Alternating raw sap with concentrate

[huxta]

Thinking about doing a small homemade RO. My question is, when boiling, can i swap between raw sap and concentrate in my preheater during the boil? Will it mess up the gradient? I ask because i'm concerned that putting in concentrate after raw, there would be higher sugar % behind lower %. The RO i want to build may not keep up with my evaporator and may need to toss in some raw sap to keep the pans at the correct level.

[maple flats]

As long as you have good head pressure you will be fine. By that I mean that the tank feeding the preheater should be high enough to push the sap/concentrate thru. Generally this would be 2' or more higher than the highest point on the pre heater and the design needs to have good flow thru the pre heater. Be sure to make a way to vent air from the pre heater. The best design seems to enter low and rise uniformly thru the pre heater, then at the high end have a vent straight up with a way to close it (valve) and then down to the evaporator. Some run that vent without a valve, back to the head tank.
Another method where you will not have one follow the other, is to ro from the head tank, and back to the head tank. Then just have the head tank feed the evaporator. That is essentially how mine works. First I concentrate raw sap to about 8%, then , while boiling all this time, I close one valve and open another. Then I'm pulling from the head tank, concentrating even more and going back to the head tank.

[Russell Lampron]

Concentrate all of your sap or enough before you light the evaporator so that you don't have to mix in any raw sap.

[Mel]

Can your RO keep up with the sap run?

[Daveg]

Thinking about doing a small homemade RO. My question is, when boiling, can i swap between raw sap and concentrate in my preheater during the boil? Will it mess up the gradient? I ask because i'm concerned that putting in concentrate after raw, there would be higher sugar % behind lower %. The RO i want to build may not keep up with my evaporator and may need to toss in some raw sap to keep the pans at the correct level.

There are too many variables to know if the disrupted gradient will be permanent during the boil. My 2x6 with separate pans would recover the gradient when I do what you describe because by the time I was
"tossing in raw sap" the batch had already been concentrated more dense than the RO I introduced later.
I think you would have to have a minuscule rig to not be able to re-establish a gradient.

[huxta]

Can your RO keep up with the sap run?
simple answer is no. I will have about 60-70 taps at my cabin so I will be there only about once a week. The ro I want to build is a very small residential 150gpd membranes. Ordering a mason 2x4 xl. I may just run as much on the ro as I can, then when I run out of concentrate, just run raw sap and save the newly made concentrate for the next boil.

[mellondome]

Dont save concentrate.... it is also concentrated bacteria.

I would recirculate the concentrate back to the supply container. Add new sap to the same container as you get it, and pull from the ro when you need more in your head tank.

[maple flats]

Once concentrated the life gets very short. If you need to save, only save raw sap, boil everything you concentrate ASAP. Concentrate degrades very quickly.
However there is an exception. Before I had my RO, I had a 4 day stretch when I had to sell sap, because all my tanks were full. I sold 1150 gal to a producer a few miles from my remote bush. He was preparing for Maple Weekend business and wanted to be sure he had enough concentrate to run all day. This is a guy who gets a huge crowd, he even charges for parking and he gets hundreds of visitors each day. Anyway, after he concentrated the last load I took him on a Tuesday, to 8%, he pumped it to a refrigerated tank and cooled it to 30 degrees, then he saved it until Saturday. He still made medium from it. This would never be possible without the refrigeration that cold.

[huxta]

I was meaning save the concentrate for the next morning. I wouldn't store concentrate any longer than that. I figured with night temps it would be ok. Unless I'm mistaken.

[BreezyHill]

I have had to do the same this past season on several occasions with no problems. You will notice that it will take longer between draw offs on raw or lower sugar than your target concentration level.

My unit is setup to batch and when my head tank gets low I open the valve that feeds it and send enough for usually 30-60 minutes depending on how long til the batch will be done. A few times I pulled from one of the raw sap tanks and ran one passed sap to the evaporator tank (E Tank).

For me there is a sizable wood savings when boiling concentrate sap so I did on several occasions finish a batch late at night and would use that when first firing the evap the next am. At the same time the RO would know also be running to process more sap that was coming in. Some days the RO ran for several hours prior to firing the Evap so that I would not run out of processed sap(PS).

It is a balancing act but if you record your flow rates and your boil rate it doesn't take long to figure when you should start the Evap and have a steady flow of PS.
I do follow the theory of lowering the evap depths in the pans when I shut down so that I have a faster start time and I use hot cools from our outside wood furnace to start the evap. I can usually be boiling well in 10-15 minutes.

You will find that it is like hitting a slow motion button when boiling raw sap after boiling concentrate. I plan to boil only 18% next season and have a chart to calculate out the start times of the evap from when the RO started at different flow levels. My son or wife run the sugar house when I am when I am not there and it is far easier to have thing wrote down in a note book in page protectors than to try and answer questions and get all the facts to solve an issue thru texts. Our sugar house is 250' into NY and cell service sucks!