Homemade RO system makes the sap smell when boiling

[Cryptographic_ICE]

I built a new reverse osmosis system based on this design:
https://sites.google.com/site/mattatuckmadnessmaplesyrup/home/homemade-reverse-osmosis-system

The concentrated sap does not appear to have an foul odor but does have a very slight yellow tint. however when you start boiling the concentrated sap it smells a little bit like seafood or "lobster water". When boiling raw sap if we get foam it resembles bubble bath. The concentrate almost immediately foams up with a very thick foam that is more like whipped cream.

I cant imagine the off smell being normal but maybe it is. We boiled it down to syrup and had a couple of people taste it and they say it seemed fine.

Any Idea what could be going on here? I have done 2 batches with RO and they both came out the same way.

Another issue somewhat related. I was under the impression that concentrating the sap would lighten the color of the syrup. However it still came out very dark the same as a batch we made just before using raw sap. We started at 2-3% and concentrated to about 8%.

[Rangdale]

Did you clean the RO membranes with 5% hydrogen peroxide solution before first use? The first year I made my RO I forgot that step and the first batch of syrup had a funny (probably glycol!) after taste. Once I tasted it I remembered what I had forgotten, cleaned them and all was fine. My design was from the same link. Also, could it just be spoiled sap? I boiled some sketchy looking sap at the end of the year a few years back and it smelled just as you describe. I dumped it and never finished it to syrup but I know others have and it came out ok

[Cryptographic_ICE]

I flushed the system before first use and I flushed the system with 50 gallons of water before the second one. I did not use hydrogen peroxide. After the first run I did consider spoiled sap so I washed all the buckets and evaporator pan. The sap was clear when I started and I put frozen bottles of water in both the raw sap and concentrate to keep it cold.

I did flush it with city water could that be an issue?

[bowhunter]

City water has chlorine in it and that will/could damage the membrane. Not sure if that had anything to do with you odor issue.

[SDdave]

The sap does change a little color on ya when you use this RO. More pronounced change if the sap sat for a day, even with ice blocks in it. The concentrated sap I have noticed does have a more of an earthy smell to it. All in all if the syrup comes out fine a little change in aroma could be overlooked with all the time saved boiling. I have run this system for a few years now, and was thinking on not this year due to the deeper color I've had been getting. But, this year I ran it and got a really nice light amber to amber. I think it's more of speed of processing sap and knowing that syrup color is seasonly and yearly different.

SDdave

[Flat Lander Sugaring]

I have had the same but so far all syrup produced with above issues has never had an off taste or smell after all done. I taste all my syrup right after i filter it if its off by anything it gets put aside all new filters and then wait for next draw.

[Russell Lampron]

I've been boiling concentrate for years and the yellowish tint is normal. The higher you concentrate it to the darker it gets. As for the smell I normally get a woody almost musty smell before the gradient gets close to syrup. When it gets closer to syrup it smells sweet and mapley. With an RO you can and will still make dark syrup. It's just a myth that all you will make is light syrup with an RO. I had to build a bubbler for my evaporator because all I could make was dark syrup.

[Rangdale]

I made over a gallon of syrup (and cleaned them with 30 gallons of fresh water (we have a well) before I realized it had a hint of a funny after taste. Went back and read thru his directions again and realized I had missed the 5% peroxide cleaning step. Did that and it was back to normal.