Physiological Maturity – Daniel Baron

Physiological Maturity


Although it is out of the sequence of the current growing season, this week I will address a more general stylistic topic – physiological maturity. One of the more fascinating aspects of the marketing of wine is the way scientific or quasi-scientific terms are thrown around to give legitimacy to whatever stylistic decisions one is trying to justify. I’ve no doubt been guilty of this myself over the years. Reading Mark Matthews excellent and provocative work, “Terroir and Other Myths of Winegrowing”, I found his extensive discussion of the term “physiological maturity” particularly revelatory. This is indeed scientific terminology, it just doesn’t mean what a winemaker implies when he says, “I didn’t pick that vineyard today because it wasn’t physiologically mature.” In fact, this is a term defined in 1984 by the American Society of Horticultural Science to differentiate maturity from ripeness in climacteric species, i.e., those that will continue to ripen after being picked. Grapes are not climacteric, so the use of this term to justify picking decisions sounds scientific, but it really is not. The choice of when to pick, alas, is more stylistic than botanical.


There has been some clarifying work of late that shows anthocyanins, the coloring molecules in red grapes, are at their maximum shortly after sugar loading slows. Sugar loading curves are obtained by tracking grams of sugar per gram of berry weight as opposed to degrees Brix, which are percent sugar in a solution. Thus when Brix goes up it could be due to import of sugar or to simple dehydration. Over 24 degrees Brix, most if not all increase is due to dehydration. Following sugar loading gives the winemaker a better feel for what is going on in the physiology of the grapevine. The point here is not to cast judgment on one decision or another but to use these detailed observations as a way to understand our successful picking calls. Ultimately, if the winemaker makes a picking decision that results in the style of wine he or she desires, then they picked at the right moment. I find this somehow liberating. No need to justify our decisions with fancy terms, it’s ripe when we say it’s ripe.


We are privileged to be part of an international community of winemakers. There is room for many different styles of expression. Each of us has our reasons for the stylistic choices we make in producing our wines. I have been making an effort of late to be accurate in my use of language, remembering that although we all have a product to sell, we are also always acting in the role of wine educators.


Daniel Baron


  1. Dan Baron has nailed it (no surprise). We should print this, laminate it and keep it handy, especially as harvest approaches.

  2. Hi,

    Do you have citations for the sugar loading/ anthocyanin peak studies. You mention recent studies, I would like to access those. thank Tim

    1. Tim,

      A good reference article on the relationship of sugar loading to anthocyanin accumulation is: Quantifying phenotypic plasticity of berry traits using an allometric-type approach: A case study on anthocyanins and sugars in berries of Cabernet Sauvignon. Sadras et al. Australian Journal of Australian Grape and Wine Research. 13, 72-80, 2007. Here is a link to the abstract:

      Thanks for your question.


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