Pomace, or marc (; from French marc in French pronounced as /maʁ/), is the solid remains of grapes, olives, or other fruit after pressing for juice or oil. It contains the skins, pulp, seeds, and stems of the fruit.
Grape pomace has traditionally been used to produce pomace brandy (such as grappa, orujo, törkölypálinka, zivania). Today, it is mostly used as fodder, as fertilizer, or for the extraction of bioactive compounds like polyphenols.[1]
The ancient Greeks and Romans used grape pomace to create an inferior class of wine given to slaves and laborers. The grapes were first pressed twice and the resulting pomace was then soaked in water for another day and pressed a third time and fermented. The resulting liquid produced a thin, weak, and thirst-quenching wine with an alcohol content around 3 or 4%, now known as piquette in English and French and as Italian: graspia or Italian: vin piccolo in Italian.[3] Piquette was also widely available during the Middle Ages. As medieval wines were not usually fermented to dryness, medieval piquette retained a degree of residual sugar.
Pomace from various sourcesparticularly fish and castor beanswas also used in the early modern period for fertilizer.[2]
Apple pomace is often used to produce pectin and can be used to make ciderkin, a weak cider, as well as white cider, a strong and colourless alcoholic drink.[4]
See main article: Pomace brandy. Grape pomace is used to produce pomace brandy and piquette. Most wine-producing cultures began making some type of pomace brandy after the principles of distillation were understood.
See main article: Winemaking. Pomace in winemaking differs, depending upon whether white wine or red wine is being produced.
In red wine production, pomace is produced after the free run juice (the juice created before pressing by the weight of gravity) is poured off, leaving behind dark blackish-red pomace consisting of grape skins and stems. The color of red wine is derived from skin contact during the maceration period, which sometimes includes partial fermentation. The resulting pomace is more alcoholic and tannic than pomace produced from white wine production. Pomace from the Italian wine Amarone is macerated in Valpolicella wine to produce Ripasso.
In white wine production, grapes are separated from their skins, then pressed to obtain juice. The skin pomace is a pale, greenish-brown color, and contains residual sugars and tannins. This pomace is used in brandy production.
Pomace is produced in large quantities in wine production, making its disposal an important environmental consideration. Some wineries use the material as fertilizer, while others are selling it to biogas companies for renewable energy. As envisioned, pomace would be introduced into anaerobic digesters that contain microorganisms that aid in its decomposition and produce methane gas that could be burnt to generate power.[5]
Specific polyphenols in red wine pomace may be beneficial for dental hygiene. A study conducted at the Eastman Dental Center found that these polyphenols interfere with Streptococcus mutans, the bacterium in the mouth that causes tooth decay. Professor Hyun Koo, the lead researcher of the study, hoped as of 2008 to isolate these polyphenols to produce new mouthwashes that will help protect against cavities.[6]
Grape pomace is also used in the oil and gas industry as a lost circulation material in oil-based drilling muds due to the pomace being fibrous and tannin-rich.
A 2004 study conducted by Erciyes University in Turkey found that pomace can also act as a natural food preservative that interferes with E. coli, Salmonella and Staphylococcus bacteria. Researchers pulverised the dried pomace from the white Turkish wine grape Emir Karasi and red Kalecik Karasi grapes; this was mixed with ethyl acetate, methanol or water and exposed to 14 different types of food bacteria. All 14 bacteria were inhibited to some degree by the pomace – depending on the grape variety and the concentration of the extract. The red wine Kalecik Karasi grape was the most effective; the researchers believed this was due to the higher concentration of polyphenols in red wine grape skins.[7]
Oenocyanin, a natural red dye and food-coloring agent, is produced from grape pomace. Tartrates (potassium bitartrate, 'cream of tartar') and grape polyphenols can also be manufactured from grape pomace.[8]
Apple pomace has long been a traditional feed for various kinds of livestock.[9] The use of grape pomace as livestock feed is encouraged in order to reduce the release of grape processing residues in the environment, which can lead to serious pollution.[10]
Apple pomace was used, in conjunction with whey, to flavor the first iteration of Fanta soft drink in Germany during World War II. This was done because wartime embargoes limited Coca-Cola of Germany's ability to import and manufacture the American beverage.
Apple pomace can also be milled in order to create apple flour, also known as apple pomace flour.
According to the Canadian Food and Drug Regulations, pomace can be a potable alcoholic distillate or a mixture of potable alcoholic distillates obtained by distilled skin and pulp of sound ripe fruit after removal of the fruit juice, wine or fruit wine. Pomace may contain caramel, fruit, botanical substances, flavoring and flavoring preparations. Pomace may be described on its label as "(name of the fruit) Pomace" or "(name of the fruit) Marc" if all of the skin and pulp of the fruit used to make the pomace originate from the particular fruit.[11]