Press and Fermentation

With the crush complete, the time is nigh for dealing with the must. You may have exceeded your energy limits to get to this point but that’s okay, don’t stop now. Carry forth, and either press the must or start fermentation. Depending on the grapes and your wine recipe, you might have an overnight rest for you and the grapes. It is not uncommon for winemakers to start the day before dawn and work past dusk to complete this phase but hold the faith, a glass of wine awaits you at the end of the day (if not before!).

Pressing is straightforward, squeeze the must to extract juice leaving the pulp and seeds behind. The use of a mechanical press is the most efficient approach. If you don’t have a press, you may be able to rent one from a local winemaking retailer. If you’re processing a small batch, several manual methods can be employed, for example, filling a large pillow case or cheesecloth with the must and squeezing by hand.

Yeast (find a winemaking yeast chart here), is the catalyst converting sugar in the must or juice to an alcoholic beverage during fermentation. The greater the sugar level at the beginning, the more alcoholic the final wine. It can be fermented to dryness or short of dryness, depending on the varietal and approach desired by the winemaker. A Hydrometer is used to track the sugar level in the ferment, informing sugar levels at the beginning and end of fermentation.

The approach between red and white fermentation differs. Red must is commonly fermented in open containers, while white juice containers are closed. Exposure to oxygen during fermentation serves to oxidize the wine, so exposure must be limited. Fermenting red must is protected from oxygen due to the formation of a grape pulp cap along the top, which acts as an oxygen barrier. A closed container is required for white juice since the grape pulp was removed during pressing.

As you may have guessed from the differing fermentation approaches, the steps involved in pressing and fermenting red and white diverge after the crush.

Red grape must is first fermented before being pressed. The fermentation process and time involved extract the necessary color and flavors associated with red wine. Though for the extractions and color to be fully expressed the aforementioned cap along the top must be punched down or for some commercial winemakers, poured over mixing the ferment one to three times daily. 

Conversely, in most cases, white grape must moves quickly after the crush to the press. Pressing quickly retains the lighter color and fruit flavors associated with white wine. “In most cases”, recognizes certain white varietals and winemakers may desire to hold the must for a short period before pressing, to achieve certain flavor and color profiles.

Rosé is made of red grapes and is processed similarly to white wine. After crushing, the must is held for a period of time to extract the level of color and flavor desired by the winemaker, then sent to the press before fermentation.

Another fermentation consideration involves whether to conduct malolactic fermentation (MLF). MLF is a process of converting malic acid into wine-producing lactic acid. Lactic acid is found in milk and the result for wine softens and rounds the flavor lessening acid and fruit characteristics. MLF is commonly conducted for reds and certain whites, such as Chardonnay. Sometimes referred to as a secondary fermentation, MLF can run concurrently with the primary fermentation or right after the primary is complete.