Batch Process of Wine Making

Introduction

The homemade production of wine is a fun and challenging hobby that many people can enjoy. In this paper the reader will be taken through several different steps and processes that must be accomplished for your wine to be of satisfactory flavor and clarity.

Crushing and stemming

This first step may be performed by hand or by machine. For handling a ton or more of grapes, use a mechanical crusher-stemmer. Using a small crusher-stemmer, two persons can crush and stem a ton of grapes in about one hour. To collect the crushed grapes, which are also called the must, the machine is placed and supported above a container. A large polyethylene plastic tub or garbage can is sufficient. The important objective is to minimize bitterness by thoroughly crushing the berries without macerating the seeds, and while recovering all of the skins and juice in the must. After stemming and crushing, the fermentors are filled with the must to about two-thirds capacity, to avoid foaming-over during fermentation.

After all of the must has been poured into the fermentors and the sulfur dioxide has been added, the fermentors should be covered with cheesecloth or plastic to keep out insects. Temperature, total soluble solids, titratable acidity, and the free and total SO2 of the must in each fermentor should be determined and the results recorded.

Adding sulfur dioxide

Sulfur dioxide (SO2) is a chemical compound that has been used in winemaking for more than a century. Because it is known that wine yeast produce small amounts of SO2 during fermentation, SO2 can be considered a natural constituent of wine.

Judicious and moderate use of SO2 has long been recommended. Recent research shows that the best quality wines are made when SO2 has been used both before and after fermentation.

For grapes free of mildew, rot, or mold, usually from 50 to 100 parts per million (ppm) is used or about 75 ppm is adequate. This mild antiseptic is commonly used in the form of potassium metabisulfite (K2S2O5), and is available from home wine making suppliers. To obtain 75 ppm of SO2, add ј ounce to each 10 gallons of juice or must. For grapes that have appreciable amounts of moldiness, rot, or broken berries, use twice this amount of SO2. To add SO2, dissolve the metabisulfite in a small portion of the juice; then add this back to the bulk of the must to be treated and mixed thoroughly. Allow this mixture to stand about 2 hours before adding the wine yeast starter culture.

Alcoholic fermentation

Grape wine is the alcoholic product of the fermentation of grape juice. The essential feature of this fermentation is the conversion of the grape sugars, glucose and fructose, to ethyl alcohol (ethanol), carbon dioxide (released as gas), and flavor components. This complex process is accomplished by living yeast cells.

The alcohol produced through fermentation is a wine's major flavor component. It also affects the solubility of many wine constituents. Some is used in forming other flavor compounds. It also enhances wine's resistance to spoilage. Wines traditionally are classified according to their alcoholic content.

Fermentation in wine making is not only fascinating but it is critical to success. Typically, there are three distinct stages.

1. A resting period of 12 to 24 hours, during which yeast cells grow and increase in sufficient numbers to commence the fermentation.

2. Vigorous activity of 2 to 3 days, during which the yeast rapidly ferments one-half to two-thirds of the sugar to alcohol and carbon dioxide gas-the latter development is accompanied by frothing-and the skins rise to the surface, become compact, and form the "cap".

3. A more or less quiet stage of relatively slow fermentation for 3 to 4 days after pressing the partially fermented juice off the skins.

Pressing

Basket presses are available in various sizes, either hand-operated, motor driven, or hydraulic driven. The basket press, probably the most expensive piece of equipment needed in home wine making, is also one of the most worthwhile investments. A properly cared for press should provide a lifetime of trouble-free service.

Fill the basket with partially fermented must and allow the liquid portion to flow freely into a stainless steel bucket or polyethylene plastic pail covered with plastic window screen to catch solids. Discard solids from the screen surface as needed. This portion of the partially fermented juice or wine is called the "free-run". After all of it has been collected, apply pressure slowly and not for too long a time. Too rapid application of pressure causes the wet solids to squirt through the basket openings, which defeats the basket operation.

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