What happens after fermentation
By Bernard Cannac, Winemaker
After all the excitement of harvest and the fermentations, I enjoy the quiet months of winter. By now, the 2009 reds are aging in barrels and the older vintages are maturing. The 2009 whites have to be prepared before being bottled in the spring and summer.
Like Brian explained in his January 15th blog, the white wines have to be treated with bentonite in order to be protein stable or heat stable. After the fermentation, the wine contains a lot of proteins, some of them coming from the yeasts’ cells. But too many proteins would lead the wine to turn cloudy if it was to be exposed to some heat. If you leave a bottle of white wine, or Rosé or Blush sitting in a car for hours in the summertime, the wine might turn cloudy or hazy. Under heat, proteins tend to form a haze. To prevent this to happen, bentonite is added to the wine. It will attach itself to the proteins in suspension in the wine. The result is a heavy molecule, which will drop down to the bottom of the tank due to its weight. The wines are racked after about one to two weeks after the bentonite addition in order to give it enough time to settle down to the bottom of the tank. Then, we just have to pump the clear wine and discard the sediments left at the bottom of the tank. A gross filtration will take care of any molecules that still might be in suspension.
The other stabilization we have to look after is called cold stability. If you have stored a white, Rosé or Blush wine in the refrigerator to chill it, you might notice that some white or sometimes pink crystals have formed in the bottom of the bottle. No, it is not sugar or sand, and it is not dangerous. If you were to drink some with your wine, the only inconvenience would be that it has a grainy texture and it would feel weird in your palate. One of the most important acids present in grape juice is tartaric acid. Grape juice also naturally contains potassium. When these two compounds react together, they form a crystal called potassium tartrate. This reaction happens faster at colder temperatures. That is why a wine that has not been properly stabilized will produce these crystals when being refrigerated. To avoid this happening in the bottle, we actually make the reaction happen in the tank. There are two ways to induce this: we can chill the tank down to about 28 degrees Fahrenheight and wait for about three weeks or we can add some cream of tartar to the chilled wine. We choose the latter because the stabilization happens faster, in a matter of days instead of weeks. The cream of tartar method is also called “seeding” because the small crystals of cream of tartar induce the formation of tartrates around each “seed” of tartar. When the crystal becomes heavy enough, it drops down to the bottom of the tank. Again, we rack and filter the clear wine and discard the sediments. The red wines get stable after their aging in the barrels, and they should not be chilled, so we do not have to heat and cold stabilize them. Moreover, consumers are more forgiving when they notice sediments in a bottle of red wine.
At this time of the year, we also are busy pruning the vineyard and doing some labeling before getting into bottling some 2007 and 2008 reds and the 2009 whites. I hope it wasn’t too technical and that it answered a couple of questions you might have had. Cheers!