When the winemaker has determined that the grapes have reached ideal maturation, usually by sampling and calculating Brix, the grapes can be quickly picked and delivered to the winery. Because temperature is such a huge factor in the quality of white wine, the grapes are often harvested very early in the morning or even at night if the vineyard is lit, either by hand or with machine harvesting. The machines used today have become so gentle that whole bunches can be removed with no premature crushing and this enables large vineyards to be harvested relatively quickly. Certain varieties are too fragile for machine harvesting, and therefore some wineries still prefer hand harvesting for quality control reasons.