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At the highest quality of retention, unopened grape juice can be stored for 6–12 months unrefrigerated. [8] After opening, grape juice can be stored for approximately 7–10 days in the refrigerator before spoilage occurs. [11] Aseptic processing can also be used, which requires the grape juice to be sterilized before packaging. [8]
The natural occurrence of fermentation means it was probably first observed long ago by humans. [3] The earliest uses of the word "fermentation" in relation to winemaking was in reference to the apparent "boiling" within the must that came from the anaerobic reaction of the yeast to the sugars in the grape juice and the release of carbon dioxide.
The length of time the pomace stays in the juice is critical for the final character of the wine. When the winemaker judges the time to be right, the juice is drained off the pomace, which is then pressed to extract the juice retained by the matrix.
For red wines, the juice is fermented with the grape skins to extract colour, tannins and flavour. This process can take anywhere from a few days to several weeks, depending on the desired style ...
Viognier juice in the press pan after being pressed. In winemaking, pressing is the process where juice is extracted from the grapes with the aid of a wine-press, by hand, or even by the weight of the grape berries and clusters. [1]
The processing time of the juice is calculated by multiplying the number of pulses by the effective pulse duration. The high voltage of the pulses produces an electric field that results in the inactivation of microbes that may be present in the juice. The PEF temperatures are below the temperatures used in thermal processing.
This minimizes contact between grape juice and skins (as in the making of Blanc de noirs sparkling wine, which is derived from Pinot noir, a red vinifera grape). An alternative method to maceration is hot press or thermovinification. [13] In this practice, winemakers heat up the grapes to extract the juice rather than pressing using a pressure ...
Conventional alcoholic fermentation involves crushing the grapes to free the juice and pulp from the skin with yeast serving to convert sugar into ethanol. Carbonic maceration ferments most of the juice while it is still inside the grape, although grapes at the bottom of the vessel are crushed by gravity and undergo conventional fermentation.