The Limits of Our Knowledge

March 22nd, 2008 → 1:38 pm @ Josh Hermsmeyer


This past Thursday I headed up I-80 to Davis to attend RAVE 2008. There were a number of cool presentations, but the final talk of the day by Dr. Mark Matthews was by far the most provocative.

Matthews covered a lot of ground in his talk, which was an overview of the research he had conducted on the factors relating to wine quality over the past 25 or so years.

The main theme was that a lot of the dogmas long held by researchers, enologists and viticulturists in the wine industry might be based on a poor analysis of the data.

Dogma #1: Vine Balance

For instance, winegrowers talk a lot about vine balance. Part of Matthews’ talk was designed to show that vine balance appears to be a nebulous concept of little real value since the way we measure it (comparing grape yield to the amount of dead plant matter trimmed off each vine at the end of the year) is flawed.

The acknowledged range for the ratio for crop weight to pruning weights is between 5 and 10. There have been many studies that back this up and wine literature is rife with nods toward the idea.

The problem is that when you graph pruning weight ratios along with wine sensory evaluation data, you don’t find a correlation. Instead what you find is that nearly all wine, both good and not so good, falls within the 5-10 ratio.

In other words, if as a grower you were hoping that by keeping your vine in balance you would give yourself a better chance to make good wine, you’d be wrong. Bad wine is as likely to be made as good wine.

So obviously there are other, more important factors in play. The most we could say is that a 5-10 ratio might be necessary, but not sufficient for high quality wine. There’s more to the story than just vine balance.

Dogmas #2 and #3: Berry size and Low yield

What else is thought to contribute to wine quality besides vine balance?

Lots of folks (myself included) feel berry size is another key indicator. The smaller the berry, the better.

Low yield (sometimes a byproduct of vine balance, sometimes not) is also accepted to be a driver of quality. I’m a big believer in low yields as well.

But here again it seems that the whole process is much more complicated than simply “grow small berries and limit your crop.” Here’s a cut and paste from Matthew’s lab website:

That small berries are superior to big berries, and that high yield translates into low quality, are two prevalently held dogmas within the wine industry. Data suggest that it is the journey rather than the destination that determines wine grape composition and wine sensory attributes.

We have found that the composition of the berry is more dependent on how it got to a size than on the size itself, and that what may matter more to fruit composition and wine sensory attributes than just yield per se, within a wide range of yields, are the conditions under which the fruit arrived at said yield. See the research summary figure below:



Click to enlarge

“It’s not the destination, but the journey that matters.” Interesting stuff.

Could Global Warming Be Dogma #4?

And then today I stumbled across this, from an ABC Radio interview with an Australian biologist named Jennifer Marohasy:

Duffy (the interviewer): “Is the Earth still warming?”

Marohasy (the biologist): “No, actually, there has been cooling, if you take 1998 as your point of reference. If you take 2002 as your point of reference, then temperatures have plateaued. This is certainly not what you’d expect if carbon dioxide is driving temperature because carbon dioxide levels have been increasing but temperatures have actually been coming down over the last 10 years.”

Duffy: “Is this a matter of any controversy?”

Marohasy: “Actually, no. The head of the IPCC (Intergovernmental Panel on Climate Change) has actually acknowledged it. He talks about the apparent plateau in temperatures so far this century. So he recognises that in this century, over the past eight years, temperatures have plateaued … This is not what you’d expect, as I said, because if carbon dioxide is driving temperature then you’d expect that, given carbon dioxide levels have been continuing to increase, temperatures should be going up … So (it’s) very unexpected, not something that’s being discussed. It should be being discussed, though, because it’s very significant.”

Last March I wrote about a presentation to the Napa Valley Winegrowers I attended that suggested that global warming might actually be good for Napa winegrowers. I was very surprised at the time, and I still am.

Now I hear that temps have leveled off globally or even dropped? The mind reels.

But there’s even more. From the interview:

Duffy: “Can you tell us about NASA’s Aqua satellite, because I understand some of the data we’re now getting is quite important in our understanding of how climate works?”

Marohasy: “That’s right. The satellite was only launched in 2002 and it enabled the collection of data, not just on temperature but also on cloud formation and water vapour. What all the climate models suggest is that, when you’ve got warming from additional carbon dioxide, this will result in increased water vapour, so you’re going to get a positive feedback. That’s what the models have been indicating. What this great data from the NASA Aqua satellite … (is) actually showing is just the opposite, that with a little bit of warming, weather processes are compensating, so they’re actually limiting the greenhouse effect and you’re getting a negative rather than a positive feedback.”

Duffy: “The climate is actually, in one way anyway, more robust than was assumed in the climate models?”

Marohasy: “That’s right … These findings actually aren’t being disputed by the meteorological community. They’re having trouble digesting the findings, they’re acknowledging the findings, they’re acknowledging that the data from NASA’s Aqua satellite is not how the models predict, and I think they’re about to recognise that the models really do need to be overhauled and that when they are overhauled they will probably show greatly reduced future warming projected as a consequence of carbon dioxide.”

The point of this huge spew is, I suppose, that there are huge gaps in our knowledge.

When we taste grapes in the vineyard and decide to pick, do we really know how the flavors we taste then will translate to finished wine? Or are we just guessing? Do we really know which of our vineyard practices are actually contributing to higher wine quality? Or are we just following tradition and accepted wisdom? Is the earth really on fire? Or, in our human hubris, are we underestimating the planet’s ability to adapt and survive?

On this most holy of weekends, these are some of the questions that keep me up at night.