After the sticky, 16-hour days that characterize the wine harvest, most winemakers are eager for the quiet of winter in the cellar. Yet despite often losing up to half of their staff as the workload recedes, winter quiet doesn’t mean an end to critical tasks.

These sticky harvest days jumpstart of the wine process: thousands of pounds of grapes and noisy machinery get alcoholic fermentation started, literally turning grapes into wine. Once primary fermentation is complete, the din of fancy machinery disappears and the complexities of cellar work and winemaking commence.

If great grapes are the first ingredient in great wine, most winemakers would agree that attention to detail is the second, and detail-oriented tasks dominate the slow winter season for winemakers and cellar hands. During this time, tiny chemical changes are tediously monitored, and older wines delicately maintained to age beautifully instead of withering to vinegar before landing on a table near you.

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A critical, oft-overlooked task post-fermentation and pre-bottling is “topping up.” Usually performed by a cellar rat scurrying up barrel stacks with a pitcher of wine, topping ensures that barrels stay completely full from one season to the next. Because oak is porous, small amounts of wine (known affectionately as the Angel’s Share) evaporate through the barrel staves, and are replaced by miniscule amounts of air. While this oxygen exchange is responsible for unique wine flavors like vanilla and tobacco, too much air contact–say, because the barrel is left only 3/4 full–dissolves those tasty complexities, quickly overpowering fresh fruit tones of a wine, and leaving drinkers with thin, astringent swill.

Amidst the topping mania, which is a near-constant task in the cellar, winemakers use the calm of dormant vineyards to perfect the blends of both new and old wines to be bottled in the coming year.

Most wines aren’t 100% varietal specific, despite grape-touting labels. In the U.S., for example, a California Cabernet Sauvignon can contain up to 25% non-Cabernet Sauvignon. Though it sounds deceiving, the rule gives winemakers crucial flexibility in crafting the most refreshing wines by allowing them to combine varieties based on vintage variations. For example, underripe-tasting Cabernet Sauvignon could be cured by a small addition of ripe Merlot, or bold, fruity Zin. Wines are also blended to raise or lower alcohol content, which can have a valuable effect on winery taxes, or to make an slightly sweet wine drier, or a dry wine slightly sweet.

Through hours of mixing, tasting, and calculating, winemakers build a blend, and once it’s established, bottling prep takes precedence in the cellar. First wines are “racked” or moved from one vessel to another through huge hoses. Racking separates the clear, bright wine from the sediment that falls naturally to the bottom of the barrel, similar to the sediment found in older or unfiltered wines. The racked wines are then blended in bulk, and allowed to settle (up to 20,000 liters at a time) for several weeks or even months.

As the wine settles before its final journey to bottle, and bright green buds burst from dormant vines, the cellar doldrums disappear and it’s back to busy–often to the delight of the scurrying cellar hands ready to switch from topping old wines to making new ones. Wash, rinse, repeat.