Chapter 9.

Chardonnay and Pinot Noir are early ripening grape varieties, and they are among the first grapes picked each year. Cabernet Sauvignon, Nebbiolo and Carignane are late varieties, and these varieties are the last grape varieties picked. In southern California, the crush usually starts in mid August and ends in October. Harvest times vary from year to year. In early years, the grapes are picked two or three weeks earlier than normal. In late years, Carignane grapes are often picked in late October. The start of the grape harvest depends primarily on accumulated heat. The grape harvest in Northern coastal regions starts about three weeks later than in Southern California. For a given location, most of the grapes are harvested each year during a seven or eight-week period.

High quality wine can only be made from high quality grapes. The quality of the grapes always determines the potential quality of the wine. If the grapes are picked too early or too late, wine quality will suffer. Wine made from under-ripe grapes often has a "green" characteristic. These wines contain excess acid, lack color, lack flavor intensity and lack varietal character. When grapes are picked too late, the wine is high in alcohol and low in acidity. Often, wines produced from overripe fruit have stewed fruit, raisin or prune flavors. Quality wine can only be made from high quality, properly ripened fruit, and deciding exactly when to pick the grapes is the most important decision a winemaker makes each crush season.

Unfortunately, ripe wine grapes are very perishable, and grapes are at their best for just a few days in warm growing areas. The short harvest interval and crop sizes of several tons per acre create serious harvest problems for winemakers. Coordinating harvest activities and crush operations is difficult, and crush seasons are busy and sometimes hectic periods at any winery.

When to pick the grapes is such an important decision that most winemakers start sampling grapes several weeks before harvest time. As harvest day approaches, the winemaker goes to the vineyard every few days to sample the fruit. He looks at the condition of the vines, and he tests the texture of the berries by gently squeezing them between his thumb and forefinger. The grapes are visually examined and tasted. The pulp is smelled, and the color of the seeds are examined. Then the winemaker collects a representative sample of several hundred berries from each vineyard. When the winemaker returns to the winery, he measures the titratable acid, pH and sugar content of the sample grapes.

Tartaric and malic acids make up about 90 percent of the total organic acid content in grapes. Malic acid is found in many different varieties of fruit, but only grapes contain significant amounts of tartaric acid. The amounts of tartaric acid and malic acid are about equal when grapes start to change color and soften (veraison), and the quantity of tartaric acid remains roughly constant throughout the ripening period. On the other hand, the quantity of malic acid decreases as the grapes ripen, and the loss of malic acid results in a gradual decrease in the total acid content during the ripening period. In hot growing regions, much of the malic acid is gone by harvest time. Depending upon the grape variety and the growing conditions, grape juice contains 1.5 to 5 times more tartaric acid than malic acid.

In cold viticulture regions, ripe grapes have an acid content ranging from 0.7 to 1.3 percent. Such high acidity often results in excessively tart wine. To avoid excess tartness, winemakers in cold growing regions use special procedures to reduce wine acidity. The situation is quite different when grapes are grown in warm regions like the interior valleys of California. Here, the acid content of ripe grapes often falls between 0.4 and 0.8 percent. Grapes grown in such warm climates often have too little acidity, and wine produced from grapes low in acidity is often bland and flat tasting. Besides producing bland wines, fermenting grapes low in acidity often results in other problems, and adding acid to grapes grown in warm regions is a standard winemaking practice. Large acid additions are best made before fermentation is started.

The acid content of grapes (or wine) is usually measured using a procedure called titration. Sometimes winemakers call the acid content "total acid," but the preferred term is "titratable acid." Titration measures the sum of all the different types of acids in the wine, but the results are expressed as if all of the acids were tartaric acid. French winemakers use a different convention. They express titratable acid as if all the acids present were sulfuric acid. These different customs result in different numbers, and sometimes novice winemakers are confused by the different conventions.

Grape acids differ considerably in strength. Tartaric acid is stronger than malic acid, and malic acid is stronger than citric acid. A quantity called "pH" is used to measure the strength of the acids, and pH is defined using an inverse, logarithmic scale. High acid grapes have a low pH, and low acid grapes have a high pH because of the upside down scale. pH values range from 2.8 to 4.2 for juices obtained from sound, ripe grapes. As grapes ripen, malic acid is lost, and the acid content decreases.

As the acidity decreases, the pH value of the grape juice slowly increases. Late in the ripening process, just as the grapes are reaching maturity, potassium ions start accumulating in the juice. The potassium ions interact with acids in the grapes, and this interaction causes the pH of the juice to increase more rapidly just as the grapes are reaching maturity. Several weeks before expected harvest time, winemakers start their annual crush routine. They visit the vineyards every few days and collect grape samples. Then the grape samples are tested for sugar, titratable acid and the pH in the winery laboratory. Winemakers use the pH, sugar and TA data to help decide when the grapes should be picked.

Historically, sugar content was the primary indicator of grape ripeness, and many growers still rely on sugar readings to decide when the grapes are ripe. Consequently, obtaining accurate sugar measurements is important. Grape sugar content is usually measured in units of degrees Brix, and the measurement is made with a hydrometer or a hand-held, optical instrument called a refractometer. The accuracy of either instrument depends upon temperature. Most instruments are calibrated at a temperature of 68 degrees Fahrenheit, and a correction must be applied to the readings when measurements are made at any other temperature. Some refractometers are temperature compensated, and the compensation greatly reduces the temperature error.

Refractometers are handy sugar measurement instruments because they can measure the sugar content of a single drop of juice with good accuracy. In most instruments, each degree is subdivided into five parts, and a value of 0.2 Brix can be read directly on the refractometer scale. Well built, temperature compensated refractometers cost about $300, and good uncompensated instruments can be purchased for less than $150. Most winemakers prefer compensated instruments, but data obtained with an uncompensated refractometer can easily be corrected for temperature. The major advantage of refractometers is their ability to measure very small samples of juice quickly and easily.

