Winemaking

Winemaking, wine-making, or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid.

During this fermentation, which often takes between one and two weeks, the yeast converts most of the sugars in the grape juice into ethanol (alcohol) and carbon dioxide (which is lost to the atmosphere).

[3] Depending on the quality of grape and the target wine style, some of these steps may be combined or omitted to achieve the particular goals of the winemaker.

Other sparkling wines, such as prosecco, are fermented using force-carbonation — a faster process that involves using machinery to manually add CO2 and create bubbles.

In other cases, the winemaker may choose to hold back some of the sweet grape juice and add it to the wine after the fermentation is done, a technique known in Germany as süssreserve.

Grape quality is affected by variety as well as weather during the growing season, soil minerals and acidity, time of harvest, and pruning method.

A disadvantage of mechanical harvesting is the indiscriminate inclusion of foreign non-grape material in the product, especially leaf stems and leaves, but also, depending on the trellis system and grapevine canopy management, may include moldy grapes, canes, metal debris, rocks and even small animals and bird nests.

In the United States mechanical harvesting is seldom used for premium winemaking because of the indiscriminate picking and increased oxidation of the grape juice.

This can be an effective first line of defense to prevent inferior quality fruit from contaminating a lot or tank of wine.

Depending on the winemaking procedure, this process may be undertaken before crushing with the purpose of lowering the development of tannins and vegetal flavors in the resulting wine.

In traditional and smaller-scale wine making, the harvested grapes are sometimes crushed by trampling them barefoot or by the use of inexpensive small scale crushers.

In some cases, notably with "delicate" red varietals such as Pinot noir or Syrah, all or part of the grapes might be left uncrushed (called "whole berry") to encourage the retention of fruity aromas through partial carbonic maceration.

Red wines are produced by destemming and crushing the grapes into a tank and leaving the skins in contact with the juice throughout the fermentation (maceration).

It is possible to produce white (colorless) wines from red grapes by the fastidious pressing of uncrushed fruit.

This is to avoid any extraction of tannin from either the skins or grapeseeds, as well as maintaining proper juice flow through a matrix of grape clusters rather than loose berries.

In some circumstances winemakers choose to crush white grapes for a short period of skin contact, usually for three to 24 hours.

In the case of rosé wines, the fruit is crushed and the dark skins are left in contact with the juice just long enough to extract the color that the winemaker desires.

During the primary fermentation, the yeast cells feed on the sugars in the must and multiply, producing carbon dioxide gas and alcohol.

[17] Pressed juice is typically lesser in quality due to the release and increase of total phenolic compounds, as well as browning index and the C6-alcohol levels.

As the skins are the source of the tannins, the cap needs to be mixed through the liquid each day, or "punched", which traditionally is done by stomping through the vat.

Cold stabilization is a process used in winemaking to reduce tartrate crystals (generally potassium bitartrate) in wine.

Potassium bitartrate will also precipitate, a process which can be enhanced by cold stabilization to prevent the appearance of (harmless) tartrate crystals after bottling.

The secondary fermentation usually takes place in large stainless steel vessels with a volume of several cubic meters, oak barrels or glass demijohns (also referred to as carboys), depending on the goals of the winemakers.

Sensory tests will also be performed and again in response to these a winemaker may take remedial action such as the addition of a protein to soften the taste of the wine.

Because acetic acid bacteria require oxygen to grow, eliminating any air in wine containers as well as addition of sulfur dioxide (SO2) will limit their growth.

There are several methods available; a typical test involves acidification of a sample with phosphoric acid, distillation of the liberated SO2, and capture by hydrogen peroxide solution.

Besides gelatin, other fining agents for wine are often derived from animal products, such as micronized potassium caseinate (casein is milk protein), egg whites, egg albumin, bone char, bull's blood, isinglass (Sturgeon bladder), PVPP (a synthetic compound), lysozyme, and skim milk powder.

In the making of red wine, sulfur dioxide may be used at high levels (100 mg per liter) prior to ferment to assist in color stabilization.

Microbial stabilization does not imply sterility, i.e. eliminating (removing) or killing (deactivating) of all forms of life and other biological agents.

In the European Union, each member state is required by Article 146 of Regulation 1308/2013 - Establishing a common organisation of the markets in agricultural products and repealing Council Regulations (EEC) No 922/72, (EEC) No 234/79, (EC) No 1037/2001 and (EC) No 1234/2007 - to appoint one or more "competent national authorities" responsible for ensuring compliance with EU rules in the wine sector.