Chapter 10.

Beginning winemakers often view crushing and pressing as the most important parts of winemaking. However, these operations are only simple, mechanical operations. Machines do the crushing and the pressing, and if the machines are designed and operated properly, the mechanical operations have little influence on the quality of the wine. Quality depends on many factors such as: where the grapes were grown; when the grapes were picked; the acidity and the pH of the juice; fermentation temperature; skin contact time and other parameters. Wine quality is far more elusive than just being careful how the grapes are mashed and squeezed.

Oxidation and biological changes start when the grapes are picked, and just a few hours can make a significant difference in hot weather. Consequently, winemakers should get to the vineyard early on picking day, and they should be prepared to load, transport and process the fruit as quickly as possible.

Other problems can occur when grapes are picked late in the afternoon on a hot day. Fermentation temperatures can become excessive easily when warm grapes are fermented. High temperature fermentations are not conducive to wine quality. In addition, hot fermentations can kill the yeast and result in stuck fermentations. Commercial wineries cool juice quickly with a heat exchanger and a large refrigeration system. Home winemakers often let warm fruit sit overnight and cool before crushing. Either way, experienced winemakers try to avoid crushing hot grapes.

Crushing breaks the skins of the berries and allows the juice to flow. Crushing should be done with a minimum of grinding and tearing of the grape tissues, and the seeds should never be cracked or broken. Destemming is done to remove the fruit from the stems. Stems contain high levels of phenolic materials, and these materials contribute bitterness and astringency to wine. Excessive quantities of stems can introduce a green, herbaceous characteristic to the wine, and practically all red grapes should be destemmed before fermentation is started.

On the other hand, removing the stems from white grapes is not necessary when the fruit is pressed immediately. Sometimes, not removing stems from white grapes is advantageous. The pulp of some white grape varieties is very slippery, and the slick pulp makes these varieties difficult to press. Varieties like Muscat Alexandria have slick pulp, and they are much easier to press if the stems are left in the must.

Crushing a small quantity of red grapes by hand is practical, but wine yields will be low unless a good wine press is used to separate the new wine from the solids at the end of fermentation. Several hand crushing techniques have been developed, and most of these procedures are satisfactory for handling small quantities. The following procedure is simple, and it can be used for quantities of 200 or 300 pounds.

(1) Place a clean plastic milk crate on a new 32-gallon plastic trash can or any other suitable ridged container.
(2) Place several pounds of grapes in the crate. Smash the clusters with a board or with both hands.
(3) Use a wash board, scrubbing motion with one hand. The grapes and juice will fall through the bottom of the crate into the container, and the stems will remain in the crate.
(4) Remove the bare stems from the crate.
(5) Repeat this procedure.

Not all of the grapes will be crushed, but unbroken berries will not cause problems. When the fermentation is pressed, the wine press will break the skins of the whole berries, and most of the juice will be recovered. In fact, some winemakers deliberately leave some whole berries in their fermentations. These winemakers feel the presence of whole grapes during fermentation increases the fruitiness of the finished wine.

The stems of some grape varieties are abrasive, and the above procedure can be hard on the hands. After an hour or two, fingers can become raw, and hands become badly stained. A pair of heavy rubber gloves may be desirable when large quantities of fruit are crushed by hand.

Crushing grapes with bare feet is a popular notion, but bare feet are not very practical. Grapes stain bare feet black, not red. Grape tannin can cause bare feet to become very dry, and the skin around the toes sometimes cracks. Some varieties of grapes have stiff, sharp stems, and these stems can be uncomfortable to tender, bare feet.

Crushing several hundred pounds of red grapes by foot is quite feasible, but instead of bare feet, an old pair of well-scrubbed rubber boots should be used. A shallow, rigid container of some kind is needed to hold the fruit. Large, plastic mortar boxes are available at large hardware stores, and these shallow boxes make suitable containers. A rhythmic motion should be used when crushing, and the feet should be kept moving around in the container to make sure the grapes in the corners of the container are crushed. Grapes can be slippery, and some kind of hand support will be needed to help maintain balance as the grapes are stomped.

