Well, I received the other hydrometer just in time for all hell to break loose at work, and I had to work 7 days per week, and up to 12 hours per day for several weeks in order to get the problems sorted out. I did take some more readings with the triple scale hydrometer during that time, and have since taken some readings with a more accurate hydrometer. Now the work problems are behind me, I hope to get on with investigating things on a regular basis.
First, the equipment I am using:
- Refractometer: RHB-32ATC - reports readings in 0.25 Brix increments
- Hydrometers: 1 * 1.000 - 1.050, and 1 * 1.050 - 1.100 graduated in 0.0005 increments
- Eyesight: Not too bad if I use a magnifying visor to read the hydrometers
Next, what I have learned and changed since mid November:
- I used to used 3 decimal places for the resolution of hydrometer readings. I now realize that this can introduce significant errors when calculating the Brix Correction Factor, so I have increased it to 5 decimal places.
- Hydrometers are difficult to use. First, you have to apply a calibration adjustment using arithmetic, then you have to apply temperature correction using a calculator. I wrote a simple calculator program where I can select the hydrometer, and enter the observed reading and temperature, and it reports the correct calibrated and temperature adjusted gravity for the selected hydrometer
What I have done.
So far, I have taken pre and post boil readings of 6 * 5 gallon brews, and 2 small scale experimental brews. In each case, I measured the Brix and S.G. both pre and post boil, and used these measurements to calculate a Brix Correction Factor.
Three of the 5g batches and both of the experimental batches were measured with a triple scale hydrometer with a resolution of 0.002, and truncating gravity measurements to 3 decimal places. These were not very accurate. The remaining 3 5g batches were measured with the accurate hydrometers, and gravity measurements truncated to 5 decimal places. These should be more accurate.
What I have yet to do.
I want to do a number of small experimental batches using either Maris Otter, Pilsner, or US 2 row at various mash temperatures and thicknesses, and also test some specialty malts in isolation, and then in combination with some base malts to see what effect the malts and mashing conditions have on the Brix Correction Factor and the % attenuation. Before I do this, I need to establish a procedure that allows me to produce small batches with a reasonable pre-boil and post-boil gravities. (The previous attempt to do this started with a gravity of 1.0155 and ended with a gravity of 1.060 which is not very typical.)
Here are the results that I have come up with so far.
5 gallon batches using 95% Maris Otter and 5% Muntons Crystal 55. Each batch mashed for 90 minutes at 150F. The measurements were taken with the triple scale hydrometer and gravity corrections were truncated to 3 decimal places.
Code:
Pre-boil
Brix 11.5 11.5 11.5
S.G. 1.043 1.044 1.042
BCF 1.0733 1.0497 1.0979
Post-boil
Brix 14.6 14.75 14.6
S.G. 1.057 1.056 1.056
BCF 1.0399 1.0684 1.0576
The next 3 batches used the accurate hydrometers, and 5 decimal places for the SG's. All 3 were mashed at 1 qt / lb. The first was mashed for 90 minutes at 150F, and contained 95% M.O, and 5% Muntons Crystal 55.
The second brew was mashed at 148F for 90 minutes, and contained 93.7% M.O. and 6.3% Muntons Crystal 55.
The third brew was mashed at 148F for 90 minutes, and contained 86.8% M.O. 5.7% Muntons Crystal 55, and 7.5% Flaked Barley.
Code:
Pre-boil
Brix 11.4 9.5 13.5
S.G. 1.04368 1.03637 1.05226
BCF 1.0480 1.0425 1.0446
Post-boil
Brix 14.125 11.5 16.75
S.G. 1.05475 1.04618 1.06732
BCF 1.0454 1.0020 1.0189
Conclusions:
- The pre-boil correction factors with the more accurate hydrometers and using 5 decimal places for the S.G. seem to be pretty consistent. Those measured with the triple scale hydrometer and 3 decimal places varied widely.
- Reducing the mash temp from 150F to 148F appears to substantially reduce the post-boil correction factor
- The post-boil correction factor appears to be lower than the pre-boil factor (except for in one case measured with inaccurate equipment, and truncated hydrometer readings)
Over the weekend, I hope to do a mini-batch using just M.O. at 1 qt per lb at about 148 - 150F (I don't have the mash temp calibration worked out yet for my 1 liter vacuum flask so the mash temp could be a bit off).
Sometime during next week, I hope to do a small test using just crystal malt.
-a.
