1. Sulfur Dioxide (optional)
The grapes are treated with a little Sulfur Dioxide as soon as they are brought in. This kills native yeast so that a chosen yeast can be added later. In the case of many of our wines, sulfur is not added so that the ambient yeast can ferment the wine.
2. Sorting and MOG Removal
Grapes are then checked on a sorting table for imperfections and to remove MOG (material other than grapes). Stems are usually removed at this stage, but kept in some instances.
Crushing should be gentle and involves releasing free run juice. Often grapes, such as Pinot Noir, are macerated at low temperatures to extract color and tannin. Heat is also effective as it allows the skin to release color more rapidly, although this can diminish fruit characteristics.
Fermentation is the process in which yeast eats sugar (c6h12o6), becoming ethanol alcohol, carbon dioxide gas and heat. This takes place in inert vessels at temperatures of 30-32 (86-90f). The yeast needs sugar, minerals, nitrogen, and vitamins for food, and will die when alcohol is too high or they run out of nutrients. A good comparison would be a fish tank where the water is not cleaned – the fish will eventually die. It is important to control the temperature, as this will affect the finished wine. Fermenting at lower temperatures retains volatile aromas and fruitiness. Higher temperatures lead to more savory aromas and a darker pigment from the red skins.
There are two main categories of yeast used in fermentation: ambient and cultured. Ambient or indigenous yeasts (naturally on the grapes), was the way all wine was made traditionally. It is more rustic, with ethyl/glycol adding complexity and fullness. A vineyard can have several different strains of yeast present. There is little control over which yeast is dominant. Sometimes unwanted yeast can take over and spoil the wine. This can often be avoided by picking a few grapes and inoculating them beforehand to grow a desired or “house” yeast. It is also called starter yeast.
Today, many winemakers use cultured yeasts, which are quick, predictable, and lead to higher overall alcohol. They also create fewer by-products, making it easier to create wine that tastes “clean". The argument against cultured yeasts is that they can reduce the complexity.
During fermentation, the red skins are in contact with the juice, but will float to the top, creating a cap. It needs to be mixed every few hours to ensure extraction. This can be manually punched down by a paddle or by drawing water from the bottom and pumping it over the top. Larger wineries use rotary fermenters, which resemble a giant blender.
If the skins are removed quickly, the resulting wine will be fruity, low in tannin and short lived. Longer skin contact produces more tannic, age worthy wines.
The free run juice is then drained off, and the wine is pressed again to separate solids. This press juice is kept separate, as it is much higher in tannin and color. If desired, it can be blended back in later to boost a wine's structure and backbone.
6. Malolactic Fermentation
Once the primary fermentation is finished, red wines undergo malolactic fermentation. This takes the stronger malic acid (which is found in green apples), and converts it into creamier lactic acid.
7. Sulfur Dioxide Sulfur Dioxide is again added to stop all fermentations.
The new wine is moved to a holding vessel (often an oak barrel) to begin aging.