Simply put maceration is the process of soaking crushed grapes, seeds, and stems in a wine must to extract color and aroma compounds as well as tannins. This is where red wines get their color and tannins and it is the lack of maceration that makes white wines so light in color and nearly tannin free.
There are actually several different types of maceration processes. The three most common are the extended maceration, cold soak, and carbonic maceration. Carbonic maceration is a bit different than the other two and will be discussed only briefly.
Maceration may take place either before or during fermentation. A cold soak takes place prior to yeast fermentation while an extended maceration takes place during primary fermentation at least but may be allowed to continue throughout the entire fermentation.
The process begins as soon as the grapes skins have been ruptured. At this time the juice is released from inside the grape and comes in contact with the exterior of the grape skins as well as the stems. To end maceration simply remove the skins, seeds, and stems from your must.
It should be noted that not all grape varietals benefit from maceration. Generally speaking Bordeaux style varietals including Cabernet Sauvignon, Merlot, Cabernet Franc, and Petit Verdot can benefit from this process while other varietals may be too delicate and can become over extracted.
The following are some important things to monitor while carrying out this process on your own wine musts.
The main sources of tannins in wine are grape skins, seeds, stems, and oak. Given that three of the four major sources of tannins are present during maceration monitoring tannin extraction is very important.
You do have some control over how much tannins are extracted by manipulating maceration temperature, duration, and the amount of stems included. By reducing any of these three variables you can reduce the amount of tannins extracted.
If you over extract the tannins you can try to fine them out but you may end up having to age the wine much longer than you originally attended. Over time those tannins will bind together and precipitate out, however you may be waiting several years if this is taken too far.
When maceration takes place during fermentation temperature management becomes a critical part of the wine making process. The yeast produce carbon dioxide during fermentation which makes the skins, seeds, and stems float to the top forming the “cap”.
In a fairly short amount of time the cap becomes quite thick and will insulate the fermenting must below. Fermentation is an exothermic process which means that the process itself gives off heat. The cap traps that heat and can cause your must to get too hot and take on cooked flavors.
To release the heat you must punch down the cap forcing the solids back down into the must. This helps heat escape but also puts the solids back in contact with the must to increase color, aroma, and tannin extraction.
The two things that most often go wrong during an extended maceration are the introduction of spoilage micro-organisms and the formation of volatile acids.
Because of the heat generated and the need to punch down the cap maceration is carried out in open containers (except for carbonic maceration). While the carbon dioxide produced during fermentation will serve to blanket the must and protect it to a degree but you’re still more vulnerable than if you were fermenting in a closed container.
Volatile acids are formed by acetobacter, a spoilage bacteria responsible for turning wine into vinegar. Again, this often happens because your wine is fermenting in an open container. Carbon dioxide does inhibit the growth of acetobacter, however, given that this is one most common problem with an extended maceration it becomes evident that the carbon dioxide is not enough to protect your wine.
Other Types of Maceration
Pink wines are produced by macerating red wine juice on the skins for a very short period of time. Many times the skins are only on the must for a matter of hours.
The wine has just enough time to pick up a little color and perhaps some flavor, however, very little tannins are extracted. This is a great way to make wine from red wine grapes that is consumable much sooner than a full fledged red.
The Cold Soak
The pre-fermentation maceration is known as the cold soak and gets it name due to the practice of chilling the must below 55 degrees F to inhibit yeast fermentation. At these temperatures extraction will move somewhat slowly giving you a lot of control over how much you extract.
Once the optimal extraction has been reached the grape solids and stems should be removed and the must brought back up to a higher temperature so fermentation can begin. At that point you can either let wild yeast from the grape skins get things going or you can innoculate your own yeast.
Carbonic maceration is a special type of maceration that warrants an entire discussion on its own, however, here is a quick overview.
This maceration is characterized by the fermentation of whole grape clusters. The grapes are not destemmed, nor are the skins ruptured in any way. These clusters are put into a special fermentation vat that has been filled with carbon dioxide.
Enzymes naturally present in the grape gradually start an intracellular fermentation, meaning that this fermentation takes place within the grapes themselves.
Photograph by: Mark Smith