The book, “Home Winemaking Step by Step” by Iverson has a section on making faux ice wine by concentrating the must by freezing. Since the juice has a lower melting point than water, it will melt first. The freezing was the easy part, I already keep all my must in the freezer. I put a heavy colander over a bucket and inverted a 6qt plastic container of chardonel must into it. After a little while it melted enough for me to remove the plastic container.
The book calls for a brix of 35-40°. The highest mark on my hydrometer is SG 1.16 (which corresponds to about 38°). The melting took 7+ hours, helped at the end by me with a heat gun. I started with 5qt and ended up with just under a gallon. The SG was 1.154 (the heat gun caused me to overshoot my SG goal slightly). I reserved 10% of the must for back sweetening. Then I added yeast nutrient and DAP to the must and went to bed (since it was after midnight by this time). I know that high SG is hard on the yeast, so I used double the yeast nutrient and DAP. The must is at room temp this morning so I’ll be pitching the yeast shortly.