sits on top of a mechanical crusher-destemmer. Grape clusters are fed into the machine, where they are first crushed, then destemmed. Stems exit at the end, while juice, skins, seeds, and some debris exit the bottom. Crushing is the process when gently squeezing the berries and breaking the skins to start to liberate the contents of the berries. Destemming is the process of removing the grapes from the rachis (the stem which holds the grapes). 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. These can also destem at the same time. However, in larger wineries, a mechanical crusher/destemmer is used. The decision about destemming is different for red and white wine making. Generally when making white wine the fruit is only crushed, the stems are then placed in the press with the berries. The presence of stems in the mix facilitates pressing by allowing juice to flow past flattened skins. These accumulate at the edge of the press. For red winemaking, stems of the grapes are usually removed before fermentation since the stems have a relatively high tannin content; in addition to tannin they can also give the wine a vegetal aroma (due to extraction of
3-isobutyl-2-methoxypyrazine which has an aroma reminiscent of green
bell peppers). On occasion, the winemaker may decide to leave them in if the grapes themselves contain less tannin than desired. This is more acceptable if the stems have 'ripened' and started to turn brown. If increased skin extraction is desired, a winemaker might choose to crush the grapes after destemming. Removal of stems first means no stem tannin can be extracted. In these cases the grapes pass between two rollers which squeeze the grapes enough to separate the skin and pulp, but not so much as to cause excessive shearing or tearing of the skin tissues. 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. Most red wines derive their color from grape skins (the exception being varieties or hybrids of non-vinifera vines which contain juice pigmented with the dark Malvidin 3,5-diglucoside
anthocyanin) and therefore contact between the juice and skins is essential for color extraction. 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 minimizes contact between grape juice and skins (as in the making of
Blanc de noirs sparkling wine, which is derived from Pinot noir, a red vinifera grape). An alternative method to
maceration is hot press or thermovinification. In this practice, winemakers heat up the grapes to extract the juice rather than pressing using a pressure method. The temperature and time ranges depending on the grape variety and preferences of the winemaker. In addition to extracting the juice, this method is sometimes referred to as pre-fermentation maceration as it extracts tannins and pigment from the skins. This wine adjustment was commonly used in New York State's cooler wine regions, such as the
Finger Lakes AVA. Amelioration is also subject to federal regulations. Alcohol of more than 12% can be achieved by using yeast that can withstand high alcohol. Some yeasts can produce 18% alcohol in the wine however extra sugar is added to produce a high alcohol content. During or after the alcoholic fermentation, a secondary, or
malolactic fermentation can also take place, during which specific strains of bacteria (lactobacter) convert
malic acid into the milder
lactic acid. This fermentation is often initiated by inoculation with desired bacteria.
Pressing Pressing is the act of applying pressure to grapes or pomace in order to separate juice or wine from grapes and grape skins. Pressing is not always a necessary act in winemaking; if grapes are crushed there is a considerable amount of juice immediately liberated (called free-run juice) that can be used for vinification. Typically this free-run juice is of a higher quality than the press juice. 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. These compounds are responsible for the herb-like taste perceived in wine with pressed grapes. However, most wineries do use presses in order to increase their production (gallons) per ton, as pressed juice can represent between 15%-30% of the total juice volume from the grape. Presses act by positioning the grape skins or whole grape clusters between a rigid surface and a movable surface and slowly decrease the volume between the two surfaces. Modern presses dictate the duration and pressure at each press cycle, usually ramping from 0
Bar to 2.0 Bar. Sometimes winemakers choose pressures which separate the streams of pressed juice, called making "press cuts". As the pressure increases the amount of tannin extracted from the skins into the juice increases, often rendering the pressed juice excessively tannic or harsh. Because of the location of grape juice constituents in the berry (water and acid are found primarily in the
mesocarp or pulp, whereas tannins are found primarily in the
exocarp, or
skin, and
seeds), pressed juice or wine tends to be lower in acidity with a higher pH than the free-run juice. Before the advent of modern winemaking, most presses were
basket presses made of wood and operated manually. Basket presses are composed of a cylinder of wooden slats on top of a fixed plate, with a moveable plate that can be forced downward (usually by a central ratcheting threaded screw). The press operator would load the grapes or pomace into the wooden cylinder, put the top plate in place and lower it until juice flowed from the wooden slats. As the juice flow decreased, the plate was ratcheted down again. This process continued until the press operator determined that the quality of the pressed juice or wine was below standard, or all liquids had been pressed. Since the early 1990s, modern mechanical basket presses have been revived through higher-end producers seeking to replicate the gentle pressing of the historical basket presses. Because basket presses have a relatively compact design, the press cake offers a relatively longer pathway for the juice to travel before leaving the press. It is believed by advocates of basket presses that this relatively long pathway through the grape or pomace cake serves as a filter to solids that would otherwise affect the quality of the press juice. With red wines, the must is pressed after primary fermentation, which separates the skins and other solid matter from the liquid. With white wine, the liquid is separated from the must before fermentation. With rose, the skins may be kept in contact for a shorter period to give color to the wine, in that case the must may be pressed as well. After a period in which the wine stands or ages, the wine is separated from the dead yeast and any solids that remained (called
lees), and transferred to a new container where any additional fermentation may take place.
Pigeage Pigeage is a
French term for the management of acidity and the secondary pressing of grapes in
fermentation tanks. To make certain types of wine, grapes are put through a crusher and then poured into open fermentation tanks. Once fermentation begins, the grape skins are floated to the surface by carbon dioxide released during the fermentation process. This layer of skins and other solids is known as the cap. 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 ==