Since I had the reverse osmosis system laid out for assembly, I figured I could take a picture to show how the filters are connected in series. Each filter “cleans” water out of the maple sap — that water is fed into a common output tube where we collect gallons of water (the clean water output lines are removed here so we can see the path maple sap travels, ignoring the clean water). We use this water for rinsing sappy stuff as we collect, filter, and boil the sap … also water we drink, bring out to the chickens and turkeys, give the cat, dump in the washer.

The “dirty stuff” that normally gets discarded? That’s the concentrated sap — each filter’s “dirty stuff” line is connected to the input of the next filter. Which then “cleans” more water from the sap and passes the “dirty stuff” down the line.

The maple “setup” is the reverse of the “drinking water” setup — below — where the “dirty stuff” goes to a common drain line for disposal and the clean water is sent to the input of the next filter for farther cleaning.

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!