Here is my method & equipment for taking the SG of the wash as it ferments. I believe my method is sound but if someone thinks otherwise please feel free to explain why.
I don't have a Specific Gravity (SG) meter & glass tube so I made a beam balance out of a piece of 3/8" alum tube about 400mm long. A bicycle spoke going through the beam works as a fulcrum. Rails for the spoke to roll on: Short piece of U-channel. The sample bottle is suspended off another piece of spoke that goes through the beam and is 50mm away from the fulcrum. A sliding weight is made from bolts, nuts, washers, etc.
1. Take a small empty bottle about 60~120cc and balance it off with your sliding weight. Where the beam is balanced make a mark, this is "zero".
2. Fill the bottle to the lip (you will always fill it up to here) with water and move your weight to balance the beam again. This is your 1.000.
3. Measure the length from 0 to 1.000, divide that number by 10 and proceed to mark off each increment on your beam. Starting from 0, each mark will correspond to 0.01, 0.02,......1.000, 1.010, 1.020.
To use it just fill the bottle to the lip but this time with your sample and move the weight to balance the beam again. Once balanced, you can read the SG directly off the marks you just made.
To make the tick marks on the tube permanent do a single pass with a pipe cutter. It leaves a mark but won't severe the pipe.
Since this is a ratiometric method it doesn't really matter what the actual weight of the sample is. You are just comparing your sample's weight with water's weight which is what the definition of SG is.
Notes:
It is preferable to use a small-lipped bottle so you get better repeatability of you sample size.
You can use another weight that is fixed to the long end of the beam to offset the bottle's weight. This way your sliding weight will be lighter and you maximize the use of the length of the beam.
Similarly, a beam balance can be made to read EtOH %. I will work that out some other time.
