That's a good question...I figured I would start two batches at a time....
I have used partial bottles of the WinExpert concentrate before and refrigerated it for a short time to add to the next batch...didn't seem to be a problem....
I looked up the Alexander's Sun Cal Concentrate and it is 68*Brix as is the WinExpert Grape Concnetrates...so the product is about the same strengh...with the SunCal you can choose the grape type you'd like...with the WinExpert product it is an unknown [unpublished] grape, possibly of Canadian source. The cost wouldn't be too much more per batch...
Still mulling this over as I will be needing some sort of grape concentrate to add to my fruit wines this summer.
I used the Welch's frozen Concord concentrate before and found it to be very foxy [grapey] Concord flavor, so wouldn't want to add that to a strawberry wine.
Any other ideas out there????