Botrytis is the short name for “botrytis cinerea” which is a type of mold that plays a very important role in producing classic sweet wines such as beerenauslese (/beer-in-oush-lays-ǝ/) and trockenbeerenauslese (/trō-ken-beer-in-oush-lays-ǝ/) wines. Botrytis is also commonly known by the name “noble rot” in English or “edelfäule” (/ād-ul-foi-lǝ/) in German. It occurs only when various factors exist in proper harmony. Those include having healthy fully ripe grapes and cold damp mornings contrasted by warm dry afternoons for a length of time. This combination does not occur every year or even in every German wine region (“anbaugebiete”/on-bou-gi-bēt-ǝ/). So when a wine is made from botrytis affected grapes, it is rare. It is a lucky coincidence that riesling is a grape varietal that performs well in climates where botrytis is possible because riesling grapes are susceptible to botrytis.
Botrytis increases the rate at which grapes lose their water content and shrivel. The remaining grape juice (“must”) is therefore very concentrated for wine making. Botrytis also imparts its own unique and special tones which are difficult to describe. Those tones have simply taken on the name of their contributor, “botrytis tones.”