Pressing (wine)

The timing of pressing and the methods used will influence other decisions in the winemaking process. In white wine making, pressing usually happens immediately after harvest and crushing. Here, the biggest decision will be how much pressure to apply and how much pressed juice the winemakers wants in addition to the free-run juice. Some grape varieties, such as Sémillon and Aurore have very "liquidy" pulps that releases juice easily without needing much pressure that could risk tearing the skins. Other varieties, such as Catawba, have much tougher pulps that will require more pressing. In red wine production the timing of when to press is one of the most important decisions in the wine making process since that will be the moment that maceration and phenolic extraction ceases. Some winemakers use the decreasing sugar level (such as brix measurement) scale and press once the wine has reached complete dryness. Often winemakers will use taste to determine if the wine has extracted enough tannins to produce a balanced wine and may press before complete dryness (such as at 3-8 brix). Though removing the skins by pressing often removes some solids that the wine yeast need to complete fermentation and the benefits of pressing early is often balanced by the risk of potential stuck fermentation. The quality of the vintage year and the overall ripeness of the harvested grapes may also play a role since in cool years when the grapes are often harvested under-ripe, the tannins in the grape are often very "green" and harsh. In these years winemakers might press early (such as at 15 brix), a process that the Australians call "short vatting". In warmer years, the tannins may be full ripe or "sweet" and the winemaker may decide to do a period of extended maceration and not press the grapes for as long as a month after fermentation has completed. Usually the pressed juice will require some additional treatment, which can be done separately to the pressed juice alone or to the entire batch of wine if the pressed juice is blended with the free-run. These treatments may include acid adjustments to lower pH, extended settling periods for clarification and additional racking to remove the extra suspended solids and the use of fining agents to remove extra solids or excess tannins. Grape pulp contains a lot of pectins that create colloid coagulation with these solids that will make the wine difficult to stabilize. Some winemakers will use pectolytic enzymes during the maceration process to help break down the cell walls to allow the release of more juice freely. These enzymes are also used with white wines to assist in clarification. The type of pressing used and the amount of suspended solids plays a particular role in filtering decisions as a high amount of suspended solids (particularly natural gums) can clog and damage expensive filters. == History ==

in Grand Junction, Colorado, United States|alt=The lower body of a white man in bermuda pants stomping on red grapes in a wooden knee-haigh vat. The earliest wine press was likely the human foot or hand, crushing and squeezing grapes into a bag or container where the contents would ferment. The pressure applied by these manual means was limited and these early wines were likely pale in color and body. Eventually humans discovered that more juice could be extracted and potentially a better wine could be produced if they developed ways of pressing. It began with the ancient Egyptians who developed a "sack press" made of cloth that was squeezed with the aid of a giant tourniquet. The ancient Greeks and Romans developed large wooden wine presses that utilized large beams, capstans and windlasses to exert pressure on the pomace. There are many church records that showed feudal land tenants were willing to pay a portion of their crop to use a landlord's wine press if it was available. This was likely because added volume of wine (anywhere from 15 to 20%) that pressing could produce versus manual treading was substantial enough to justify the cost. Machine pressing became even more widespread in the 17th and 18th century as the style of winemaking in France and other parts of Europe was shifting towards heartier wines that could age and survive long transport voyages overseas. Winemaking text began recommending the use of mechanical pressings over feet treading in lagars. Even in Bordeaux, which was still using lagars long after Burgundy, Champagne and other French wine regions had adopted the basket press, saw the use of a wine press become more popular after darker, more full bodied wines of Château Haut-Brion produced by Lord Arnaud III de Pontac began receive wide acclaim from English writers. In the 20th century, wine presses advanced from the vertical style pressing of the basket press and ancient wine press to horizontal pressing with pressure either being applied at one or both ends or from the side through use of an airbag or bladder. These new presses were categorized as "batch", which like the basket press had to have the pomace emptied and grapes reloaded, and as "continuous" where a belt or Archimedes' screw would subject the grapes/pomace to increasing pressure from one end of the press to the other with new grapes being added and the pomace being continuously removed. Another advancement was the complete enclosure of the press (sometimes called "tank press") that reduced the exposure of the grape must to air. Some advance presses can even be flushed with nitrogen to create a complete anaerobic environment that can be desired for wine making with white wine grapes. Additionally, many of today's modern presses are computerized, which allows the operator to control exactly how much pressure is being applied to the grape skins and for how many cycles. ==Types of presses==

Wine presses are generally classified into two types—batch and continuous. Batch presses involve pressing a set amount (a "batch") of grapes with the press needing to be emptied of the pomace or "cake" (the leftover skins, seeds and stems) between batches. There are many different styles of batch presses ranging from simple hand-operated basket presses to computerized membrane presses and presses that are "opened" with oxygen able to come into contact with the must or "enclosed" in a tank that allows for anaerobic winemaking. Continuous presses use a helical screw (such as an auger) or belt that transports the grapes from a feed in across a cylindrical screen or between air pressured filled pads that presses the grapes, compacts the cakes and then removes the cake through an output all in one continuous operation. ==Free-run versus pressed juice==

For as long as presses have been used, winemakers have been aware of the different color, body and aroma characteristics of wine made from the "free-run" juice compared to pressed juice. Free-run is the juice that has been extracted through the process of crushing, the natural break down of the grape cell walls during maceration and fermentation and by the own weight of the grape berries as they are loaded on top of each other in a press. Even among press juice there are compositional difference between the various "fractions" of juice produced from initial pressing through subsequent (and usually harsher) pressing. Often winemakers will keep free-run and pressed juice separated for most of the winemaking process including malolactic fermentation and barrel aging with the options to later blend between them to make the most complete, balanced wine, bottle separately under different labels and price tiers or to discard/sell off the pressed fractions to another producer. == Whole-cluster pressing ==

Whole-cluster pressing is where instead of first sending the grapes through a destemmer/crusher the intact grapes are directly pressed still attached to the stems. This is a method that is widely used for white, rosé and sparkling wine production because it usually produces a more delicate, less phenolic and less colored wine. Even some red wine producers (most notably Pinot noir) will use this type of pressing to avoid harsh tannins or "green-ness" that may come from under ripe grapes. This method is different from "stem pressing" where the grapes are crushed and destemmed but portions of the stems are saved and tossed into the wine press to add some phenolics as well as create "channels" for the juice to drain between the skins, which can limit how often the drain screens get clogged. Under the whole-cluster method, the first press fraction is essentially the "free-run" fraction since the grapes berries are only first being broken and releasing juice as the press cycle begins. However, like with the pressing of crushed grapes the composition of the juice changes with each subsequent pressing and these fractions are often kept separate. Unlike crushed grape pressing, where usually the free-run juice is most prized, in whole-cluster pressing the second fraction is often most valued for its balance of phenolic content and aging potential. In Champagne, where whole-cluster pressing in shallow basket press is very common, the tradition of separating the press fractions dates back to Dom Pérignon with guidelines recorded in 1718 by his biographer Canon Godinot. According to Pérignon (Godinot), the free run vin de goutte was considered too delicate and lacking on its own to make fine Champagne and it was sometimes discarded or used for other wines. The first and second pressings (called tailles or cut since the pomace cake was literally cut with ropes, chains or paddles to remove it between pressings) were the most ideal for sparkling wine production. The juice of the third pressing was considerable acceptable but the fourth pressing (called the vin de taille) was rarely used and all other pressings after that (the vins de pressoirs) were considered too harsh and colored to be of any value in Champagne production. ==References==