravity points.

 

[Spencer]

Close but no cigar...

too kind i think adamt. i was way off - not even in the same measurement unit universe.

thanks for your help. that is exactly what I was after.

so where do i find a list of extract potentials? I've goog'd a bit and found an article on grains and malt specs but that talks about percentages and stuff. is there a way to calculate EP from the %?

As I'm typing I am thinking I should go back to the 1lb in 1gal thing?

 

[newguy]

I'll point you to a couple of articles on recipe formulation in my club's newsletter, found here. The recipe articles start on page 15. I wrote one and another senior member of our club wrote the other. I'm very technical and number-minded and the other person is pretty much the opposite. They both cover the basics but in different ways. There are some basic extract efficiency numbers in both articles.

 

[Adamt]

Spencer:

Actually the % dry yield multiplied by the extract potential of sugar is close enough.

Your calculations were correct apart from the units though. You multiplied your answer by 10 to get a logical answer, but your answer was out by a conversion factor of 8.3.

I got the extract potential from beersmith... I think on their website somewhere is a free list of malts and their properties.

 

[Kb.]

Easiest way if you want to calculate your grist volumes are:
V= kettle volume in litres
E = total extract in kg
P= degrees plato, (just what i use, similar to Brix, measures amount of extract kg per 1 kg of water, and therefore accounts for change in volume over temp changes)
G = Grist amount in kg
ep = extract potential %
ef = efficiency of brewhouse % (start with an assumption of about 80%, but each brewhouse, and brewer, will be a little different, once you work out what you get in practice vs what you had in theory, you'll be able to work out your brewhouse efficiency).

E= P/100 x (S.G. of P) x V

this gives you the amount of total extract you require to have at a given brew length.

then you

G = E x (grist ration/100) x (100/ep) x (100/ef)

example, 30L brew length at 10.8degrees Plato(equavalent to about 1.0432SG) and 100% pale malt
E= 10.8/100 x 1.0432 x 30L
E= 3.38kg of extract.

G= 3.38 x (100/100) x (100/72.1) x (100/80)
G = 5.86kg


Nb: if you want to use different grains, use the second fomula for each grain, substituing in the ep of each grain, and the grist ratio.

happy brewing

Kb.