Most home winemakers use a hand crank crusher. Both single and double roller crushers work well, although, some machines are easier to crank than others. These little machines are simple to operate. Place the crusher on top of a suitable container, and fill the hopper with fruit. Turning the crank at a moderate rate pulls the clusters of grapes between the rollers. The grape skins are broken, and the crushed grapes, juice and stems drop into the container.

Hand crank crushers should be adjusted to a convenient working height, and cranking the crusher will be much easier if a clamp is used to hold the machine steady. Most winemakers crush all of the grapes, and then they destem the must. A few winemakers do not destem some red grape varieties at all.

Commercial wineries and some advanced home winemakers use a motor driven crusher/stemmer to process the grapes. A crusher/stemmer crushes the berries and removes the stems in one easy operation. The better designed machines have power driven augers to move the fruit along the hopper into the crushing mechanism. Operation is simple and fast. Grape clusters are dumped into the hopper, and the machine does the rest.

Power crushers have capacities ranging from about 1 ton to more than 50 tons per hour. Even the smallest machines crush and destem large quantities of fruit in a short time. One person is busy keeping the hopper full of grapes.

Power crushers save a great deal of labor, but they are expensive. Small power crushers made of painted steel sell for six or seven hundred dollars. The same machine, fabricated from stainless steel, sells for about $1000. Justifying the expense of a power crusher is difficult for home winemakers unless several barrels of wine are made each year.

The process used to separate the liquid from the grape solids is called "pressing." Squeezing a small amount of juice from white grapes by hand is possible. However, juice yields will be very low, and a surprising amount of labor is required to squeeze sweet pomace by hand. A press of some sort is a practical necessity for making more than a gallon or two of white wine.

Red fermentations are a different situation. As red grapes ferment, alcohol breaks down the cell tissues, and the partially disintegrated pulp gives up the juice more readily. Red pomace is much easier to press than white grapes. Pressing small, red fermentations by hand is easy, and reasonable quantities of wine can be recovered.

The following hand pressing method is suitable if the grapes were crushed completely.

(1) Obtain a clean plastic milk crate, and then cut a piece of 3/4-inch plywood to fit inside the milk crate (the wood should fit loosely).
(2) When fermentation is complete, let the cap rise overnight and carefully syphon off as much "free run" wine as possible.
(3) Place the plastic milk crate on a 32-gallon plastic trash can or other suitable container and put a double layer of plastic window screening in the bottom of the crate.
(4) Nearly fill the crate with the wet pomace and place the plywood on top. Press the pomace by hand and then place a heavy weight on the plywood.
(5) Let the pomace drain for 15 or 20 minutes. Then stir the pomace and repeat step four.

Depending upon the grape variety and the length of the fermentation, 60 to 80 percent of the potential wine can be recovered by hand pressing using this method.

Most home winemakers use a vertical basket press of some kind, and some of these presses are designed to produce high pressures. High press pressures dry the pomace quickly, but high pressures can also produce astringent and bitter wines. Very high press pressures are not desirable, and compound, ratchet type presses must be used with care.

The following procedures produce good results when modest press pressures are used.

(1) Fill the basket with crushed fruit. Add the top plates, the blocks and the press head. Apply a small amount of pressure until a steady flow of juice is produced.
(2) When the flow almost stops, increase the pressure by a small amount and wait again. Large amounts of foam between the basket slats will oxidize the juice, and the foam is an indication that pressure is being applied too rapidly.
(3) Continue increasing the pressure in steps until no more liquid can be obtained.
(4) Disassemble the press by removing the press head, blocks, top plates and the basket.
(5) Remove the pomace "cake" from the press. Place the pomace in a shallow container or on a clean concrete floor and crumble the cake with a shovel.
(6) Replace the basket on the press. Fill the basket with the pomace, reassemble the press and start the next pressing cycle.

Depending on the variety of the grapes, about 150 gallons of high quality juice can be produced from a ton of grapes using these procedures. However, the pomace cake must be crumbled several times to produce 150 gallons of juice. Pressing white grapes with a vertical basket press is a lengthy procedure, and much labor is required to break down the press and crumble the pomace several times

Labor is expensive, so most commercial wineries no longer use vertical basket presses. Instead, most wineries use bladder or membrane horizontal presses because the machines can crumble the pomace cake automatically. Consequently, many press cycles can be used economically, and six or more press cycles are often used to dry the pomace completely. Instead of using high pressures and two or three press cycles, modern horizontal wine presses use low pressures and many cycles to produce 160 to 180 gallons of high quality juice from a ton of fruit.

