Crush in the Napa Valley signals the end of the annual grapegrowing season. When the grapes are harvested from the vines, the cellar crew takes over.

At Trefethen Winery, north of Napa on Oak Knoll Avenue, crush started on Sept. 14.

"We have a permanent crew of six people," said winemaker Peter Luthi. "At crush we hire about eight more cellar workers to pair up with our permanent people. There are two operations going on at once. There is the crushing and pressing as well as fermentation taking place in the cellar."

White and red grapes are treated differently in the cellar.

When the white grapes come from the vineyards they are pressed and the juice is pumped into stainless steel tanks which are inoculated with yeast and fermented in the same tank or pumped into oak wine barrels.

Aging in barrels can take from five to seven months, Luthi said.

"Once the yeast has fermented it needs to be stirred and some of wine has to be topped off and replaced with more wine," Luthi said.

When the red grapes are received from the vineyards they are crushed and pumped into a tank. The color of the wine comes from the skins.

The skins and juice are pumped into a stainless tank and fermented.

A pump is hooked to the bottom of the tank and juices are recirculated. The process takes about eight to 10 days.

When fermentation is finished, the wine is drained from the bottom of the tank. All that is left is the skins, which are taken out and pressed for any remaining juice.

The wine is then aged for up to two years in oak barrels.

"Our last day of harvest was Nov. 1, but all of the operations will not be over for another two to three weeks," Luthi said.