Article on vine yield vs. quality (long)

I saw this article by Dr. Richard Smart (credentials at the end of the article) in the new issue of Wine Business Monthly and thought it was interesting and provocative.

Tom S

"THE PREDOMINANT MYTH Surely the predominant myth of the wine industry is that high yields result in low wine quality-it is the basis of European mythology that has become legislated under appellation schemes. And these ideas are also widespread in the wine industry of the New World.

Imagine the opening of a new T-shirt shop. The grand opening is fast approaching, and suddenly the owner takes a third of the stock and throws it in the trash can. Why do this? Consider the idea that reducing overall stock will make the remaining stock more desirable to customers, perhaps giving an impression of exclusiveness and higher quality. You will surely say, "How stupid is that?" Yet for those of you out there who thin crop on your grapevines, how much factual basis do you have that discarding a proportion of the fruit will make the remainder better? Who are you trying to convince? Do you rely on a belief system?

This idea has so much currency that I have heard some grape growers "reverse boasting" about how much fruit they put on the vineyard floor. Enologists, almost universally, believe that high yields will lead to reduced wine quality. But, is it true?

If it is true, we must concede that we are part of an inefficient sector, forever destined to low productivity. The other side of the coin is even more economically distasteful: that we are discarding some of our production in the mistaken belief that this will improve quality, for which we will be rewarded.

For what other foods and beverages do we hold the same viewpoint? None, so far as I can see. Who drinks beer only from low-yielding barley or hops? Who demands steak from malnourished, skinny animals? Which wine critic at dinner will ask for small potatoes? Why are grapevines singled out for a stressful life among plants and animals, on which our agriculture is based? Because of mythology, that is why.

WHY DOES THE MYTH EXIST? I have observed in many wine regions that low-vigor vineyards have the best reputation for quality (this is admittedly more common for red than white table wines). In some instances, especially in Europe, these vineyard estates produce distinctive wines in most seasons, leading us to the conclusion that this feature has much to do with the site and less to do with the seasonal weather.

Low vigor vineyards have several common features throughout the world. Water stress is the common cause of reduced vigor. Shoot growth is inhibited, typically showing before bloom. Internodes are not so long nor diameter so wide, and main leaves are less than normal. Lateral shoots develop poorly if at all. The canopy is typically open, with good leaf and fruit exposure. Shoot tip growth slows before veraison, and growth terminates soon after. Provided stress levels are not high, the vines will produce a moderate yield that will ripen before that of high vigor vines.

Note clearly that I am not arguing for maximum stress, which will cause substantial reductions in. yield and loss of active leaf area. I am describing the typical course of developing water stress that is found in Mediterranean climates, with no or limited irrigation. Soil depth and water-holding capacity are all important.

Is low yield the cause of the quality benefits? Or maybe it is a vigor effect. Perhaps the patterns of shoot growth are also important. And the open canopy can be a contributor as well. I believe all of these points are important, and I find it regrettable that the myth has been built up to consider yield solely.

QUESTIONING THE MYTH There are many examples that suggest that higher yields do not necessarily lead to lower quality. The first I'd like to mention relates to a recent Napa Valley study involving Cabernet Sauvignon ("Sensory attributes of Cabernet Sauvignon wines made from vines with different crop yield" by D. Chapman, M. Mathews and J. Guinard, 2004, Am. I. Enol. Vitie., 55: 325-334).

Vines planted in 1995 and grafted to 110R were pruned to six levels, with between 12 and 48 buds per vine, spaced at 1.8 meters in the row. Yield was also varied by thinning at veraison to 12 to 96 clusters per vine, in conjunction with two pruning levels (24 and 48 buds per vine).

The field trials and fermentations were properly replicated, and a sensory panel trained. As was expected, yield increased as more buds were left at pruning and with less thinning, producing a range of yields varying from 1.6 to 8.8 tons per acre. The treatments produced wines that differed in aroma and taste attributes. Wines produced by pruning level showed much more effect of treatment than did those produced by thinning.

Interestingly, and counterintuitively (and certainly contrary to the myth under discussion), the low yielding vines, due to severe pruning, produced more negative wine characters than did high yielding wine. In particular, fruity aromas were higher as the number of buds per vine and yield increased. Similarly, low yielding wines were more astringent. Conversely, low yields were associated with more "veggie" and bell pepper aromas. Also interesting was the response to cluster thinning. There were no associations between aroma and yield although low yields were again more astringent.