Winemakers carefully measure the juice when the grapes are crushed, so any needed adjustments can be made before starting fermentation. If sulfur dioxide was not added when the grapes were crushed, it would be added at this time. Small additions of yeast nutrient would be made to grapes grown in vineyards deficient in nitrogen, and tartaric acid would usually be added to fruit grown in warm viticulture regions.

Sulfur dioxide (SO2) helps control wild yeast growth, and SO2 is effective in suppressing several types of bacteria. It also helps reduce oxidation of the must, juice or wine. Big wineries use large quantities of SO2, so they purchase sulfur dioxide gas in steel pressure cylinders. Small wineries and home winemakers generally use potassium metabisulfite (sulfite) crystals to produce sulfur dioxide gas. Generally, 25 to 50 milligrams per liter of sulfur dioxide are added to the grapes before fermentation. Sulfur dioxide is more effective when it is added early in the process. Larger wineries have an SO2 container and a metering pump mounted right on the crusher. The sulfur dioxide is automatically dispensed whenever grapes are going through the crusher. Home winemakers usually add a half teaspoon of sulfite crystals for every 100 pounds of grapes. The sulfite powder is dissolved in a small amount of water, and the solution is added to the grapes as they are being crushed.

A few winemakers do not add sulfur dioxide early. They feel white wines retain better color and malolactic fermentation is easier to complete when no sulfur dioxide is added as the grapes are crushed. These winemakers prefer to make the first sulfur dioxide addition later in the winemaking cycle. However, most experts (UC Davis, Vinquiry, The Wine Lab, etc.) recommend the addition of small quantities of sulfur dioxide early, when the fruit is crushed, and adding sulfur dioxide early is a safer procedure for beginning winemakers.

Many yeast cells are needed to complete fermentation, and yeast must have access to nitrogen, vitamins, minerals and other materials to produce new cells. Some grape varieties like Chardonnay often lack sufficient nitrogen to meet the needs of the yeast, and Chardonnay juice is often difficult to ferment to dryness unless extra nutrients are added. Small wineries and home winemakers seldom have the equipment needed to measure juice nutrients, so these winemakers add small quantities of nutrients to all grapes. Nevertheless, yeast nutrients must be used with care because excessive quantities can produce off-odors in the wine. The manufacturer's directions should always be followed carefully.

Tartaric, malic and citric acids are present in grapes, and several other organic acids are present in wine. The tart taste of wine is directly related to the quantity of acids present. When a wine contains too much or too little acid, the wine will be out of balance. Most grape varieties grown in the interior valleys of California are deficient in acid when fully ripe. When grapes lack acidity, winemakers often add tartaric acid before starting fermentation.

Titratable acidity is a measure of the sum of all the organic acids in juice or wine. Most winemakers prefer to ferment white juice when the titratable acid is in the 0.7 to 0.9 percent (gram/100 milliliters) range. Red musts are often adjusted to a titratable acid of about 0.7 percent before fermentation. The titratable acid of the fruit is always measured at crush time, and any needed acid adjustments are made before fermentation is started. The Table below shows the approximate quantities of tartaric acid to add when juice is deficient in acidity. The acid values are given in grams of acid per gallon of juice. However, acid additions cannot be estimated accurately, so the values given in Table below should be considered rough guides.

