Brix Reading Help

[CTSap4Maple]

I’m using an ATC refractometer and calibrated to 71.5 using olive oil in the 1st photo. Tried cold sap next, but I get a full blue screen reading in 2nd photo after waiting about 30 sec to stabilize (sorry I can’t get the photos upright). The sap is from the bottom of a bucket 1/3 full with the top as a block of frozen sap. Does the sap need to be room temp for a proper reading, or is the frozen sap throwing it off? I’ll try again when I get a full liquid bucket as well. Not sure what I’m doing wrong here. Thanks!

[maple flats]

Did the instructions say to use olive oil? One point is that freezing sap is a poor man's RO. Almost no sugar will be in the ice so you get a much higher reading in the liquid remaining.

[DrTimPerkins]

Yes, EXTRA VIRGIN PURE olive oil can be used to calibrate refractometers. It should be at room temperature (or whatever temperature the refractometer is calibrated to) and allowed to sit for a minute to be sure the refractometer and the oil reach thermal equilibrium. Then it should be EXTREMELY well cleaned with soap/water and rinsed copiously. Any oil left on the refractometer would throw off the reading a good amount or just result in a smear across the entire face (which is what your second photo looks like).

Then you can measure your sap. Since you have ice in the bucket, it'll be concentrated a good bit. If it started at 2 Brix and half the sap in the bucket turned to ice, then the Brix reading would be about 4. Since you've got about 1/3 liquid, you might be at 5 or 6 Brix. After you put the sample on the refractometer plate, close it fairly quickly (to avoid any evaporation) and allow about a minute for the instrument and the sample to come to thermal equilibrium. Then take your reading. If the instrument/sample are NOT at the temperature that the refractometer is calibrated to, and it is NOT automatically temperature compensation (ATC), then you'll have to pull out the chart that came with the refractometer and correct the reading OR only measure when the instrument/sample are at the stated temperature.