So, low yielding wines were of "lower quality", being more astringent and more veggie but only when yield differences were established by pruning. Cluster thinning had little effect on aroma attributes despite having a greater effect on yield. However, it was important to note that the effects on wine sensory evaluation were much less than those on yield.

What is patently obvious is that this excellent study was flawed by lack of vineyard measurement. There were no assessments of pruning weight, mean cane weight or of canopy microclimate. So the authors were left in a quandary to explain their results. My guess is that the severe pruning stimulated vegetative growth and methoxypyrazine production (a cause of veggie characters).

There is no doubt, however, that yield was not the determinant of wine sensory features. Method of yield control was more important than final yield in affecting sensory features. And, significantly, higher yielding vines produced wines with more positive attributes and fewer negative ones. So much for the myth.

The second experience relates to a Cabernet Franc experiment that I conducted in Hamilton, New Zealand in the 1980s (see "Canopy management to improve grape yield and wine quality principles and practices", Smart, R. et al. S. Afr. I. Enol. Vitie., 11,3-17).

This location has a cool climate similar to northern Oregon: the soil was quite deep and fertile, and summer rainfall was significant. Vines on 1202C and AxR1 were vigorous and trained to a range of training systems, with two row spacings at six feet and 12 feet. Again, the trial was replicated as was the winemaking from each plot and the sensory evaluation. Local winemakers were used for sensory evaluation, but they were screened (without their knowledge) as to their ability to reliably assess the wines.

Vertical shoot positioning (VSP) training produced shaded canopies and lower yields, which is no surprise. (VSP is not suited to high capacity soils and high vigor. Both yield and quality can be inhibited by shaded canopies.) Other trellis treatments created a greater canopy surface area and a less shaded canopy, and so yield was also increased. When yield was compared to a wine's sensory score, a positive correlation was found. That is, the higher the yield the better the wine as assessed by wine judges. This was because the shading of the high vigor, lower yielding VSP vines reduced the color and aroma of wines. This was improved by better balanced, higher yielding vines trained to a more appropriate trellis. So much for the myth.

The third experience has to do with the 2005 harvest at Tamar Ridge Vineyards in Tasmania, Australia. We used aerial infrared photography (NDVI, Normalized Difference Vegetation Index) to create vigor maps of the vineyard. We found part of our Sauvignon Blanc vineyard to be of substantially lower vigor due to water and nitrogen stress. The yield was lower as would be expected, but we also found that the fruit at the point of harvest lacked varietal definition. Nearby, adjacent vines in deeper soil were more vigorous, with higher yield but more typical flavor. We differentially harvested the block, and the higher yielding portion produced the better wine quality as assessed at the post vintage tasting.

Consequently, Tamar Ridge has recently out pointed many well known brands from Australia and New Zealand, and has been awarded one of only two gold medals at the 2005 Perth Wine Show for its 2005 Sauvignon Blanc. This winning wine was made from high vigor vines, using differential harvesting as described above.

These are just a few examples among many to suggest that higher yields do not necessarily lead to lower quality; in fact, the converse might be true. They suggest that the means of regulating crop pruning compared to cluster thinning could be more important than yield itself. If you are cluster thinning at veraison, you should worry that you might be throwing money away. So much for the myth."

Dr. Richard Smart, the "flying vine-doctor", is an Australian viticulture consultant, with clients in 22 countries worldwide. He is an expert on canopy and other vineyard management to improve wine quality. He conducts seminars and educational wine tours to regions around the world. Dr. Smart visits North America frequently for consulting and may be contacted at vinedoctor@ compuserve.com. For more information, visit

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Tom S
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I don't know whether the predominant thinking about yield and quality is true or not, but the snip above is not any kind of parallel. That's more like throwing half your wine away to make the rest more valuable (something that does work for collectable coins).

The idea is that pruning lets the remaining grapes have a better chance at the nutrients and such that make them good. I can't really imagine T-shirts having this quality (and if they did, I wouldn't want to wear them!) Perhaps more in line with the topic would be throwing out the bottom half of your ink, because that's where the sludge is. The T-shirts made with the top half would be higher quality. Or somesuch.

Uh.... how about the trend for baby vegetables and veal? Not quite the same, but not so different either.

Jose

Reply to
Jose

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