Unlike port, in which the wines are fortified midway through the fermentation, leaving residual sugar that sweetens the wine, dry sherries are fortified after fermentation is completed, leaving little if any residual sugar.

Why fortify? Stay with me.

Unlike the vast majority of wines in the world, sherry is deliberately oxidized. That is, when the newly fermented wine is put in barrels to age, some space is left in the containers for air. This is counter to almost every other winemaking procedure, in which the aim is to protect the wine from oxidation.

If the unfortified wines are fuller bodied, they may be selected to become oloroso sherries. These wines will age under the influence of oxygen, and will develop a robustly savory, meaty character that is completely different from manzanilla. These oxidative sherries are a subject for another occasion.

Finer, more delicate wines will likewise be put in barrels that are not entirely filled, leaving room for air. Almost immediately, in the barrel, a layer of yeast begins to develop on the exposed surface of the wine. This yeast, or flor, imparts the fascinating nutlike, almondy character of dry sherry.

The historical reason for fortifying sherry was to stabilize the wine for shipping. With sherry, the level of fortification indicates what sort of wine it will become. Those intended to age under flor are fortified to about 15 percent alcohol, an environment in which the yeast flourish. Those intended to be olorosos are fortified to somewhere above 17 percent, which kills the flor.

Other wines in the world also age with the benefit of florlike yeast, like certain white wines from the Jura region of France, which are said to be aged under a veil of yeast, or sous voile. These wines exhibit some similarities to sherry, but they come from a different place, are made with different grapes, are not fortified, and they are not aged as sherry is, in a solera.

The solera is almost synonymous with sherry. It is a complex method of blending vintages over time so that newer wines are gradually mixed with older ones to eventually produce a sherry encompassing many different vintages.