Both short range (16 to 25 Brix) and long range (-2 to 30 Brix) hydrometers are available. Short range instruments cost about twenty dollars, and long range hydrometers cost less than ten dollars. The scale on good, short range hydrometers can be read directly to 0.1 Brix, and good hydrometers have a "certified" calibration. About 100 milliliters of juice are required to make a measurement when hydrometers are used with small diameter cylinders. Despite their low cost, good hydrometers are more accurate than hand held refractometers.0. Temperature corrections for Brix hydrometers.

TEMP	CORRECTION
56	-0.38
58	-0.32
60	-0.26
62	-0.20
64	-0.14
66	-0.08
68	0.00
70	+0.07
72	+0.14
74	+0.22
76	+0.30
78	+0.38
80	+0.46
82	+0.54
84	+0.62
86	+0.71
88	+0.80

The accuracy of measurements taken with hydrometers also depends on temperature. Hydrometers must be used at their calibration temperature, or a correction for temperature must be applied to the readings. A typical hydrometer correction chart is shown in Table 8. High accuracy and low cost are the major advantages of a Brix hydrometer. Some winemakers avoid temperature corrections by making sure the temperature of the grapes and the hydrometer is at the calibration temperature. Grape samples are brought into the winery lab and allowed to come to temperature equilibrium. When the grapes have cooled to room-temperature, the grapes and hydrometer are at (or close to) the calibration temperature, and corrections are not needed.

Making accurate sugar measurements in large vineyards is not easy. The grapes from a single cluster contain different amounts of sugar. Grapes from high on the cluster normally contain more sugar than grapes from the bottom of the cluster. Grapes taken from clusters exposed to the sun contain more sugar than grapes taken from clusters growing in heavy shade. Grapes taken from vines growing in different parts of a vineyard can have large differences in sugar content. Variations of two degrees Brix often occurs over a ten-acre vineyard block.

Because of the large variations in sugar content, large size samples must be collected to produce accurate results. A sample of about 100 individual berries is considered the minimum sample size for small vineyards, and many winemakers prefer samples containing 200 to 1000 berries.

Besides a large sample size, measurement accuracy also depends on how sample grapes are collected. The grapes must be collected in a consistent way from the area to be picked, or the results will be misleading. For example, an adequate uniform and reasonable size sample could be collected by picking one grape from each vine in a 100-vine vineyard. In a tiny vineyard of 30 vines, picking one grape from three or four clusters on each vine would be appropriate. A much larger sample would be picked in vineyards containing several thousand vines. Here, a uniform sample of several hundred grapes would be collected by picking one grape from every fourth or fifth vine.

Collecting a representative sample of grapes from the area to be picked is very important. If the intent is to pick the first six rows in a block of vines, then only first six rows should be sampled. If the whole vineyard will be picked, then the entire vineyard should be sampled.

The following grape collection procedure has been used for some time. This method produces good results, and the procedure is particularly useful when several different vineyard blocks are sampled on the same day.

(1). A 1 quart size, heavy weight, zip-seal "baggy" is used to collect the grapes. The date and the vineyard block being sampled can be written on the baggy with a "magic marker."

(2). Grapes can be collected from each vine, every other vine, every fifth vine, etc., but at least 100 grapes should be collected from the vineyard block of interest.

(3). Most of the sample grapes should be picked from the bottom of the clusters (watch out for bees and wasps), and most of the sample grapes should be picked from clusters growing in the heavy shade.

(4). The baggy should be sealed and the grapes kept cool until the measurements have been made.

The measurement procedure described below assumes the sugar content is being measured with a short range hydrometer. However, once the juice has been collected (at the end of step three), the sugar could be measured with a refractometer.

(1). Remove any air from the baggy. Seal the baggy tightly, and lay it on a smooth flat surface. Use a heavy, flat-bottomed glass tumbler to crush the grapes in the baggy gently. Crush all the grapes, but be careful not to press too hard because the seeds can puncture the baggy and cause messy leaks.

(2). Use both hands and knead the mass of grapes in the baggy for several seconds to extract the juice.

(3). Unseal the baggy and hold the lip of the baggy over a hydrometer cylinder with the left hand, and carefully squeeze the juice out of the baggy with the right hand. (With a little practice, the seeds, skins and pulp can be retained in the baggy).

(4). When the cylinder is about half full of juice, carefully lower the hydrometer into the cylinder.

(6). Wait a minute to let the hydrometer settle. Then tap the cylinder a few times to make sure the hydrometer is not "stuck" to the side of the cylinder.

(7). Read the hydrometer scale at the bottom of the meniscus and record the Brix value. Remove the hydrometer from the sample, measure the temperature of the juice with a thermometer and record the temperature value.

(8). Use a hydrometer temperature correction chart (Table 8) and apply the appropriate correction to the measured value.

Besides sugar content, most winemakers also measure the titratable acid and the pH of the sample juice.

High quality wine can only be made from high quality grapes, and grapes are in prime condition for just a few days. Picking wine grapes near optimum ripeness is very important, so winemakers start sampling the grapes well before harvest time. Large size samples are collected, and a variety of measurements are used to decide when to pick the grapes each crush season.

Sugar content is the traditional way of judging grape ripeness, but winemakers also measure acidity and pH. In addition, winemakers also carefully smell and taste the flavor characteristics of the sample juice. Each winemaker has his or her way of noting and recording grape flavor attributes, and experienced winemakers make his or her picking decisions based on many different factors.

THE HOME WINEMAKERS MANUAL

by Lum Eisenman