Beertools Issue

[johnnymac]

Guys, do you use beertools for your recipes? I have been using it since day one and have come across something that really causes me to miss my numbers. It has to do with volume.

Simply put, if you boil off 1 gallon per hour in your brewpot, your numbers will be very different than what Beertools estimates depending upon your batch size. Here's what I mean.

If you are doing a single batch. Your preboil would be 6 gallons and after a one hour boil your volume would be 5 due to evaporation. This represents 17% evaporation rate.

If you are doing a double batch. Your preboil would be 12 gallons and after a one hour boil your volume would be 11 gallons. This represents a 9% evaporation rate.

17% vs. 9%

This is where I have a problem with beertools. It doesn't calculate this difference. If you enter a 5 gallon recipe and double your grain bill and double your volume, it gives you the exact same OG for both batches when in reality, the 10 gallon batch should have a 8% lower OG because you haven't concentrated it as much as you would a 5 gallon batch...

Also, I downloaded the BeertoolsPro Trial. I imported one of my recipes from the online version. When it imported my recipe, it automatically defaulted the boil time to 1.5 hours. When I backed the boil time down to 1 hour, it reduced my OG accordingly. This bothers me because it means that the online version defaults to 1.5 hour boils..... and there doesn't seem to be a way to change it.

Any ideas?

[siwelwerd]

I believe this is because evaporation depends only on the surface area, and not on the total volume (except in limiting cases maybe). So "Gallons per hour" is the right way to think about it, rather than a percentage of batch size.

In your example, you should not double the pre-boil volume. You should simply add the expected evaporation (in this case 1 gallon). So at the end of the boil, you have twice as many fermentables in exactly twice as much water, for the exact same OG.

[johnnymac]

I agree with you Pre-Boil. Same amount of fermentables, same amount of water.

Not true after a boil. Same amount of fermentables.....less water = higher OG. Small batch loses 17% of its water by volume. Large Batch loses 9% of its water by volume.

You mentioned do not double pre-boil volume. Here is another example:

If you are doing a single batch. Your preboil would be 6 gallons and after a one hour boil your volume would be 5 due to evaporation. This represents 17% evaporation rate.

If you are doing a double batch. Your preboil would be 11 gallons and after a one hour boil your volume would be 10 gallons. This represents a 10% evaporation rate. Thus, your single batch would be 7% higher OG.

When I do a double batch, I can usually expect to gain about 6 points on the boil due to evaporation. -Say from 1.050 to 1.056ish

When I do a single batch, I gain considerably more. 1.050 to 1.062ish because the wort is more concentrated.

[siwelwerd]

You missed my point. Your preboil volumes should be calculated to give you the proper post-boil volume. You know you lose 1 gallon in a 60 minute boil (for example). So for your 5 gallon batch, you have a 6 gallon preboil. For a 10 gallon batch, you want 11 gallons preboil. When you are done with the boil, you then have 5 and 10 gallons respectively. In this scenario, doubling the grain gives you the same OG (assuming no efficiency change based on batch size).

I should add that, if you are using different kettles for the different batch sizes, you may have different boil-off rates. But generally it is a function of surface area.

[johnnymac]

I think I'm thinking about this too much.....

In my second example you'd have a higher preboil number on the larger batch so I guess it would work out to be the same. Thanks for your help.

[siwelwerd]

In my second example you'd have a higher preboil number on the larger batch so I guess it would work out to be the same.

You got it. But we really only care about the pre-boil number in terms of using it to predict the post-boil number (okay, it does affect hop utilization too, but the software takes care of that for you).

I find it helps to figure out what you want to end up with and work backwards from there--on my system, I know I need 6.3 gallons in the kettle post boil, so I add the boil-off amount to that (say, 1.5 gallons). So I know I must have 7.8 gallons pre-boil. Now I compute that to end up with 6.3 gallons of 1.050 wort requires a pre-boil gravity of 1.059, and can get the appropriate grain amount based on my efficiency to hit this.

Hope that makes sense, I'm happy to clarify if not.

[Kerth]

Your pre-boil gravity would be lower not higher. In the last example of 1.050 a pre-boil would be 1.040 (1.0404)

[siwelwerd]

Thanks Kerth, you're absolutely right. I multiplied instead of divided. This is why I let ProMash handle this for me, I just tell it how much beer I want.

[Kerth]

I do all my recipes using a calculator.