Yes, there is a temperature at which you can hold concentrate. Dr Tim posted a chart on that someplace. It all depends on the sugar%. It doesn't need to freeze 1-2 degrees above works well. A friend of mine bought 1150 gal of my sap over a 4 day period, while my wife kept boiling what we had in our sugarhouse tanks (the last year before we had our RO). Those 4 days, were Friday-Monday, he ran it thru his RO each day and sent it to a working tank that cooled it to 30F. The following Sat and Sunday was Open house weekend. He made some nice medium amber with it. He kept half, I got the other half (a 30 gal barrel full).
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.