Refractometer reading vs temperature question

[jrm]

I finally ordered two refractometers last week after reading many threads regarding their use. I'll finally learn the sugar content of my sap, which I believe is pretty low based on yields. But, I also bought a high scale one for syrup, as I am only a hobbyist, working with my testing cup can be difficult in stock pot, or smaller, pans in which I am finishing.

Both were supposed to have ATC. The one for syrup, is not marked that way, so I am not sure if it will compensate.

That said, the instructions that came with it indicated the ATC is valid for 20-30c -- that's not high enough for syrup.

i understand I have to compensate for temperature. When using the hydrometer, I keep my temp conversation chart out, so I know what my reading should be when I test.

Two questions... If a refractometer does not have ATC, does that mean I have to manually compensate for the temperature, and if so, do I use the same conversion chart that I use for the hydrometer?

And, secondly, if it does have ATC but the range does not go to a high enough temperature, do I have to compensate there as well?

Thanks for your help in easing my confusion.
Janet

[YBSean]

I just bought a 0-10% brix ATC refractometer for sap and it says the temp range is 10-30 C. I calibrated with distilled water and went to measure sap. Each reading was higher than the previous and when it reached 4% I knew something was wrong. It was a cold day and sap was near freezing and the meter was calibrated inside with room temp distilled water. Today I going to have the meter, distilled water and sap at about the same temp as I think that is important for accurate readings.


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[Polish Wizard]

I hope this isn't considered "hijacking" your thread, but your title perfectly describes my quandary as well.

This is my first year tapping trees, and doing it on a hobby basis on a very modified file cabinet and three 6" deep buffet pans.

My first cook of 40 gallons of sap went relatively well. At first I kept the liquid low in my buffet pans as many folks had instructed and didn't realize all the moisture evaporated from my most concentrated pan.
After the pan actually ended in flames, I regrouped and my process yielded about 1/2 gallon of nearup to finish on a more controllable heat source. Luckily my mishap occurred early in the boil, so not much was lost.

My second cook of 40 gallons went well --- right until the final few minutes when just one more log brought the flame heat too high and all my product boiled over and turned to junk. ---sigh--

My third and most recent cook went very well and I kept the wood fuel and flame very low as I brought the nearup close to 60 Brix.
As I played with a couple sticks at a time, I watched steam rise, but most of the time I couldn't identify an actual "boil" occurring in the pan.

I started to question what I had read about 66 Brix and 7-degrees above boiling water as my targets.
I've proven I can successfully keep the nearup temperature around the boiling temperature of water, which will reduce the water content and eventually reach 66 Brix (sugar content).
So where does 7-degrees above the boiling temperature of water fit into the process?

I currently have about 1-1/2 gallons of nearup in the fridge for final cooking, and hoping the gathering season hasn't reached the end with the recent string of warm weather.

[happy thoughts]

So where does 7-degrees above the boiling temperature of water fit into the process?


That's the temp it will reach if brought to boiling. Water boils at 212F and won't go higher. As the sugar concentration increases, so does the boiling point. The 7+ degrees is equal to the boiling point of syrup at correct density... at least theoretically.

And yes you can reduce water content by keeping the temp below 212. You can reduce a dish of water by evaporation at room temp but you won't increase the boiling point of plain water. You can even make syrup by serial freezing sap and removing the ice. When you've removed enough ice to reach proper density it will boil at 7+ degrees above the boiling point of water And that explains what you discovered. :) Sap isn't plain water.