A fermentation tank is like a good dance club: full of energy, heat and bubbles. Surging around the tank is the usual cast of characters: a mob of bacterial hoi polloi trying to wheedle their way past choosy bouncers and yeasts strutting into the club with only one thing on their minds - sugar. When the juice runs out of sugar, the dancing begins to fade, conversation drifts and the exhausted yeasts pass out. By the time the DJ has packed up his kit, the dormant yeasts, along with other small bits of party debris, are sinking to the bottom of the tank. These passed-out clubbers are called lees (with no disrespect to the Lee family) and they fall into two categories: the gross lees, which United States winemakers refer to as mud, are B-list guests, while the fine lees, comprised primarily of dormant yeast cells, are on the A list. After fermentation, winemakers immediately drain the clear juice from the tank and discard the gross lees lounging on the bottom. Though the juice looks relatively clear, it is laden with lightweight, sleepy yeast cells stirred up by the movement. These small yeast cells play many roles in the development of a wine's character. They infuse it with attractive toasty or biscuit-like flavours and they also have an effect on the wine's texture, making it seem creamier or thicker in the mouth. Lees attract other organisms that help soften the wine and they act as an antioxidant, too, protecting the wine from the harmful effects of too much oxygen exposure. In addition, they provide a protective barrier between the wine and the interior walls of the oak barrels, which might otherwise impart harsh tannins and overt flavours into the wine. Contact with lees is so beneficial, winemakers often stir them up to hasten the process. If wine is maturing in small oak barrels, which have only a narrow opening at the top, the cellar team stimulates the lees with an instrument that looks more suitable for medieval torture: a slim metal pole with a length of chain on the end. The spin technique employed is called lees stirring, or batonnage in French. With aromatic grapes, such as riesling or chenin blanc, lees contact diminishes the wine's fruity character, and is therefore undesirable. With neutral grapes, such as chardonnay, lees are highly attractive as they add vibe and dimension to the wine. This yeastiness is so integral to other wines' beat, they will have 'sur lie' or 'aged sur lie' stamped on the label. Muscadet sur Lie, a crisp, zingy wine from the Loire Valley, is an example. The hottest lees act is in champagne, where winemakers ensure wine has intimate contact with yeast cells by trapping them in the bottle itself, leaving the sludgy yeast layer undisturbed for years and ejecting it immediately before dressing the bottle for release.