If you have the freezer space I say freeze, freeze away! It’s actually somewhat common (for those grape producers who specialize in it like Brehm Vineyards, Vino Superiore, or Wine Grapes Direct) for growers to freeze grapes and ship them to areas of the country where they don’t grow so well naturally. I myself used to send Muscat grapes to a commercial food freezer in Watsonville, California to make Bonny Doon’s famous “Vin de Glaciere” dessert wine in which we pressed semi-frozen grapes to extract concentrated juice.
A difference you might notice when your frozen grapes are thawed for fermentation is that the grapes will be softer and may give up their color and tannin more easily. This is because the grape skin cells, where all the color resides, get pierced by ice crystals. Maceration might be easier and fermentation might in fact be faster because compounds within the grape, including sugar and nutrients, will become available more quickly. This may mean that you will want to especially watch your fermentation temperature and keep things a little cooler if possible. Red ferments tend to get “cranky” when temperatures get above 90 °F (32 °C) because most yeast just won’t tolerate those conditions, especially in the face of increasing ethanol.
One easy hack to try, if you don’t have any kind of jacketed fermentation vessel or cool ambient temperatures, is to toss in frozen “blue ice” packs or frozen water bottles during punch downs. As long as your “blue ice” frozen ice packs or water bottles are completely sealed, they’re a safe, cheap and easy way to cool a heated fermentation down. The larger your must container, the more cooling power you’ll need, however. A couple of frozen 1-gallon (4-L) water jugs should be able to significantly control the temperature of a hot and heavy 30-gallon (114-L) fermenter. Just remember to monitor temperature carefully while cooling because you never want to rapidly chill a fermentation or it will risk sticking. I try to never drop the temperature more than 5 °F (3 °C) in a one-hour period.
Freezing grapes can be an effective way for a home winemaker to take more control of the abundance of the harvest — and to give your cellar and your calendar some much-needed breathing room. Just be aware of the possible changes that the already-burst grape berry skin and pulp cells may bring.