Fruit variability, or unevenness in fruit quality from any given vineyard, is something that is probably not considered seriously enough by most grape growers and many winemakers. Yet variability is the "norm" in the natural world (pun intended), and we winegrowers either attempt to minimize it, to manage it, or we ignore its existence or its importance entirely.

I think that it's a fair statement that if you ignore variability in the grape, your wine will tend towards mediocrity. There are huge volumes of mediocre wine out there, and there is a tremendous market for that wine. However, international competition has been encroaching on that mid-priced wine market, and winegrowers need to pay closer attention to the cream of their crop and how to prevent blending it in with the lesser fruit from their vineyards.

Winemakers, driven to produce a higher quality product, are justified in wanting more uniformly ripe and uniformly composed fruit at their crush pad. That does not come without cost, however, and the cooperative winegrower needs to be compensated for the extra measures.

Variability of What?

Firstly, we must all agree that great wine can only come from great grapes. (If you don't buy that, then don't bother to read on.) Winemakers choose to buy grapes from vineyards that deliver the characteristics they need to produce the style and quality of wine that they are targeting.

We generally speak of physical (berry size, seed hardness, skin integrity, etc.), biological (i.e., disease) and chemical (sugar, acidity, pH, tannin, anthocyanin, flavor, aroma precursors, etc.) components of the grape when specifying fruit quality, but we cannot possibly control each and every component of the grape when we grow it.

Rather, we work within the topographical, climatic, soil and weather limitations that each vineyard and vintage provides us to achieve the targeted flavor, aroma and mouthfeel qualities in our wines. Winemakers—and, increasingly, winegrowers—know optimal ripeness when tasting fruit in their vineyards. Reducing ripeness to physical and chemical components is necessary for technical discussions, such as this one, but are not really what ripeness is all about. Our goal (for rising above mediocrity) should be to deliver fruit to the winery that is of similar ripeness and full flavor potential, from the top of the bin to the bottom, from the first bin to the last.

In conversations on the subject, I've noticed that we are often confused in talking about variability in fruit quality versus variability in fruit ripeness. Ripeness is just one of the factors (although inarguably the most important) that influence fruit quality and its variability.

There are numerous factors in any vineyard that can limit the potential fruit quality, regardless of how ripe the fruit is. For instance, a Cabernet Sauvignon vineyard that has swales and ridges will likely have more spring growth in the swales than on the ridges, leading to a denser canopy. Fruit from the swales will most likely have larger berries, less flavor intensity and have more vegetative character (due to methoxypyrazines) than fruit from the ridges. Even if the time of ripeness is evened up in that vineyard, there will be different styles and/or qualities in the fruit that is harvested from those respective regions.

But it often does come down to uniformity of ripeness. In assessing ripeness, we are often awaiting an "absence of negatives" in the fruit flavor, which often means waiting for the veggie, green characters to go away. We are fooling ourselves if we must wait for lagging fruit to ripen (or become non-veggie) while the already-ripe fruit in that same block shrivels before we can pick it.

Variability in ripeness can begin as early as budbreak when shoots do not emerge simultaneously throughout a vineyard. However, it is more common to witness differences in timing of bloom and fruit set within a vineyard, which carries through to differences in timing of veraison and, thence, ripeness.

Sources of Variability

Variability in fruit composition and ripening occurs over a multitude of scales. Recently, the most commonly studied scale of variation is that over an entire vineyard block.

Rob Bramley, of CSIRO in Australia, has been studying vineyard variability and applying precision viticulture techniques to manage it. He has, for instance, measured Brix values at the same time within a single vineyard ranging from 20 to 25 Brix by making well over 100 measurements, each within 11- and 18-acre vineyards. Over a four year period, he observed a variation from the median value of 15 to 25 percent in Brix values. While substantial, that was small in comparison to other berry constituents like anthocyanins and phenolics, which varied about 100 percent from their median values! Clearly, the vineyards he was observing, which are not atypical in my experience, will produce both good and bad flavors that will all blend together in the fermentation vessel.

It is not yet practical to measure fruit composition spatially throughout a vineyard, so simpler and less costly techniques need to be employed to divide a block into zones, or sub-blocks, that can be harvested separately. One method is to use aerial imagery or other canopy density mapping technology to determine dense and less dense vegetation regions of the vineyard. I have previously observed that vegetation index throughout a vineyard correlated positively with fruit acidity (i.e., higher vegetation index = higher TA) but did not correlate with Brix. One might also expect fruit veggie character to correlate with canopy density as well as other important fruit attributes, but I don't believe that those correlations have been investigated to date.

