It is a tradition in Macedonia when preparing wine, to keep several bottles of unfermented grape juice and drink it as juice the same day or maximum till next day, because the process of fermentation of the juice is very fast. We call this juice shira (a must in English).
Shira is a sweet wine, unfermented grape juice. More broadly, the must is a fresh fruit juice (usually grape juice) obtained by crushing, draining and pressing the fruit. The rest (solid part) that contains the seeds, skin, and stems of the fruit is called a pomace (komina). Making must is the first step in wine production.
Wine production

The duration of keeping the pomace and must together is important for the character of the wine. When the winery estimates that it is time, the must is taken out from the pomace, and pressed to extract the remaining juice. Fermentation can be natural (without additives), but in order to evenly boil and prevent the interruption of fermentation, wine yeast is added. Water can be added to the pomace, left for 24 hours and then used for wine production. In Macedonia, most often the pomace is used for production of rakia. This kind of rakija is called a komina.

The must can be also used for making wine vinegar.

Preserving the must
If this natural and healthy vitamin-mineral drink is prepared in the right way, it can preserve the nice sweet taste for a longer period without preservatives. The procedure is different from the one when the wine is made from the must. The most important thing is that the grapes after the harvest are well-washed and disinfected. This is done in order to destroy the whole spontaneous microflora on the skin of the grains, and also the yeast fungi, whose activity turns the must into wine.

"The grapes are disinfected by immersion in a larger kettle with water, where 20 grams of vinegar is added to 100 liters of water. After disinfection, the grapes are washed well in clean water and dipped in the water. The best quality grape juice is obtained from the drained grapes, while the remaining must is used for wine. The juice is then deposited to remove the rough dirt. After the 24-hour precipitation, cleared must is collected and transferred and for full clarity, 150 grams of dissolved bentonite are added to 100 liters must.

Then there is a two-day deposition and transfer. It becomes a completely clear grape juice, which can be immediately used. However, in order to maintain organic-nutritional characteristics without preservatives, even until the new harvest, a procedure similar to the preparation of tomato juice for winter should be applied. The must isn't biledr, but only heated in an enameled container for 10 minutes at a temperature of 70 C degrees. This pasteurized must is collected in disinfected bottles, which are sealed with wine caps and placed in horizontal position on the basement shelves.