My experience is consistent. With three membranes in series (low pressure pump feeding high pressure pump), I regularly process to 8% or above at the same rate as with in parallel and recirc. and lots of washing. It is much more efficient in series. Two nights ago I processed over 200-gallons of 1.6% sap to 8% concentrate in just over 12-hrs with one permeate rinse at about 5hrs in (before I went to bed!). The sap was relatively warm given the non-existence of early spring weather here in New England. In my experience, sap temperatures have much more impact on concentration rates than the arrangements of membranes in a small scale system. It also appears that I'm able to keep the syrup grades more "consistent" with the sap (e.g. lighter on average) than when I recirculated and had concentrate with multiple passes. I also feel that when I am able to bottle the syrup within 24-hrs of when it comes out of the tree, it makes a big difference no matter what method you use because there is less time for bacteria growth, impurity buildup and caramelization due to extended time on the fire.
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