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How to work with percentages

So what’s the best way to figure out how much grain I need if I have the recipe in percentages?
The recipe is 84% 2 row and 4% each of 4 specialty grain.

Thanks

use a program like BeerSmith

That’s just the thing. I did. But you have to basically guess at the starting point. Right now I’ve got 10.6 lbs of 2 row and just under a half a pound for the other 4 specialty grains.
But using 4 other ‘free’ programs, all the amounts are pretty much different given me SG of 1.059-1.071.

THis is just like using 3 different thermometers. You gonna get 3 different readings.
Pick a program and use it. Once you start drifting around your never gonna figure out what went right or what went wrong.

just keep moving the base malt around till you get where you want it and then move the others around to match what you need.

You need a target alcohol or target OG to work it out. There are a couple other variables you need to be familiar with. Like ‘f-factor’ and ‘extract LDK’ for certain grains. Also you need your efficiency.

Let's assume you're shooting for 5.5% alcohol (.13 f-factor). 75% efficiency. 2row is approx 308 extract LDK. And I'll assume your specialty grain is around 275 extract LDK, but I need to know what specialty grain because each grain has its individual extract LDK. And that extract LDK varies from harvest to harvest. I only have the averages..

Here we go. keep in mind you will need to judge your system for final gravity... 

“{} = my assumed values {5.5% abv, 75% efficiency}”

  • = multiplication
    / = division

Start:
determine the batches target extract and OG from the desired ABV

ABV{5.5}/ffactor{.13} = 42.3 degrees gravity

Degree gravity {42.3}/80*100 = 52.89 original gravity {otherwise known as approximately 1.053}

original gravity {52.89} * volume {19 liters which is about 5gallons} = 1004.8 extract LDK

1004.8 Extract LDK/efficiency{75}*100 = 1339.74 target extract

Ingredient #1 = 84% pale malt

1339.74 target extract/100* Percentage {84} = 1125.4 target ingredient extract

1125.4 ingredient extract/ actual ingredient extract {308 (for 2-row)} = 3.65 kg pale malt {8.047 lbs}

Ingredient #2 specialty = 4%

1339.74 target extract/100 * percentage {4} = 53.6 target ingredient extract

53.6 target ingredient extract / actual ingredient extract {275} = .195kg of each specialty {.43 lb}
:End

ingredient #2 is assuming all your specialty grain has the same extract LDK of 275. In reality this is unlikely, and you will have to work out each type of specialty grain to account for their own individual extract LDK

Original gravity {1.053} - final gravity {1.011} * ffactor {.13} = ABV {5.47%}

Keep in mind, every specialty grain has its own ingredient extract LDK. Each percent ABV has its own f-factor. And you have to factor in your personal systems efficiancy.

Sorry about the metric. Is the only way I know how to do it. I don't intend to scare anyone off with the math. It takes some practice to get used to it. a spreadsheet or beersmith is the easier and more practical way to go about it.

‘Edited for clarity’

Fairly accurate way, but not too complicated, is to assume that base grains potentially yield 36 points per lb per gallon of wort and all other grains average out to 30. Then figure your total points needed for your desired volume - say five gallons at 1.060, and it’s 5*60 = 300 points. Then you need brewhouse efficiency, say 75%, so divide 300/.75 and you get 400 points of potential needed from the grain.

With 400 as your target, set up a weighted formula with “Y” as the total weight of grain - Y x (0.84 x 36 + 0.16 x 30) = 400, yielding 11.4 lbs total grain. Then you figure the amount of each grain by using the given percentages.

To check this, I ran a dummy recipe through my spreadsheet with 2-row, Carastan, Chocolate, Melanoidan, and Munich at the given percentages and at 75% efficiency ended up at 11.2 total lbs. So it’s reasonably accurate on this random recipe.

Once you’ve set your malts in beersmith and have set your desired proportions you can adjust a slider to modify your grain volumes to stretch to whatever og you want. The proportions will stay the same.

Using Beersmith 2 and playing around with the OG, I think I’ve got something I can live with.
I appreciate all the help and ideas here. Lots of smart folks around this place.

I agree with the previous comment about different programs. Pick one and stick with it.

I started using a pencil and paper and Shadetree’s method, and I’ve stuck with it.

If you’re just starting to formulate your own recipes, I suggest starting with an established recipe as a baseline and doing some research into the characteristics of various grains, hops, and yeast strains. Then tweak away to achieve the flavor, color, etc. that you are aiming for.

As a Beersmith user, you can download a bunch of recipes–including a lot from NB. Brewing Classic Styles
http://www.amazon.com/Brewing-Classic-Styles-Winning-Recipes/dp/0937381926/ref=sr_1_1?ie=UTF8&qid=1349529750&sr=8-1&keywords=brewing+classic+styles
is a great resource and worth every penny for $12 on Amazon.

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