About Winemaking


by Lum Eisenman

High quality wines are produced by a multiple step process, and for red wines, the process often lasts a year or more. The basic winemaking steps are (1) grape processing, (2) fermentation, (3) clarification, (4) stabilization, (5) bulk ageing and (6) bottling. Although these steps may overlap in time, each step makes a specific contribution to the overall qualityof the finished a wine. Some beginning winemakers think of winemaking as a much shorter process because they are unaware of how the steps of stabilization, ageing and bottling influence wine quality. How each of the major winemaking steps affect wine quality is briefly discussed below.

Grape Processing

After the grapes are harvested and transported to the winery, the fruit is crushed, de-stemmed, pressed, etc. Home winemakers often think of crushing and pressing as “real winemaking.” However, these are only mechanical processes. Machines are used to do the crushing and pressing. If the equipment is working properly and if it is used correctly, these basic mechanical operations do not affect the finished wine. How the grapes are dumped into the crusher hopper should not affect wine quality significantly. By far the most important wine quality factor associated with grape processing is deciding when to harvest the grapes.


Before fermentation, the must or juice is tested and any necessary adjustments are made. When white or blush wines are made, the juice is cooled and allowed to settle overnight. The clear juice is then racked off the sediment before being inoculated with yeast. Red wines are usually inoculated with yeast shortly after being crushed. Winemakers also inoculate juice or must with bacteria when malolactic fermentation is desired. Throughout the fermentation process, the winemaker carefully monitors the progress of the fermentation. Sugar readings are taken with a Brix hydrometer at least once each day, and the fermentation is smelled and tasted often. One of the more important factors affecting white wine quality is fermentation temperature, and high quality white and blush table wines are fermented at temperatures ranging from 45 to 60 degrees. Some important factors affecting red wine quality during fermentation are skin contact time and the way the cap is manipulated.


Little sulfur dioxide remains when fermentation is complete, so a post fermentation dose of sulfur dioxide is added to protect the wine from oxidation and microbial spoilage. Dose levels of 50 milligrams of sulfur dioxide per liter of wine are typically used, and this sulfur dioxide addition can be a significant aid in clarifying some wines. After being racked two or three times, practically all red wines become clear without fining or filtration. Consequently, red wines seldom need any special clarification treatment. Red wines are often fined with gelatin or egg whites, but these protein fining materials are used primarily to remove tannin and astringency from red wines. White wines are more difficult to clarify, and practically all white and blush wines require specific clarification steps including fining and filtration. Several fining materials are used for clarifying white wines, but Sparkolloid is the fining material of choice. Many white and blush wines will not be completely clear after fining, and some kind of filtration is often needed to completely clarify these wines. Quality issues here involve attaining adequate clarity without stripping the wine of desirable taste and odor characteristics.


All white wines should be “hot” stabilized by removing excess protein from the wine. If the protein is not removed before the wine is bottled, the protein may precipitate later and produce unsightly sediments in the bottle. The term “hot” stabilization is used because warm storage conditions speed up the protein precipitation process. Excess protein is removed from white and blush wines by fining with bentonite. White and blush wines are chilled before serving, and sometimes the cold temperature causes tartrate crystals to precipitate out of the wine. Consumers do not like to see crystals or hazes in their wine, so all commercial white and blush wines are given a “cold” stabilization treatment sometime before bottling. Cold stability is achieved by cooling the wine to about 28 degrees for a week or two. Red wines also contain tartrate. However, red wines are seldom chilled before serving, and tartrate crystals are not so easily seen in dark colored wine. Home winemakers and a few small commercial wineries do not bother with cold stabilizing their red wines. Wines can be damaged by excessive or careless handling, so winemakers often combine winemaking treatments. A standard practice for hot and cold stabilizing white and blush wine is as follows. (1) After the new wine is racked off the gross lees, bentonite is added to remove excess protein. (2) Then the wine is chilled to about 28 degrees for a week to precipitate out the tartrate. (3) The cold wine is further clarified by being filtered into a clean tank. Then the clear, stable wine is allowed to warm to ambient temperature. Stabilization strongly influences wine quality, and sometimes good long term bottle stability is difficult to obtain without over processing the wine by excessively handling, fining or filtering. In addition, cold stabilization must be carefully done because cold wine can be oxidized easily.

Bulk Ageing

Bulk ageing is a very important part of producing high quality wines, and ageing often overlaps the stabilization, clarification. High quality red wines are aged in barrels for one to three years, and these wines are often aged in the bottle for several additional years. Ageing can make the difference between a good wine and a superb wine. Full-bodied white wines like Chardonnay or Sauvignon Blanc are often aged for a year or so before they are bottled On the other hand, the charm and appeal of many fruity white and blush wines are due to characteristics associated with fresh grapes. These fruity characteristics diminish as wine ages, so fruity wines are usually bottled and consumed a few months after harvest. Two important quality factors are associated with wine ageing. First, a clean, cool and quiet environment must be maintained to age wine effectively, and the wine must be protected from excessive oxidation. Another quality factor involves determining when the optimum ageing has taken place, and the optimum ageing time can be difficult to determine. No suitable laboratory tests exist, so the winemaker’s experience must be relied upon. Deciding just when the wine should be bottled can affect wine quality markedly.


Only clear, stable and properly aged wine should be bottled. Often, small additions of citric acid, sulfur dioxide, metabisulfiteā€š potassium-sorbate, (sugar) and other materials are made to wines just before bottling. However, care is required here because large additions of tartaric acid or significant blending can make wine unstable, and the stabilization steps may need to be repeated. Getting wine into the bottle without contamination or excessive oxidation is always an important quality factor, and home winemakers spoil large quantities of white and blush wine each year because of excessive oxidation. Oxidation can be reduced by raising the free sulfur dioxide content of the wine to 30 or 40 mg/l just before bottling. In addition, the bottles should be filled from the bottom up with a minimum of splashing and foam.


High quality wines are produced by a lengthy process. Many steps are involved, and each step makes specific contributions to the quality of the finished wine. Clarification, stabilization and ageing make significant contributions to wine quality, but the most important wine quality factor is the quality of the starting grapes.