Correspondence with Sarah/Sparky Marquis

After a heated debate on the residual sugar content of the Mollydooker '06 Maitre d', I emailed Sarah and Sparky Marquis, the winemakers/CEO's of Mollydooker Wines, asking about the exact value. They were kind enough to clarify some aspects of winemaking:

On 11/14:

Hi Rajiv,

The residual sugar on the 2006 Maitre’D Cab is 2.8g/L. Most of our 2006 reds were bottled with residual sugar levels around 3g/L and this is normal for us. If I can help you with anything else, please don’t hesitate to contact me.

Regards,


Sarah Marquis
CEO / Winemaker


On 11/15

Hi Rajiv,

Just expanding that one more step. All wines have residual sugar in at least the 2-3.5 g/l range. These are made up on unfermentable 5 Carbon sugars (normal sugar that is ferment able is a 6 carbon sugar) so in all winemaking we call anything under 3.5 g/L as being “dry” (meaning that is doesn’t have any fermentable residual sugar).

In our wines what you are seeing is fruit sweetness and structural balance. We call this “Fruit Weight”. We see Fruit Weight as being the “velvet glove” sensation of fruit on your palate before you see the structure of the wine becoming obvious.

Hope this helps

Sparky Marquis
Sarah's Husband/CEO/Winemaker


I responded on 11/15:

Hi Sparky,

Thanks so much. I had read in Alexis Lichine's Encyclopedia of Wine and Spirits that the threshold for tasting residual sugar was ~.2% (2g/L). We previously tasted Red Heads Studio's '04 "Barrel Monkeys" Shiraz, which seemed only vanishingly sweet to us, and had a residual sugar concentration of 1.1 g/L (listed on Vine St. Imports' website). Does that mean that the grapes were simply picked at a lower brix, so there were less sugars total, leaving less residual pentoses?

In any case, we were surprised by how much "sweeter" the '06 Mollydooker Cab tasted, and were curious as to how much of the impression of sweetness was due to the residual sugar, the (incredible!) amount of fruit, or other factors, like perhaps glycerine (would glycerine be higher since the alcohol content is high, and glycerol is a byproduct of fermentation?).

Sincerely,
Rajiv

P.S: Please let me know if I'm misusing any terms - I'm a chemical engineer, and I worked in a yeast genomics lab for two summers, but the wine world is relatively new and confusing to me


On 11/18:

Rajiv,

That is fantastic that you said that you are a chemical engineer as I will be able to use some of the technical terms that I tend not to use when I am normally talking about our wines.

In terms of the Cabernet, you hit the nail right on the head with your comment about glycerol. Early on in my career as winemaker, I found while studying the glycolytic pathway (the use of sugar by yeast to produce alcohol) that there was a particular side shunt to the pathway that produced glycerol. This site shunt can only be activated by the build up of NAD which is normally produced and then used in the complete glycolytic pathway.

In the latter stages of the glycolytic pathway after the glucose is broken down into 2x glyceraldehyde-3-phosphate the process is then:

1. GA3P to Acetaldehyde
2. Acetaldehyde + NAD (+ alcohol dehydrogenase) produces Alcohol + NADH2 +CO2

The NADH2 is used in the early stage of the split of Glucose to GA3P.

What we found was that if we bound the Acetaldehyde a build up of NAD occurred and that the side shunt to produce glycerol would be activated. We experimented with the use of SO2 (which is a preferential binder onto Acetaldehyde) and found that if we add SO2 to the ferment when the alcohol was being produced, that we could arrest the ferment momentarily and consequently produce glycerol. Our aim then was to produce enough glycerol to eliminate the “hole” typical in the mid palette of Cabernet. After quite some experimentation we found that adding 15ppm SO2 at each of 3%, 4% and 5% alcohol produced the amount of glycerol that we needed so that the glycerol on the palette mimics fruit sweetness. Glycerol per se, is not a natural byproduct of the production of alcohol and so 99% of other winemakers never get this benefit in their Cabernet.

Post fermentation we then work on the structural balance of the Cabernets, so that the underlying acid, alcohol and tannin (both grape and oak) compliment the palette weight produced by both the fruit and the glycerol.

Hope this helps and we look for the catching up with you soon.

Sparky Marquis
Sarah's Husband/CEO/Winemaker

On 11/19, I responded:

Hi Sparky,

Let me see if I understand this:

In the fourth stage of Glycolysis, Fructose-1,6-bisphosphate is split into G3P and dihydroxyacetone-phosphate, which is normally isomerized enzymatically into a second G3P. The next stage (phosphorylation of G3P) yields 2NADH as a by-product. At the end of glycolysis, pyruvate is decarboxylated into acetaldehyde, then fermented, using up NADH which would (if aerobic) go towards oxidative phosphorylation. If acetaldehyde is blocked by SO2, there is a buildup of NADH, which "reaches back" and makes the phosphorylation of G3P unfavorable. As a result, more dihydroxyacetone-phosphate goes down the alternate glycerol-synthesis pathway (which uses up NADH, restoring balance).

From what I could learn, glycerol production can be increased in several ways:

1. Induce a hyper-osmotic environment. - but the glucose concentration is limited by the brix at harvest.
2. Grow yeast at pH 7 or above - but again, doesn't make sense in winemaking.
3. Use special, osmo-tolerant yeast strains (because of (1), they produce more glycerol) - but this would alter many wine characteristics.
4. temporarily retard fermentation by fixing acetaldehyde with SO2 - a good solution because it doesn't mess with anything besides alcohol/sugar/glycerol concentrations.

Since both alcohol and glycerol are produced from a fixed starting glucose concentration, it seems to me at first that by producing more glycerol, you sacrifice alcohol content - a major part of the wine's "body." However a higher glycerol concentration allows the yeast greater osmotic tolerance, so if you harvest really, really high brix grapes, the SO2 will cause more glycerol production, but alcohol production will still be high. In this way you get full-bodied, 16% wines that also have enough glycerol to fill the midpalate.

So, do you harvest at a higher brix than most wineries because of your increased glycerol production?

Sincerely,
Rajiv

On 11/19

Rajiv,

Now you are talking my language.

I was going to say in the previous email: of course the usage of GA3P in the conversion to glycerol reduced the alcohol of the wine by the equivalent conversion (dependant on molecular weight ratios), but I thought that if I put this comment that I would have to go back to my chemical engineers handbook to look at the molecular weights to give you the real figures. All I can remember at the moment is that glucose is MW180 and everything else is affected by alcohol (my brain that is). Now what I do is tell our team….this is what we are doing and then we spend the rest of the time drinking rather than discussing (not really, all our team are very scientific, I spend most of my time myth busting).

And yes we pick at a higher Brix so that you get good levels of glycerol and alcohol……and much enjoyment as you drink our wines with high Fruit Weight.

PS if it was oxidative wouldn’t the process then go to the Kreb Cycle??

Sparky Marquis
Sarah's Husband/CEO/Winemaker