Brettanomyces - wine fault so fashionable in the US that it is sometimes just called Brett. This is usually a whole berry fermentation, and no crushing of the fruit is done. Named after French statesman Jean Antoine Chaptal and usually strictly controlled. Often by removing some of the juices. Just after flowering, an excessive proportion of the nascent berries fall off, often because of unsettled cold, wet weather.
Some varieties are more prone than others.
It may also strip out flavor if overdone. American and European parents fruit set - early summer phenomenon which immediately follows flowering. As soon as the vine flowers, a proportion of them are fertilized, or 'set', to become berries, and eventually grapes. The higher the proportion, the bigger the crop is likely to be. In a viticultural context, usually grafting a European fruiting vine on to a rootstock, often chosen for its resistance to phylloxera .