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The crystals at the bottom of a bottle of wine are usually a sign that the wine is of good quality. They are more common on red wine where they are stained by the wine and are regarded as part of the sediment. In white wine they remain clear, and some people fear they may be glass.

Not so. They are tartrate crystals formed as part of the aging process. Some wines are more susceptible than others due to the climate where they are made and the grape varieties used. German wines are often affected.

Because many consumers are upset by seeing these crystals in white wine and take them back to the retailer, most mass wine producers process the wine to precipitate and filter out the crystals. This process does, of course, result in a less complex and less interesting wine.

Thus I expect the wine you are referring to is a good quality wine, maybe from a boutique winery, that is developing in the bottle.

As long as the wine is stored properly then it should give you delight when you get around to drink it. However I suggest you do not keep the wine for too long.

Please reassure your friend that the crystals are totally harmless. Don't shake the bottle and pour the wine gently and they will all stay in the bottle.

Thanks to Peter May, host of The Pinotage Club on the Web, for providing this question and answer.