Tackling the 2019 MW Exam Part 1: Are yield restrictions necessary to produce high-quality wine?

Fruit thinning, green harvest, restricted yield, whichever name it may go by there are few canards as distinctly pervasive as yield restriction. Across Europe, the belief that yield restriction is directly correlated with amplified wine ‘quality’ is so widely held that one can almost predict the nature of questioning at any tasting, visit or seminar. Let’s stop for a second; just how accurate is this belief? Is yield restriction really a fundamental requirement of high-quality wine production or is this hypothesis flawed?

In this series of posts I will attempt to tackle a range of questions from the recently released 2019 stage 1 MW exam. I will tackle these questions in a somewhat relaxed manner, a manner in which I hope I will not only be able to develop my own understanding but also add value to the journey of my readers. Let it be said, I’m no Master of Wine. As such please do not expect a ‘winning answer’ Instead I will try my best to dissect each topic with rational and reason, providing both an answer and a learning resource.

In tackling this question there are three underlying assumptions which one should attempt to validate in order to achieve a binary answer. The first is to acknowledge that if the answer to this question were to be yes, it would suggest by default, that yield restriction is a one size fits all solution to improving quality, regardless of region or variety etc. The second would be that were the answer to be yes, no wine produced without intentional yield restriction could be of ‘high quality’ The third, and final, conundrum, is the challenge of defining exactly what it means to be a ‘high-quality wine’

The most common technique associated with the range of viticulture practises centred around restricting yield is green harvest (although yield restriction is not its primary purpose) An additional method utilised to some extent in restricting yield is vine training; however, when discussing viticultural yield restriction it tends to be green harvest which is the most common method employed.

Having emerged roughly in the last 30 years, green harvesting as a quality-centric viticulture technique is a relatively recent practise, but remains one which has grown exponentially in popularity. The practise emerged out of little more than anecdotal postulation, with the science remaining unclear at best. It is important at this point to differentiate between fruit thinning as a means of vine health management and as a method of purposefully restricting yield with the aim of improving quality. Fundamentally the assumption is that as a result of increased leaf to fruit ratio (principally the leaf provides sugar to the vine through photosynthesis) when one restricts yield (by reducing the number of bunches on the vine) the rate of sugar accumulation is increased in the fruit that remains.

There are a number of stylistic qualities commonly associated with wines which have undergone a programme of yield restriction in the vineyard. These are higher alcohol levels, darker colour, riper fruit character, less greenness, less acid, altered tannic structure and more concentration. However; is this always the goal and are these qualities defining variables of ‘high quality’ across all varieties and styles?

If we consider fruity, high acid wines, like rosés or of varieties such as Sauvignon Blanc, Chardonnay (in this respect as a component of sparkling wines in particular) Riesling or Grüner Veltliner etc. are we particularly looking for less acid? darker colours? higher alcohol and increased phenolic development? White grapes are fundamentally very different to red grapes, in their case a larger yield has the ability to slow ripening, thus allowing more time for green characters to dissipate and for ripe characters to develop. Additionally, in the case of warm regions positioned at the extremities of wine production, it is important that the vine has a large enough crop to sufficiently distribute the inherently larger accumulation of sugar.

In addition to the above, vine age is a further variable which one would need to consider when determining whether or not to restrict yield. A young, vigorous vine which is not yet well established to its terroir may require yield restriction whereas a 20 year old vine, already well-adapted and self-regulating may not, assuming the answer to this question were yes we would restrict both yields, potentially unnecessarily as one may achieve balance naturally whilst one might not. Considering the question within this context it seems more suitable to suggest that opposed to being presented as a universal determinant of producing ‘high-quality wine’ yield restriction be seen as a tool which can be employed dependant upon the variety, age and desired stylistic charecteristic of the wine.

The second point of contention; can a wine be considered ‘high quality’ if it has not undergone yield restriction? Having previously noted that the use of green harvest (with the intention of restricting yield) is a fairly recent phenomenon, it defies logic to suggest that wines which have not undergone this process can not be considered high quality, especially considering the esteem in which many wines predating the popularity of the process are held. Taking in to account specific producers there is a wealth of evidence available to suggest that high-quality wines are indeed produced without yield restriction. By any metric, Nyetimber is one of Englands best sparkling wine producers. Brad Greatrix, winemaker at Nyetimber, states that it is his personal experience that the quality of their wines actually increases proportionally to yield, and as a result green harvest is not typical at Nyetimber.

Finally, semantically defining high quality is of particular difficulty. If high quality is to be defined as the financial value achieved for sold wine then W. Blake Grey has shown through statistical analysis that with a range of high-end Napa Valley wines there is a positive relationship (R = 0.22) between yield and secondary market prices meaning that wines from higher yield years are actually likely to cost more. A perhaps more appropriate measure of high quality is structural balance and critical acclaim, metrics which are measured and attributed somewhat simultaneously through critic scoring and awards. Making further reference to Nyetimber, it is evident that where green harvest is not typical, a wine remains able to achieve both balance and critical acclaim.

