The process of winemaking involves the production of wine that is stored at a temperature that allows it to mature. There are various stages involved in the process including pre-fermentation, primary fermentation, malolactic fermentation, and post-fermentation.
Preparation of the grapes
There are several steps involved in the preparation of the grapes for winemaking. Each stage may require a different approach. In addition, each grape variety has a different level of sugar. This can affect the final product.
First, the grapes need to be picked. The timing of picking depends on the type of grapes and region.
Grapes can be picked manually or mechanically. Machines are used to harvest grapes for mass production. It is best to avoid using machines during the harvesting process as they can hurt the grapes.
Traditionally, grapes were crushed by hand. Today, there are several mechanical methods for the crushing of grapes.
Crushing involves breaking the skins of the grapes. The skins should be broken with minimal tearing. Keeping the white skins in contact with the juice can help increase the amount of color and flavor extraction.
Vinification
Vinification is the process of making wine from grapes. It involves a number of steps, which are taken from the time of harvest until the final liquid is bottled. These steps vary according to the type of wine that is produced.
Before a wine is bottled, it undergoes a process called fining. This is the removal of sediment and other solids. The most commonly used agent for fining is gelatin.
Another method is hydrometers, which measure the specific gravity of the wine. Other methods are cellulose pads and membrane filters.
Winemaking requires many phases, including grape selection, harvesting, and the production of pomace and lees. Winemakers can choose to add additional ingredients to soften the taste of the wine or to adjust the acid levels.
Aside from the grapes, the other ingredients that are used in winemaking include yeasts, sugar, and alcohol. Yeasts are a fungus that belong to the saccharomyces genus. They produce energy to proliferate and to transform sugars into alcohol.
Primary fermentation
Primary fermentation is the process by which yeast converts the sugars in grape juice into alcohol. The process takes from one to three weeks.
There are a number of factors that influence the fermentation process. Temperature is a key factor. During primary fermentation, the temperature should be between 70 and 75 degrees. This is a range that will allow the yeast to be activated and multiply.
Yeast will produce carbon dioxide during the primary fermentation process. These gaseous bubbles are what you will see in the must and bottle. Carbon dioxide is a biochemical compound that contributes to the distinct aroma of your wine.
A food grade bucket or a large open container is best for primary fermentation. You will want to clean the container before you start the process.
Malolactic fermentation
Malolactic fermentation in winemaking is a process that involves the conversion of malic acid to lactic acid. This process is facilitated by lactic acid bacteria, and occurs after the alcoholic fermentation of yeast. During this time, the wine is less fruity and softer in character. The result is a more complex wine.
Wine contains various volatile aldehydes, which contribute important sensory properties. Acetaldehyde is the most abundant aldehyde in wine and has important effects on the colour, ageing and stability of the wine. Diacetyl is also present in wine and plays an important role in its buttery aroma. Several factors can affect diacetyl formation, including the type of LAB, the concentration of sugars and citrates, and oxygen.
The acetaldehyde in wine can be converted to acetoin by a diacetyl reductase. It can be decarboxylated by some lactic acid bacteria, especially those of the Oenococcus oeni family.
Post-fermentation
Fermentation is a complex process, as it involves many chemical reactions to turn sugar into alcohol. It also gives wine its iconic smells and flavours.
Post-fermentation maceration is the process of extracting phenolic compounds from the grape juice. The length of this process can vary from a few days to a couple of months. However, the ideal duration of the maceration will depend on the winemaker’s preferences and the variety of grapes used.
Maceration is usually done in sealed vessels. This helps to prevent leakage. Some winemakers leave fine lees in contact with the liquid.
Other methods include skin maceration, which is traditional in the Rhone Valley and Piemonte. In Australia, this practice is often used with Cabernet Sauvignon.
The presence of yeast lees can affect the aroma of the final wine. During the process, acetic acid can form on the cap of the skins and seeds.
