Alcoholic Fermentation

Stainless Steel Tanks

There are many types of fermentation tanks. In fact, any sealed and hermetic container can serve as a fermentation tank (in the Carmel Mizrachi Wineries for example, there are concrete fermentation rooms that have been in use since the British Mandate). The differences betw een the tanks are in the control the winemaker has over the fermenting, mixing and cleaning process. In our winery we use stainless steel fermentation tanks made by “MGT Tanks”, which have a double panel for water passage. Water passing through the tanks allows for computerized temperature control. In addition to the tanks, there is an adjustable floating lid which prevents oxygen from infiltrating the juice.

Immersion with Grape Skins

For most red wines, the color comes from the grape’s skin. In order to derive the anthocyanins and other phenolic components, as well as aroma and tannic substances, found in the skins, it is necessary to immerse the skins together with the juice for a number of days. It is important to mix the juice with the skins a few times a day since the skins tend to surface, and thus do not maintain contact with the juice. Depending on the juice’s volume, mixing can be done manually with a special iron bar or by automatic pumps, which suck the fluid under the floating skins, and spray it back over the skins. With most of our wines, we immerse the skins in low temperatures for 1-2 days before increasing the temperature and adding yeast.

Fermentation

The fermentation process is performed using yeast. From the moment the immersion with the grape skins has been completed, cultured yeast is added to the juice, and a fermentation process begins automatically. The reason for adding cultured yeast, even though there is natural yeast in the juice, is to prevent uncontrolled fermentation, the possibility of an incomplete fermentation (which results in leftover fruit sugar), and the creation of a high level of acetic acid.
During the alcoholic fermentation, the yeast feeds on the sugar in the must, multiplies, and produces alcohol and carbon dioxide. The fermentation process occurs in temperatures that range between 18 to 28 degrees Celsius. If the temperature is too low, this can slow down the process, whereas temperature that is too high can impede the effectiveness of the yeast, and in some cases completely neutralize it. In most cases, a yeast catalyst is added to help complete the fermentation process quickly and efficiently. The completion of the fermentation process occurs when the amount of sugar reaches zero, and the level of alcohol has ceased to rise. There are different types of yeast, and each grape variety has a specific type of yeast that matches it, according to the sugar level in the grapes.

Pressing

Pressing is the process in which pressure is applied to grape skins in order to separate the excess wine found within the grapes’ skins. This process isn’t always necessary, since the free-run juice (the initial fluid liberated after grapes are crushed) is in a high amount and possesses a higher quality. Nevertheless, in order to produce up to 30% additional juice during the winemaking process, the grapes can be pressed. In our winery we use a modern press machine made by “Bucher Vaslin”, in which it is possible to configure the exact amount of pressure that will be applied to the grapes. A strong pressing means liberating a large juice volume, yet one that is excessively tannic or harsh. In contrast, a weak pressing is more likely to liberate a desirable amount of skin components, yet at a lower juice volume.
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