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Mountainbeers 09-24-2009 06:34 PM

Beersmith Efficiency
What is the difference between the batch size, boil size and how do these equate to efficiency or are they not related?

mmb 09-24-2009 06:39 PM

Batch size is amount you're shooting for into the fermentor.

Boil Size is the amount pre-boil, that is, your batch size plus whatever is lost as steam during the boil.

Not really related to efficiency. Efficiency has to do with the amount of sugar you extract from the grain during an All Grain Mash and Lauter.

If you leave too much wort behind in the kettle, that will skew your efficiency numbers, but not really effect efficiency.

Mountainbeers 09-24-2009 06:57 PM

Thanks! Do you know how the IBUs are calculated?

mmb 09-24-2009 07:09 PM

IBU calculations in software are really just approximations based on Alpha Acid (AA%), time in boil, and gravity of the wort.

Here's a pretty lousy wiki article on the IBU scale


Mountainbeers 09-24-2009 07:15 PM

So if my engineering background hasn't failed me am I right in thinking that the larger the boil volume the larger the IBU?

EuBrew 09-24-2009 07:37 PM

Larger boil volume would increase IBU's slightly ONLY if you are shooting for the same batch size. IE if you set your pre-boil volume at 8 gallons for a 5.5 gallon batch you will see a point or 2 higher IBU compared with a 7 gallon pre-boil volume for the same 5.5 size batch. Play with the numbers and you will see it's miniscule at best. The inverse is true if you leave ingredients the same and adjust the BATCH size. The default set volume based on equipment is pretty accurate and accounts for volume lost in your boil based on your equipment.

Mountainbeers 09-24-2009 08:37 PM

OK well I was just wondering why my numbers are so different from Northern Brewers' on this extract kit.


Their IBUs are 26.9 and 1.6 on the hops with ProMash.

With BeerSmith I am getting 14.1 and 1.5.


Amount Item Type % or IBU
6.00 lb Pilsen (2.0 SRM) Extract 92.31 %
0.50 lb Cara-Pils/Dextrine (2.0 SRM) Grain 7.69 %
1.00 oz Hallertauer Tradition [6.00 %] (60 min) Hops 14.1 IBU
0.50 oz Saaz [3.50 %] (10 min) Hops 1.5 IBU
1 Pkgs Trappist High Gravity (Wyeast Labs #3787) Yeast-Wheat

Granted their boil size is 5 gal and mine is 2.5. Should it be that far off?

mmb 09-24-2009 08:41 PM

Yes, because gravity of wort is a variable in the formula. If the batch size is still 5G but your boil volume is only 2.5G you'll need to add water to reach batch size in the fermentor. That means your wort is a higher specific gravity (sugar content) than the full boil. High gravity effects the IBUs utilized.

Mountainbeers 09-25-2009 01:52 AM

I thought so thanks.

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