Last year we were able to freeze a bit of sap that we recently boiled down into syrup. It took nearly 3 gallons of sap and about 5 hours to make 3/4 of a bottle of syrup.
It was really an easy process. We simply filled a large pot with sap, put it on the stove, set up a fan to blow the moisture away from the cabinetry and let it boil.
The syrup is a little cloudy because we didn't bother to filter it. It has a very rich and creamy maple flavor a bit like maple fudge with a slight chocolaty flavor in there somewhere. The results are wonderful and far better than I had expected.