Using vacuum to cool-boil sap

[mantispid]

Has anyone heard of someone doing this? Putting the sap under high vacuum in order to cause the water to boil off at room temperature?

[mapleack]

Yes. The problem is that without high temperature you don't get caramelization for color and maple flavor. A few people use vacuum evaporators to start the process but finish in a flat pan to still get color and flavor. It's a pricey endeavor and more suited to the larger scales of the cane sugar industry.

[nymapleguy607]

I think dominion and Grimm tried it once, problem is you would need to run huge vacuum pumps to keep up with the cfms at high vacuum.

[jrgagne99]

Also, the thermodynamic analysis shows that the energy input is the same, relative to boiling at 1 atm. You may realize efficiency increases due to less wasted heat compared to a traditional evaporator, but building zero-vac boiling equipment is heavy and expensive.

Interestingly, the Brown Company (paper mill) in Berlin NH did some research on this back in the day in their R&D department and (I believe) came to the same conclusions.