A few home winemakers plant their own vineyards and produce estate wines simply because high quality grapes are so difficult to buy. Warm Fruit Oxidation and other changes start to occur when the grapes are picked, and fruit should be loaded, transported and processed quickly to minimize these changes. However, exceptions to the above rule are sometimes necessary when grapes are picked late in the afternoon on a hot day. Under these condition, the grapes may be very warm. Hot fermentations are difficult at best, so in this situation, letting the fruit sit overnight and cool down may be the lesser of two evils.
Larger wineries cool warm fruit with large refrigeration systems.
Small wineries and home winemakers try to avoid warm fruit. On harvest day, small producers get to the vineyard early while the grapes are cold. Then they load, transport and process the grapes quickly. Unfortunately, home winemakers seldom have much control over when or how the grapes are picked. Large vineyards must cater to local wineries, and grapes going to a winery are usually the first to be picked and loaded.