I have a 750ml bottle of Lustau Almacenista Amontillado Fino which has thrown a very fine, very dark sediment the like of which I have never seen before. If left undisturbed in the glass, it precipitates out quite quickly. The bottle has been open for almost a year and has only an inch or two left in it. Given the ageing and settling time the wine goes through to become Sherry, one would think that anything there was to settle out would be long gone.
What is it?