We’ve been running the reverse osmosis system at about 95 PSI and concentrating the sap from around 2 percent to 7-8 percent. That’s a lot of water being pulled out (and the water tests at 0 … so we’re not wasting a statistically significant amount of sugar in the filtering process).

We collected nine gallons of sap with SG of 1.009 = 2.3 Brix

We ran all of the sap through the reverse osmosis system at 60psi and had sap with SG 1.011 = 2.8 Brix

We ran the concentrated sap through the reverse osmosis system a second time, this time at 80psi and had sap with SG 1.022 = 5.6 Brix.

The “pure water” output SG was about 1.003 — we re-ran this through the RO as well.

At the end of the day, we have about 4 gallons of sap at 5.6% sugar, another gallon from the “pure water” run that’s a lower SG, and four gallons of water that’s removed.

Notes for the future:

• We want to see what a single pass at higher pressure does — is it multiple passes that farther concentrated the sap or the higher pressure?
• We took SG readings and converted to brix using an online converter. Next time, we should just take the readings in Brix 🙂
• We might need a different refractometer to get accurate readings near 1 … not sure how accurate our tool is at the low end of the range.

We’ve got all the bits and pieces to assemble our maple reverse osmosis system — four 150 gallon per day filters, a pre-filter, pump, pressure gauge, and a valve to control how much pressure we allow to build up in the system. Plus some tubing and connectors, of course!