This section contains practical information and several suggestions on how to cope with some common problems encountered during primary fermentation.
Under-ripe Grapes
Trying to make a dry, red table wine from under-ripe grapes is seldom successful. When under-ripe fruit is used, wine flavor and bouquet will be lacking, and wine color will be poor. Most red grape varieties are not ripe until the sugar level reaches 22½ to 23½ Brix. Unfortunately, home winemakers often have little control over when their grapes are picked, and under-ripe fruit is often encountered. Most under-ripe, red grapes are best used to make blush wines. The low alcohol content, skimpy flavors and the high acid levels are more appropriate for light, fruity blush wine.
White grapes are not ripe until the sugar level reaches about 22 Brix and Chardonnay grapes are often picked well above 23 Brix. Riesling grapes, on the other hand, are usually picked at low Brix values before they lose their greenish color. Overripe, white grapes are often best used for producing dessert wines. At the other extreme, under-ripe white grapes can be used to produce excellent sparkling wines.
Adding sugar to under-ripe grapes seldom produces high quality wine. The sugar increases the alcohol content, but the added sugar does nothing to improve the poor color, the puny flavors or the lack of varietal intensity. Sugared wines are usually too alcoholic, pale in color and under flavored, and under-ripe, red grapes often produce wine with unpleasant vegetal characteristics.
Sulfur Dioxide
Making and aging quality table wine without using small quantities of sulfur dioxide is difficult, and most winemakers add small quantities of sulfur dioxide when the grapes are crushed. About 1/2 level teaspoon of sulfite powder for every 100 pounds of grapes is the right amount.
Practically all of the free sulfur dioxide disappears during fermentation, so winemakers add 1/4 level teaspoons of sulfite powder for every five gallons of wine when fermentation is complete. This quantity of sulfite powder will add about 40 milligrams per liter of sulfur dioxide to the new wine. However, about half the sulfur dioxide will combine with other materials in the wine quickly, so only 20 - 30 milligrams per liter of free sulfur dioxide remains in the new wine. The sulfite powder should be dissolved in an ounce or two of water before it is added to the wine.
Wine should always be tested just before bottling time, and the free sulfur dioxide content should be adjusted to about 25 milligrams per liter. Wines bottled with less than 20 to 30 milligrams per liter of free sulfur dioxide oxidize quickly, and they are short lived. Table 15 shows how much sulfite powder is needed to produce 25, 50 and 75 milligrams per liter of sulfur dioxide in various quantities of wine. The values given are in grams. For example, Table 15 shows that 5.8 grams of sulfite powder produce 50 milligrams per liter of SO2 in 15 gallons of wine.
Hydrogen Sulfide
All wine yeast produce small quantities of hydrogen sulfide gas (rotten egg smell) during fermentation, but under normal conditions, the quantities produced are very small and of little consequence. The primary cause of excessive amounts of hydrogen sulfide is elemental sulfur on the grapes. Sulfur is used to control mildew in vineyards, and excessive amounts of sulfur sometimes
remains on the grapes. Here, the winemaker should complete fermentation, and then copper sulfate can be used to remove the hydrogen sulfide. Some types of wine yeast produce more hydrogen sulfide than other types. Montrachet yeast is a particularly bad offender, and it should not be used with grapes containing sulfur residues.
Besides the sulfur problem, yeast often produces objectionable quantities of hydrogen sulfide gas when the grapes lack nitrogen, nutrients or vitamins. Commercial wineries and some home winemakers added small quantities of yeast nutrients and a substance called pantothenic acid to fermentations specifically to reduce the production of hydrogen sulfide. Pantothenic acid is a common vitamin, and it can be purchased at any drugstore.
Crushing by Hand
A mechanical crusher is not necessary for making red wine. Several hundred pounds of fruit can be crushed in a few hours using the following technique. (1) Put a clean plastic milk crate on a clean plastic trash can. (2) Put a few pounds of grapes in the crate. (3) “Scrub” the grapes through the holes in
the bottom of the crate into the trash can. (4) Remove the stems from the crate. (5) Add a few more pounds of fruit and repeat. Some grapes will not be crushed, but whole grapes are not a problem. The juice from the uncrushed grapes will be recovered when the fermentation is pressed.
Punching Down
A handy gadget for punching down small fermentations can be made quickly with a few hand tools. Find a small block of wood and an old broomstick. A 6 x 6 x 12-inch piece of wood is fine. The exact size is not important. Bore a hole in the middle of the wood block, apply glue and insert the broomstick. The new “puncher downer” will be easier to keep clean if it is finished with three or four coats of varnish.
Skin Contact Time
Most of the red pigment and fruit flavors are extracted during the first few days of skin contact. Four or five days of skin contact are enough to produce a quality product when the grapes are ripe. Tannins continue to be extracted for many days.
Cooling Hot Fermentations
Fermentations can become violent when warm red grapes are fermented in hot weather. Much heat is produced, and yeast cells can die when fermentation temperatures exceed 90 degrees for several hours. Such conditions require prompt action, and fermentation temperature must be reduced quickly. Stainless steel containers can be cooled easily by flowing cold water over the outside surfaces. Sometimes small wineries use blocks of dry ice to cool hot fermentations. Home
Gals 25 50 75 of mg/l mg/l mg/l Wine SO2 SO2 SO2 1 0.2 0.4 0.6 2 0.4 0.8 1.2 3 0.6 1.2 1.8 4 0.8 1.6 2.4 5 0.9 1.8 2.7 10 1.8 3.6 5.4 15 2.9 5.8 8.7 20 3.8 7.6 11.4 30 5.7 11.4 17.1 40 7.6 15.2 22.8 50 9.5 19.0 28.5 60 11.4 22.8 34.2
Table 15. Grams of sulfite powder needed to produce 25, 50 and 75 mg/l of SO2
winemakers often fill plastic milk containers with clean water and keep the containers in their freezer. Later, the sealed containers of ice can be placed in hot fermentations to reduce the temperature. All winemakers try to avoid fermenting hot fruit.
Completing Fermentation
Fermentation may be complete when three conditions are met. Check if the bubbling has stopped and make sure the wine is still and quiet. Make sure the hydrometer reads less than zero Brix. Measure the Brix for several days to make sure the hydrometer reading remains constant.
Beginning winemakers often have trouble deciding when fermentation has finished. The above procedure is useful, but the only way to be sure fermentation has finished is to measure the residual sugar in the wine. Clinitest tablets can be purchased at most large drugstores, and these tablets are a very convenient way of measuring small quantities of sugar in wine. Use the “5-drop” method. When the sugar content measures less than 1/4 percent, the wine is considered dry.
Short Range Hydrometers
“Plus and minus five” short-range hydrometers are useful for monitoring sugar content near the end of fermentation. These hydrometers have a special scale. Zero Brix is in the center of the scale, and plus five degrees and minus five degrees run in each direction from the zero point. The scale is large, and 0.1 degree Brix can be read easily.