DECIDING WHEN TO PICK
By
Lum Eisenman


Under-ripe red grapes are low in sugar, low in flavor, low in color and high in acid. Wines made from under-ripe grapes can be overly tart, and they often have herbaceous, green bean or bell pepper flavors. Wines made from under-ripe grapes also have poor color, low flavor intensity and often lack varietal character.

Overripe, red grapes are high in sugar, low in acid and high in color. Wine made from overripe grapes are high in alcohol, and they can taste “flat” or bland because they are too low in acidity. Furthermore, wines produced from overripe grapes often have “cooked fruit” or prune flavors.

Properly ripened red grapes have the correct amount of sugar, acid, color, and good varietal character and flavor intensity. Wines made from properly ripened grapes will have the correct amount of alcohol, good color and flavor intensity, and good varietal character with some “red fruit” flavors.

HARVEST DECISIONS

To make high quality wine, the grapes must be picked at the optimum time, but determining when to pick the grapes is not always an easy task.

Brix
Sugar content has been used as the primary indicator of grape ripeness for hundreds of years, and many growers still rely on sugar readings to decide when to pick their grapes. Consequently, obtaining accurate sugar measurements is important. In this country, grape sugar content is measured using the Brix scale. Brix is “grams of dissolved solids in 100 grams of juice.”

Brix can be measured with either a hydrometer or an optical instrument called a refractometer. The accuracy of either instrument depends upon temperature. Most hydrometers 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. However, most modern refractometers are temperature compensated, and the compensation greatly reduces the temperature error.

Ordinary tap water can be used to check the zero point of hydrometers and refractometers. Hydrometers do not have zero adjustments. Any zero offset must be added or subtracted as each measurement is made. Most refractometers have an adjustment screw to set the zero point.

Besides calibrating the zero point, many winegrowers also use a Brix calibration solution. They make up a standard, 20-Brix solution by dissolving 100 grams of ordinary table sugar (sucrose) in 400 grams of distilled water, [100 grams / (400 + 100) grams = 20 grams / 100 grams]. This 20-Brix solution can be used to calibrate both hydrometers and refractometers, but the sugar and water must be ACCURATELY measured.

Titratable Acid (TA)
Tartaric and malic acids make up roughly 90 percent of the acid content in grapes. The amounts of tartaric acid and malic acid are about equal when grapes start to change color (veraison). The quantity of tartaric acid remains roughly constant throughout the ripening period. But, malic acid decreases as the grapes ripen, and the loss of malic acid results in a gradual decrease in the titratable acid (TA) of the juice during the ripening period.

pH
Grape acids differ in strength, and tartaric acid is stronger than malic acid. A quantity called pH is used to measure the strength of the acids, and pH uses 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. As grapes ripen, malic acid is lost. The acid content decreases, so the pH of the juice increases. Late in the ripening process potassium ions accumulate more rapidly in the juice. The potassium ions interact with acids in the grapes and cause the pH of the juice to increase more rapidly just as the grapes are reaching maturity.

OTHER HARVEST CRITERIA

Cabernet Sauvignon grapes picked at 24 Brix in one vineyard may produce high quality wine. But, Cabernet grapes grown a mile away may produce green, under ripe tasting wines when picked at 24 Brix. A third, nearby Cabernet vineyard might produce overripe, stewed-fruit tasting wines when picked at 24 Brix. Sugar content alone may not provide an adequate measure of grape maturity, so here are a few more ways a winegrower can use to judge grape ripeness.

A Clean Pedicel
When grapes are fully ripe, the pedicel (stem) can be pulled off the berry easily and little or no pulp or skin tissue will be attached to the pedicel.

Soft Berries
Berries dehydrate slightly, and the texture of the pulp softens when grapes ripen. When red grapes are fully ripe, the berries are not quite so firm when squeezed and the skin becomes slightly slack (not wrinkled like a raisin).

Red Fruit Flavors
Under-ripe red grapes often have a green, herbaceous smell and taste reminiscent of asparagus or bell peppers. Ripe grapes have less of this green, herbaceous character and more plum and cherry characteristics.

Brown Seeds
The color of grape seeds changes from green to brown as the berries ripen, but all of the seeds don’t get ripe at the same time. In most varieties, the pointed ends of the seeds (the “beaks”) are the last part to turn brown.

IN THE VINEYARD

As harvest day approaches, the winegrower goes to the vineyard every few days to inspect the vines and to check fruit maturity. He looks at the condition of the vines to see if they are strong enough to continue ripening the grapes. Then the grower walks up and down the rows. He picks grapes one by one and carefully examines each berry.

(1) He pulls the pedicel from the berry and looks to see how much pulp is attached.
(2) He checks the texture of the berries by gently squeezing them between his thumb and forefinger to see if the grapes have started to soften.
(3) The grower tastes and smells the grapes to see if the herbaceous character has diminished and the red fruit character has started to develop.
(4) The grower spits the seeds into his hand and looks to see if the seeds have changed color. Some winegrowers will NOT pick red grapes until 70 to 80 percent of the seeds are brown.

Sugar Sample Collection
Ripeness varies from grape to grape, from cluster to cluster and from vine to vine. Berries near the shoulder of a cluster will be more mature than berries near the bottom. Clusters exposed to sunlight develop faster than clusters hanging in heavy shade, so clusters from the north side of vines are generally less mature than clusters from the south side. Maturity also varies from vine to vine across a vineyard because of changes in soil conditions, water content and wind exposure. To minimize these variations, the grower collects a large sample of grapes to take to the laboratory where he measures Brix, TA and pH using standard measurement techniques. Here is a simple but effective way to collect a grape sample.

(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, be consistent and collect at least 100 grapes.
(3). Most of the sample grapes should be picked from the bottom of the clusters (watch out for bees), and be sure to pick some berries from clusters growing back under the foliage in heavy shade. (This procedure produces results that are more conservative).
(4). Seal the baggy and keep the grapes cool until the Brix, titratable acid and pH measurements can be made.

SUMMARY

Some winegrowers pick each year “when the grapes reach 24 Brix.” Other growers pick ”when the TA crosses the pH plot.” But, deciding when to pick is not easy, so contentious winegrowers use all the information available. They use Brix, TA and pH data together with their vineyard observations to decide when to pick. So, this walking about the vineyard picking, squeezing, tasting, spitting seeds and collecting sample grapes is an annual pre harvest ritual.



DECIDING WHEN TO PICK THE GRAPES IS THE MOST IMPORTANT DECISION A WINEMAKER MAKES EACH SEASON.