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Carl Hudson
May 23, 2018 | Wine "Fun" Facts | Carl Hudson

Grape Skins Key to Red Wines

Making red wines differs in several ways from white wines, the most important difference being skin contact with the grape juice.  The grape comprises 3 basic parts, the skin, the pulp, and the seeds.  For most grapes, all color is in the skin as the pulp containing most of the water and sugar is essentially colorless.  So, if you want to make a red wine from red, black, or purple grapes, it is essential that the skins spend time soaking in the grape juice to extract the color (anthocyanins), flavors and tannins, resulting in a red wine.  

Once red grapes reach the desired level of ripeness, harvest will commence and fruit will be delivered to the winery to start the winemaking process.  Typically, clusters of red grapes are destemmed to remove the bitter woody parts.  The grapes are then crushed to release the juice from the grape pulp and expose that juice to the skins.  Several intermediate steps can then occur, but eventually the winemaker will add yeast and nutrients to support a smooth fermentation of grape sugars to ethyl alcohol and other flavor components.  

Once fermentation has begun, it is important to promote skin contact with the juice, a process called maceration.  There are three primary methods to enhance skin contact:  1) punch downs, 2) pumpovers, and 3) a technique known as delestage.  If fermentation is done in an open-top container, or in an appropriately equipped tank, the punch down technique can be implemented whereby the grape skins that rise to the surface are periodically pushed back down into the juice.  Breaking up and submerging this “cap” of grape skins can be done manually or mechanically, depending on the available equipment.  Punch downs are most commonly used when fermentations are done in large plastic bins or open-top metal containers.  Punch downs not only enhance juice-skin contact, but also help to moderate temperature.  Fermentation is an exothermic process and higher than desired temperatures can build up in the fermenting juice, especially when insulated by the floating skin cap.  Some air contact at this stage is also desired to support yeast health and activity, and this is accomplished during punch downs.  

A second method to promote juice-skin contact is a pumpover.  This commonly occurs when fermentation is done in a closed top vessel or tank.  Juice is drained from the lower part of the vessel into a small holding tank (pumpover cart) and then pumped back up to the top of the vessel via a hose.  The pumped juice is sprayed over the top of the skin cap, breaking up the cap in much the same way as a punch down.  This process also provides good air contact and a significant measure of cooling.  

Delestage is related to pumpovers in that the juice is pumped (or racked) away from the skin cap, in this case to a separate vessel.  This provides a lot of air contact to the juice and typically results in a softer, less astringent wine with more overall fruit character.  Delestage is certainly labor intensive, and most often involves a series (usually daily) of rack and return steps that will eventually result in the winemaker’s desired level of color and flavor extraction from the skins.  

Once fermentation is completed and the maceration process has reached the desired point, the juice, now red wine, is racked or pumped away from the skins and seeds that remain in the fermentation vessel.  This is termed the free-run wine.  The wet skins are then transferred to a press and the remaining red wine is squeezed out of the pulpy mass.  This is termed the press wine, and can be typically darker, less fruity, as well as more tannic and astringent than the free-run wine.  Winemakers can decide how to use this press wine, either blending back with the free-run juice, enhancing the color and tannin of a different blend, or maybe using a portion as topping wine to replace evaporative losses during barrel aging.  

The point of this blog post is to acquaint you with the importance of grape skins in the production of red wines.  There are many variations on the basic steps outlined above, perhaps the two most important being the temperature of and length of time for the maceration process.  The red color of a wine is not only a part of its charm, but also imparts a number of flavor components, as well as the tannins that typically show up on the finish.  In addition, anthocyanin compounds, those that provide the wine’s color, exhibit antioxidant properties to help red wines age, usually for longer than white wines which do not normally undergo juice-skin contact during the winemaking process.  

A recent article in WineMaker magazine, Oct-Nov 2017 Volume 20 No. 5, entitled Skin Contact Decisions, What’s best for your Wine? by Chik Brenneman, provided the inspiration and a lot of good background information for this Carl’s Corner post.


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