Dr. Bramley found that by segmenting blocks into two harvest zones based on yield maps, Brix was not different between the two zones, but other constituents (berry weight, TA, pH, color and phenolics) were significantly different from one another. That suggests that the two regions would produce different wines at the same sugar ripeness. In fact, this technique has been used successfully by wineries in the U.S. and Australia to segregate fruit into higher and lower wine programs.

Technology is not absolutely necessary to determine sub-blocks (but it sure makes it easier). A winegrower and winemaker can, over time, develop a sense of where the early and later ripening portions (or veggie and non-veggie portions, etc.) are in a vineyard. I understand that more and more winemakers are pushing for separate harvests of vineyard blocks. I think that, in the interest of greater product quality, there should be cooperation among the winegrowers to support this practice. In return, wineries need to be prepared to compensate the grower for the additional costs involved with doing so.

On a smaller scale than the vineyard block, differences in ripeness and/or fruit composition can occur within a vine. Vine size and spacing can have an impact on the uniformity of fruit development. I have observed greater variation in cluster Brix in cane-pruned versus spur-pruned vines that were of large size. I would not say that cane-pruned vines are always more variable than spur-pruned vines, unless the canes are long and numerous enough (per vine) to cause uneven budbreak, uneven shoot lengths or blind bud conditions. Shorter canes do not exhibit the differential timing of budbreak that longer canes do. Similarly, fruit development can differ along very long cordons. Consequently, smaller vine size will generally allow for more evenness of ripening in either cane or cordon systems.

Within a vine, variability is exacerbated in split-canopy systems, either horizontally or vertically divided. Without question, split canopies, like the Geneva Double Curtain, Lyre and Scott Henry, have their place in viticulture, being suited for sites that promote vigorous vines when other practices (e.g., irrigation, cover crop, rootstock) are not sufficient to restrain vine growth.

However, it must be realized that the two fruit zones will not ripen simultaneously nor will they necessarily have the same characteristics at ripeness. For vertically split systems (e.g., the Scott Henry), the lower fruit zone is closer to the ground and is, therefore, developing in a warmer environment. (Yes, it's warmer near the ground during the daytime.) Also, the downward-positioned shoots are less vigorous than their upward-positioned counterparts and will have less leaf area as a result.

On the other hand, in horizontally split systems, the two fruit zones will have different diurnal environments as the sun passes overhead and illuminates the fruit zones at different times of the day and for different durations. I have measured up to six Brix difference between fruit zones in horizontally split systems. I think that some of the differences can be minimized with proper row orientation and trellis design, but the potential for difference in fruit quality or ripeness should be kept in mind and differential harvesting of trellis sides may be employed to maximize quality from these vineyards.

Beyond any systematic differences in ripeness due to cordon/cane length or division of fruiting zone, there will always be random variation in any biological system. This will be most evident during veraison (for red grapes). Veraison is the one time of the growing season that we have the visual cues that provide the opportunity to drop clusters that lag behind others in their onset of ripening. This practice improves the uniformity of ripeness and of fruit character at harvest. I have also heard of growers who drop the clusters that color up first so as to allow the remaining clusters to ripen more simultaneously. That practice seems to be a bit more risky than the green drop as it will force a delayed harvest and a gamble with the weather gods.

On the smallest scale, we need look no further than the cluster to find substantial variability of ripeness. Yes, it's rather frustrating that even when we minimize or manage variability across the vineyard and within the vine, we're still stuck with variability within the lowly cluster.

There have been several studies that looked at variability of Brix and berry weight within a cluster. A 1975 study by Kasimatis et al. found standard deviations of between two to three Brix within clusters, with Brix values varying over a 10-Brix range. Now, that was with Thompson Seedless. In a recent study with a more noble wine variety (Cabernet Sauvignon), it was found that Brix varied with a standard deviation of only 0.9, which is much less than that which was found in the Thompson Seedless study. That is encouraging news, but realizing that less-ripe berries of Cabernet Sauvignon (and similar varieties) have a higher pronounced veggie component, and that methoxypyrazines are detectible in extremely low concentrations, we must still consider within-cluster variability important for high-end wine production.

I have seen ultra-premium wine producers remove individual green or pink berries from clusters at about 80 percent veraison. A pricey manipulation? Yes. But so are their wines. wbm