Sugar?

[Botafogo]

If the wine is unfiltered and not cold stabilized then it may do this at room temp. We have a Primitivo that grows a "crystal city" maybe 3/8 of an inch thick on every cork! Does anyone else remember when Deinhard used to take big ads promoting how "wine diamonds" (these same crystals are VERY common in quality German wine) were your "seal of quality"???

Roberto