TA of Juice	To Obtain 0.7%	To Obtain 0.8%	To Obtain 0.9%
0.40	11.4	15.2	19.0
0.45	9.5	13.3	17.1
0.50	7.6	11.4	15.2
0.55	5.7	9.5	13.3
0.60	3.8	7.6	11.4
0.65	1.9	5.7	9.5
0.70	-	3.8	7.6
0.75	-	1.9	5.7
0.80	-	-	3.8

Grapes grown in cool viticulture regions often contain too much acid, and the finished wine may be too sour. When grapes contain excess acid, winemakers often use calcium carbonate (CaCO3 ) or potassium carbonate (K2CO3 ) to reduce the acid content of juice or must before fermentation is started. These materials precipitate acid salts from the juice, and when most of the acid in the grapes is tartaric acid, substantial acid reductions are possible. Approximately 3.5 grams of calcium carbonate per gallon of juice will reduce the titratable acid by 0.1%. These carbonates must be used with caution because large quantities of either material can raise juice pH to excessively high values. Most winemakers use just enough carbonates to raise the pH of the juice to about 3.3. At this pH value, ML fermentation can usually be relied on to reduce the acid content to a reasonable level.

Another important acid parameter is pH. It gives the winemaker information about just how much sulfur dioxide will be needed to control the wine microorganisms. Juices with low pH values (2.9 - 3.3) require little sulfur dioxide, and medium pH juices (3.4 - 3.6) require an average dose. High pH juices (3.7 - 4.1) often require a prohibitively large addition of sulfur dioxide to control the wine microbes effectively.

When working with grapes grown in a warm area, some winemakers add tartaric acid until the titratable acid is raised to approximately 0.8 percent. Other winemakers simply ignore the titratable acid content, and they add tartaric acid until the pH of the juice drops to about 3.4. Experienced winemakers taste the juice and measure the titratable acid and pH. These winemakers use all of the information available when making pre fermentation acid adjustments.

When grapes are mature, low sugar content is not a problem. Grapes low in sugar were picked too soon, and making high quality wine from immature grapes is difficult. Immature fruit will be high in acid, low in flavor and low in varietal flavors and aromas. Home winemakers are often advised to add sugar to immature fruit. The additional sugar will increase the alcohol content of the wine, but the extra sugar will not reduce the acidity, increase the flavor or improve the weak varietal characteristics. Unless the winemaker is interested in producing wines high in alcohol, adding sugar to underripe grapes is seldom advisable.

In colder growing regions, frost danger sometimes occurs before the grapes are completely ripe, and growers must pick or lose their crops. Here, adding sugar to the juice until the hydrometer reads 20 Brix or so might result in better quality wine. Attempting to make a "big" red wine from such immature fruit is hopeless. Generally, underripe red grapes are best used by making blush wine. Ordinary white table sugar (sucrose) should be added to the juice or must.

Much research has been done on white wine fermentations. This work clearly shows that fresher, more fruity wines are produced when bits of skin and pulp fragments are removed before fermentation. Removing solid materials from the juice results in slower, better controlled fermentations, and the wines have less off-flavors and off-odors. Treating white juices to reduce the amount of suspended material to 1 or 2 percent before fermentation has become a standard winemaking procedure.

Solids can be removed from juices with a centrifuge, by filtration or by cold settling. Centrifuges and lees-filters are expensive pieces of equipment, so smaller wineries and home winemakers generally use a cold settling procedure to clarify white juices.

The procedure is simple. Immediately after pressing, the juice is cooled about 50 degrees so it will not start to ferment. The cold juice is allowed to settle overnight in a closed container. In the morning, the clarified juice is racked off the sediment, and the solid material is discarded. Only clear juice is fermented when making white or blush wines. Sometimes additional clear juice can be obtained by resettling the lees, but the lees must be kept cold or spontaneous fermentation will start.

Crushing is the mechanical operation that breaks the skins of the berries and starts the juice flowing. Crushing should be done with a minimum of grinding and tearing of the grape tissues. Grape seeds should never be broken. Pressing is the mechanical operation used to separate the liquid from the solids. Pressing should be done at low pressures to reduce the extraction of bitter and astringent materials.

Twenty-five to fifty milligrams of sulfur dioxide per liter of juice should be added to the grapes as they are crushed. Juice should be tested, and any needed adjustments should be made before fermentation is started. The quality of all white and blush table wines can be significantly improved by reducing the amount of suspended material to 1 or 2 percent before fermentation. Solids can be removed by settling cold juice and then racking the clear juice off the sediment.

Making an off-dry, low alcohol, blush wine is often the best way to use underripe red grapes.

THE HOME WINEMAKERS MANUAL

by Lum Eisenman