Another QBrew question

[petts5354]

If I change the Weight of the LME/HME from 3.9 lb (full can) to 1.95 lb (half can) do I also change the hops from 1.00 oz to 0.50 oz (that effects the bitterness by half)

Thanks.

[jpsherman]

If I change the Weight of the LME/HME from 3.9 lb (full can) to 1.95 lb (half can) do I also change the hops from 1.00 oz to 0.50 oz (that effects the bitterness by half)

Thanks.

Nope. When you set the hme in the hops section for 1oz for 5 minutes the program knows the correct ration of IBU/volume.

Only change the amount in the grains section.

[petts5354]

Thanks.

[mashani]

If I change the Weight of the LME/HME from 3.9 lb (full can) to 1.95 lb (half can) do I also change the hops from 1.00 oz to 0.50 oz (that effects the bitterness by half)

Thanks.

Nope. When you set the hme in the hops section for 1oz for 5 minutes the program knows the correct ration of IBU/volume.

Only change the amount in the grains section.

This is incorrect. In the case of HMEs, you do need to adjust the oz of hops proportionately with the amount of HME you use, OR else cut the AA% proportionally if you want.

That is because for an HME the 1oz @5 is some hardcoded value that someone plugged into the database that is mean to represent that entire can of HME's IBU contribution at the intended volume. By only adding half the can, you are only adding half that contribution. It's in effect a "magic number" someone made up to make the IBUs turn out right in the software at the intended volume.

IBUs in an HME are fixed and directly related to the volume of concentrated wort in that can and the volume of intended product. What is in the can at whatever volume it is has some massive number of IBUs at that volume, and when diluted in the INTENDED volume of water will come out to the IBUs that the HME says it is. If you change the volume - be it the volume you add from the can, or the volume of water you dilute it in, you are either increasing or decreasing the IBUs in the final product.

And these IBUs are already "utilized". So utilization formulas do not apply, unlike a hop boil. For example, if you double the amount of water in your wort with an HME you cut your IBUs exactly in half. QBrew may lie about this because it thinks that by lowering your volume you will get better utilization but that is not true when you are talking about an HME. If you use half a can of HME in the intended volume of water then again you are cutting your IBUs in half.

@petts5354, I am absolutely sure I am correct here. And I do not throw out the term "absolutely" very often in brewing.

[jpsherman]

Whoops, sorry about that. What Mashani says makes total sense.