To summarise, based on the aforementioned I do not believe it to be true that yield restrictions are necessary in order to produce high-quality wine. Not only does it appear evident that the result of direct yield restriction is more closely related to desired style opposed to quality, it appears more appropriate that it be viewed as a tool, a tool which is employed dependant on a range of variables such as region, variety, vintage yield variation, vine age, desired style, climate, terroir and clonal vigour variation. Furthermore, it seems to me somewhat one-dimensional and ill-fitting with the diversity of varying wine style to suggest that a single, relatively new, practise should be a universal defining factor in producing high-quality wine.

11 thoughts

  1. Interesting idea of yours and good read.

    The following observation of an ex vigneron. They are not scientific just the result of casual experimentation and observation over 17 years.

    Vines that are well established and in equilibrium with their site (well pruned, proper site location etc) seem to be able to compensate no matter the crop size and year – they generally ripen their grapes. If you have worked towards finding this equilibrium over say 10 years, you find the crop starts to level out year on year in any case. I’m talking about vines of minimum 20 years of age.

    This is not always the case with young vines and vines planted in areas better suited to growing asparagus – vines that are for one reason or another, too exuberant or too well nourished. Young vines may need fruit dropped for their own long term good. Young vines may well ripen a large crop (sugar wise) but it can take a lot out of them in the ensuing years and lead to a repetitive (and self defeating from a quality point of view) cycle of ‘nourishing’.

    Thats my bit.

    PS Vines in a dry place e.g. Corbieres and in equilibrium with their site will regularly produce on average 35 hl/ha per anum in my experience. In rare years that may touch 45.

    1. Thank you so much for the comprehensive reply Pat, I hope you don’t mind but I have added this point (briefly) in to the post as an edit. Interestingly Brad, from Nyetimber, mentioned that one of the occasions where they will employ green harvest is when restricting the yield of vigorous young vines, so your experience rings true with their work.

  2. Don’t forget that the training of the vine is also a limit on yields. Training style and cane length will determine the number of potential bunches, long before green harvest. In AOC these factors are often prescribed.

    It is also worth remembering that as vines age, their yield naturally decreases. Old vines are also synonymous with quality, so it may be that as vines age, active yield restriction becomes unnecessary, yet still produce high-quality juice.

    1. Great contribution Daryl, thank you for taking the time to read and respond. Entirely agree with you regarding training of the vine. I believe this to be dependant on the varietal and region, in some regions they do not use vine training to restrict yield, yet still produce ‘high-quality’ wine, therefore restricting yield is not essential, right?

      I think I could produce another post, not related to answering this question directly, which covers yield-restriction more comprehensively as a concept and not whether it is essential for high-quality wine. What do you reckon, good idea?

  3. There are other aspects to crop reduction which help to improve the quality of a wine. Removing 2nd and 3rd bunches evens up ripening and allows more air and light into the canopy which will reduce diseases, especially botrytis. In marginal climates (eg the UK) reducing yield down to one bunch per shoot will both reduce crop, increase sugars and lower acid levels, helping improve quality with otherwise hard-to-ripen varieties such as Pinot noir and Chardonnay for still wine (but not sparkling). In my experience, young vines will carry the crop they are happy to ripen and normally they don’t suffer from an early yield. But then I come from a region with normally good levels of growing season rainfall which of course has an impact on the health of young vines.

    One of the enigmas of viticulture is that often the weather conditions that give you a big crop are ideal for ripening a big crop, whereas the weather conditions that give you a small crop are those that are also bad for ripening any level of crop. Low cropping Bordeaux years are often the worst for quality for example. You also didn’t mention that crop reduction may be an appellation measure, designed to reduce the amount of wine available for sale.

    Stephen Skelton MW
    PS You said “I am under no illusion that I am no Master of Wine” – surely one “no” too many?

    1. Stephen, thank you for taking the time to reply, I appreciate it.

      Totally agree with everything you’ve said; my understanding is that this forms part of what is common vineyard ‘health management’ so to speak? Interestingly two others have said they have found in their experience their young vines did require green harvest, I suppose this highlights the diversity of viticulture and the impact of various other factors (as you have mentioned)

      Another good point about appellation measure. I suppose my take on the question is that it is asking whether or not yield-restriction necessary to produce high-quality wine, so I’ve approached it from the perspective of whether it is or not, it seems to me that the answer is no, high-quality wine can be produced without yield-restriction, in many cases it is necessary but not as a general rule.

      It appears from feedback so far there are many methods employed in the vineyard (dependant on region) which are geared toward even ripening and providing balance, it’s a topic I’d like to cover in a post discussing this specific matter opposed to answering the question directly.

      Again, thank you for your input Stephen, it’s greatly appreciated.

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