Things are finally returning to normal in the cellar following the harvest. Our last bottling 3 weeks ago freed up many barrels that are now home to 2008 vintage wines. Wines that were inoculated with malolactic culture are finishing up malolactic fermentation (the bacterial conversion of malic acid to lactic acid) that gave me plenty of concern this time last year. That’s because coaxing the bacteria through malolactic fermentation in a high alcohol wine (characteristic of ’07) is one of the most difficult situations that a winemaker will encounter. Alcohol, after all, is a disinfectant that is very good at killing single-celled microorganisms. The 2008 vintage did not produce the exceptionally high alcohol levels seen in ’07.
The next step for the ’08 red wines will be to decant the wine off of its sediment in the barrel (comprised of dead yeast and bacteria cells), homogenize in tank, then decant again back into barrel after at least a day in tank. After this first decanting process, the wines are brilliantly clear, and will require only one or two more of these procedures until the wine is clarified enough for bottling. The sediment in red wines settle very rapidly and completely, due to the relatively high levels of tannin naturally present in all wines (but particularly red wines) and acts as a fining agent*. White wines are more difficult to achieve this level of clarity and thus require filtration.
* (A fining agent is a natural substance, usually proteinaceous, that is added to a wine to facilitate settling. It is not soluble in wine and is removed along with the sediment upon decanting the wine)
This is by no means a slow time for a winemaker. I’m gearing up for another bottling to take place at the end of January. We will bottle the 2008 Seyval Blanc, the 2008 Noblesse Viognier (a new wine), the 2008 Rosé, and the 2006 Port. Preparing white and rosé wines for bottling is an involved process. This is because white and rosé wines are expected to be brilliantly clear and very stable. What do I mean by “stable”? Wines, by nature, are very unstable in some very important respects. For example, wine is a supersaturated solution of potassium bitartrate (you cooks know this as cream of tartar). A supersaturated solution is one that exhibits a fleeting ability to dissolve a particular substance. With very little provocation, that substance will precipitate (become a solid substance) and either make the solution hazy, or settle to the bottom of the container. Thus, even with sterile filtration of a wine, you could potentially find one day that your bottle of wine has developed a sediment of unsightly crystals of potassium bitartrate. To avoid this phenomenom, I will force this reaction at the winery, before bottling. Once this happens, it cannot happen again.
The easiest way to force the reaction is to chill the wine in a tank. This is because potassium bitartrate is less soluble at colder temperatures. This process is called cold stabilization and takes on the order of weeks to precipitate all the potassium bitartrate that can come out of solution at the temperature that you want the wine to be stable at (we want that temperature to be colder that that of your refrigerator), typically 32 F. Red wines do not go through this process. Why? Red wines, because of the extended time typically spent at the winery before bottling, naturally achieve a level of clarity acceptable to most wine drinkers. And, with extended aging, a red wine will develop sediment in the bottle anyway. Besides, with absolutely no sediment in a red wine, the popular ceremony of decanting a wine before serving would become unnecessary.
The other processing white and rosé wines receive before bottling is one called heat stabilization. Like with cold stabilization, a wine that does not undergo this treatment, even with sterile filtration, can develop a precipitate after bottling. This time, a heat unstable wine becomes hazy, instead of forming crystals, and occurs with spending time in a warm or hot environment, typically the trunk of your car in the summer time. The culprit is a heat unstable protein, found naturally in grapes. Unlike cold stabilization, we do not force the reaction at the winery. This would cook the wine and destroy the countless hours we work towards making a fine wine. Instead, we remove the protein before it has a chance to denature with heat. This process involves using a fining agent, one of the few non-proteinaceous fining agents that is derived from a special form of clay, called Bentonite. More formally, it is a hydrated aluminum silicate that exists as infintesimally small plates that carry an electrical charge. This charge attracts wine proteins with an opposite charge, thus they bind and become insoluble, and simply fall to the bottom of the tank. Bentonite has an enormous surface area, about 800 square meters per gram, making it extrememly efficient at removing potentially unsightly wine proteins. Red wines may undergo Bentonite fining, but it is not requisite as with white and rosé wines. Application of this procedure with red wines is at the discretion of the winemaker.
These are just two of the processing treatments that a winemaker will undertake to prepare a white or rosé wine for bottling. They are not glamorous, and aren’t the highlights of any cellar tour, but are critical nonetheless.
-Jason
Vintner of Rappahannock Cellars
