Maceration in Winemaking

I recently enjoyed an article by Bob Peak posted in WineMaker Magazine, Virtual Edition (Sep-2020) entitled Maceration Tips and Techniques.  Maceration is a term often tossed out when discussing the wine making process.  It is critically important in producing red wines since most red grapes, like Cabernet Sauvignon, Merlot, and Tempranillo, have colorless pulp (the juicy inside part of the grape) and red-black skins.  Maceration is the technical term for soaking grape skins in grape juice, a necessary step in order to extract color (plus flavors and tannins) from those dark skins into the juice from the pulp to ultimately make a red wine. 

Maceration for red wines usually begins after grapes are harvested and run through a de-stemmer machine and crusher.  This breaks the grapes open so that juice can begin its contact with skins – maceration.  Fermentation – the transformation by yeast of sugar in the grapes to alcohol and carbon dioxide - normally takes place during the early part of maceration.  Carbon dioxide will escape from the fermenting must, pushing grape skins to the surface of the tank or vessel.  This will form a cap that limits skin-to-juice contact, insulates the liquid so that temperature can rise to unacceptable levels, and also minimize air contact that yeast may need to function properly. 

In order to optimize the positive benefits of maceration, punch downs or pump overs are used to break up the grape-skin cap and promote good juice-to-skin contact, as well as help control temperature (by venting) and introduce air.  Over time, typically 2-4 weeks, this maceration process will extract most of the color, flavor compounds, and tannins from the grape skins.  The skins will become significantly lighter in color, often sort of reddish-tan, and as fermentation slows and stops, the amount of carbon dioxide will decrease.  Collectively this will allow the cap of skins to literally collapse and fall to the bottom of the fermenting vessel.  When the cap falls, effective maceration is finished and you have a tank or vessel full of young red wine. 

While maceration, as described above, seems a simple process, there are a number of issues that a winemaker must consider.  One involves over-extraction.  While trying to get as much color as possible out of the grape skins and into the wine seems a good thing, it is possible to extract too much tannin from the skins, and from the seeds that hang around in the tank or vessel.  Too much tannin can make a wine taste tart and astringent, so it is important to monitor the maceration (extraction) period to keep from going overboard. 

There are two major types of polyphenolic compounds in red grape skins that are extracted to make a quality wine.  The color pigments are called anthocyanins, and they are more soluble in water than in alcohol.  More of these compounds can be extracted early in the fermentation process when alcohol levels remain low, so control of fermentation early on can be important.  The second group of compounds are tannins, and they are more soluble in alcohol.  Thus, as fermentation produces more alcohol, more tannins are extracted from the skins (and, unfortunately, the seeds).  For the winemaker, this becomes an issue of managing the maceration process to achieve the optimum color vs. tannin balance.

One method used to maximize extraction of anthocyanin color compounds is to cold-soak the grape juice mixture, delaying the onset of fermentation.  To accomplish this and prevent any unwanted microbial activity before fermentation starts, a small dose of sulfur dioxide is usually added and temperature is held below 50°F for the cold-soak period (1-5 days). 

Carbonic maceration is another technique used by winemakers to produce lighter, early-drinking wines with lots of bright fruit character.  This is commonly used to produce French Beaujolais Nouveau wines.  In this technique, whole grape clusters are placed into the fermentation vessel and juice that is pressed out of the bottom layer of grapes will begin to ferment.  The carbon dioxide gas that is formed limits any air contact and allows an anaerobic fermentation to occur.  Extra carbon dioxide is often pumped into the vessel to keep air out.  Fermentation under these conditions will eventually stop, and the grapes will need to be crushed and exposed to air in order for yeast to finish the job.  Carbonic maceration is becoming more popular with Texas winemakers. 

An important maceration issue is to minimize the extraction of undesirable seed tannins that can be harsh and bitter.  At every stage possible, seeds are removed from the fermentation vessel by pumping or draining liquid through a screen.  Seeds are removed when the juice is either pumped over the cap in the vessel, or in a technique called delestage (rack-and-return), when the juice is pumped into a separate vessel and then returned to contact the skins in the original vessel.  Delestage not only helps to remove seeds, but introduces more air that can help moderate the astringency of tannins in the wine. 

One can see that maceration is an important part of the winemaking process, and that winemakers have a number of issues and options to consider.  So, even though the literal definition of maceration is “soften by soaking,” hopefully this blog post will help readers to appreciate an expanded definition as it pertains to winemaking.