It appears the Brew Session tool conversion efficiency calculator does not make a correction for grain moisture content (typically about 4%.) When I calculate for 12 lbs 2-row (1.037 potential, dry basis), 4% grain moisture content, 8 gal strike volume, and 100% conversion efficiency I get a wort SG of 1.0488. If I then set the grain moisture content to 0%, force the wort SG to 1.0488 and goal seek to determine the conversion efficiency, I get 95.4%! That's the same as BF calculates, so BF is not correcting for grain moisture content. This results in BF underestimating conversion efficiency.

Brew on

Aha, so my conversion efficiency may actually be ~4-5% higher than I've been thinking, thanks to Brewer's Friend's miscalculations. It looks like I need to switch calculators.

Now to figure out what the wort correction factor actually is on my refractometer

For reference, it's a Milwaukee MA871.

I bought a 0-12 brix hydrometer to use for this purpose, and found that in RO water at 20C, it reads 0.5 brix. I then combined 20g of table sugar with 180g of RO water to make a 10 brix solution. In this solution my hydrometer read 10.2 brix.

Given these two data points, I worked out the following equation to convert my hydrometer measurement to its true value:

corrected value = (measured brix - 0.5) / 0.97

I brewed twice over the weekend, and took three wort measurements with both my hydrometer and refractometer. Note: my refractometer reads 0 on RO water.

Hydrometer 5.3 brix @ 22.8C

Temperature adjustment: 5.4

Corrected value = 5.05

Refractometer 5.3 brix @ 20.7C

Wort Correction Factor: 1.05

Hydrometer 7.8 brix @ 23.9C.

Temperature adjustment: 7.95

Corrected value = 7.68

Refractometer 7.8 brix @ 20.6C

Wort Correction Factor: 1.02

Hydrometer 10.2 brix @ 22.8C

Temperature adjustment: 10.3

Corrected value = 10.1

Refractometer 10.1 brix @ 20.8C

Wort Correction Factor: 1.0

So either my sucrose solution wasn't a true 10 brix solution, or the wort correction factor of my refractometer decreases with higher sugar concentrations. I'm confident that my measurements for making the solution were correct, but it's possible that my table sugar wasn't 100% sucrose.

Note: I used the Brewer's Friend hydrometer temperature adjustment calculator. Maybe not the most reliable source given the earlier findings.

Note note: I need to double check the water temperature for the 0 reading on my hydrometer.