Noob AG question

[trevorc13]

I've been brewing pretty obsessively for the last year but have only done two ag batches. I am still confused over how the grain bill can influence the abv of a beer. I know that a larger grain bill, say 20 lbs would be a bigger beer than a 10 lbs beer, but what I'm confused on is the fact that the same ratio of water is usually used (say 1.25 qts per lb). Shouldn't this make the same gravity beer no matter how much grain you use, as long as it's the same ratio of grains? You'd just have more wort. The only thing I can think of is that you'd have a larger batch of wort to boil down to your 5 gallons, condensing the beer. That could be a very long boil. Is this the case or can you just use less sparge water and always yield 6.5 gallons pre boil. If that's the case, for some really big beers I'd use about 8 gallon of strike water, would I not even worry about the sparge? Thanks for the input.

 

[rtt121]

1.25 qts to pounds is your mash water.

You sort of have a lot of questions there I hope this answer helps.

Lets keep everything constant except grain bill.

5 Gallons with 10 pounds of grain and 1.25 gts to pounds of strike water gives 3.125Gallons of strike water

10 pounds has a grain absorbtion of about 1.25 gallons
3.125-1.25 = 1.875 Gallons of first runnings


5 Gallons with 20 pounds of grain gives 6.25 gallons of strike water.
20 pounds has a grain absorbtion of about 2.5 gallons
6.25 - 2.5 = 3.75 Gallons of first runnings

To this point the 10 pounds mash and the 20 pounds mash should have the same SG.

The difference from here is the sparge water/top up water. Lets say we need a preboil of 6 gallons. We will add 4.125 gallons of water to the 10 pounder to reach 6. We will add 2.25 gallons of to the 20 pounder to reach 6.

So its about dilution. The sparge/top up water is diluting the disolved sugars. The more diluting water, the less sugars in the final volume.

Hope this helps

 

[trevorc13]

Well said. That makes a lot more sense to me. The amount of sparge water changes to dilute the strike water, giving a different amount of sugars, with the same boil volume. Thanks for the quick reply.

 

[passedpawn]

That is only the mash-in ratio. The difference in sugar concentration (and ABV) is because the big beer requires a lot less sparging, which lowers the concentration.

Let's say you've got 10# grain. So, you mash in with 12.5 quarts (3 gallons) of water. At the end of the mash, you open your valve and you only get about half of that (the rest is stuck in the grains). So, you start sparging. The runnings from the sparging are successively lower in sugar content. The more you sparge (in order to get to your boil volume of, say, 6gallons), the lower the sugar concentration becomes.

If you made a big beer, you will have twice the amount of sweet wort from the initial runnings. So, you'll sparge a lot less. Consequently, the sugar concentration will remain high.

 

[rtt121]

You'd just have more wort. The only thing I can think of is that you'd have a larger batch of wort to boil down to your 5 gallons, condensing the beer. That could be a very long boil. Is this the case or can you just use less sparge water and always yield 6.5 gallons pre boil. If that's the case, for some really big beers I'd use about 8 gallon of strike water, would I not even worry about the sparge? Thanks for the input.

I think with what you said above, you are assuming the same ratio of sparge water.

If you were to do that you would be correct, you would have to boil the bigger batch down to 5 gallons. Instead of starting from 6. You would be starting from 8.25 preboil (check my math?). In this case you would have the same SG for both batches and you would be "condensing less" with the 10 pounder than you would in the 20.

As for really big beers. The first runnings are always going to be the highest concentration of sugars. Often times brewers will run there first runnings off and make a big beer. Then sparge and ferment those runnings seperate for a smaller beer. This is called partigyle.

If you did not want to make a smaller beer, then you could acheive the same OG using less grains *if* you sparge. But, if the time spent sparging isnt worth the extra weight in grain for a no sparge... go for it!

 

[rtt121]

Well said. That makes a lot more sense to me. The amount of sparge water changes to dilute the strike water, giving a different amount of sugars, with the same boil volume. Thanks for the quick reply.

You got it! Your welcome