Destemming and tannins

Talking about stemming

Grapes and the stalk

The grape bunch is the fruit of the plant of the vine. It is made by the a wooden part called stalk, to which the round fruits, called grapes, are linked. The stalk is branched and woody. It is made of water, tannins, cellulose and pectine. The grape, instead, contains the seeds located in the central core. Around them the pulp is divided into three layers. Starting from the inside we can find the core area that contains malic acid and sugar.

Then there is the intermediate zone rich in tartaric acid and sugars. Finally, the peripheral area rich in tannins, polyphenols, aromas, acidity and sugars. The peel encloses the pulp and its thickness varies according to the vine. The anthocyanins in the skin are responsible for the color in the red grapes. Flavoses, on the other hand, are responsible for the color of white grapes.

Destemming: less tannins, more alcohol

Destemming is the operation that separates the grape from the rasp. It must be done before pressing. If it doesn’t take place, the wine obtained will have a high amount of tannins with the consequent astringency and bitter taste. The stalk also contains lots of water that can dilute the alcohol and fermentation could be slower.

Tannins: how do you perceive it?

The tannicity of a red wine depends on the vinification system. White wines do not have this feature. The maceration time here is fundamental. The longer the peels stay in contact with the liquid, the greater the tannicity in the wine will be.

The peels contribute to the release of tannins to a greater extent than the seeds. The sensation of astringency we perceive when tasting wine shows the presence of tannins. They are substances that, when in contact with saliva, bind and precipitate. The same feeling is felt when eating rough fruit.

All red wines have more or less tannins, but in a different way. The quality of the grapes, the vine and winemaking are the elements that depend on tannins. In great red wines, addressed for aging, this characteristic becomes weaker as time passes. The barrel has the ability to soften the bitter starting tannins by releasing the gallic tannins that give a sweet feeling of aging. Destemming is therefore one of the systems that allows you to manage the balance of a wine.

Destemming machines

The technology really helps the operations of stemming. Over the last few years, machines are able to complete the operation in a perfect way. They can be made of enamelled steel or stainless steel. Stainless steel is indicated for professional use, as the use is guaranteed for a long time. The systems with which they are produced allow hygiene and cleaning. In the upper tank the whole bunches enter and they are transported to the pressing point. A metallic net associated with a detonating shaft allows the effective removal of the grapes from the stalk. A centrifugal pump also facilitates the passage of the must, directly into the fermentation vessel.
The hourly amount of grapes that can be processed varies from 2000 kg to smaller models up to 3000 kg and above, for professional models. The engine is HP 2 or 2.5 single phase with starting capacitor, depending on the size of the machine.

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