Sweet taste of some dry red wines - is Peynaud right?

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IvanV
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Sweet taste of some dry red wines - is Peynaud right?

Post by IvanV » Mon Jun 28, 2021 3:13 pm

Some dry red wines taste very sweet, although they have little or no residual sugar. Jammy, it is someties called. They are typically young red wines from hot places. I don't like them. But some of them have the concentration and structure age into wines that I do like. In such cases, the perception of excessive sweetness goes away as the flavour substances evolve.

On a wine forum I subscribe to, someone asked about the chemistry of what is going on here. Plainly there are many substances that taste sweet, completely unrelated to sugars, such very sweet such as artificial sweeteners, even some inorganic chemicals. It's rather like we established in the bitter taste thread, that numerous different substances taste bitter, although the perception of them varies considerably among individuals.

I had a look in Emil Peynaud's classic (but boring) book "The taste of wine". He suggests that by far the main chemical responsible for producing a sweet taste in wine, aside from sugar, is alcohol. But he also suggests that the perception of a sweet taste can be balanced by bitter and acid flavours. So this would suggest a simple explanation that jammy red wines are alcoholic (consistent with being warm country wines) but lacking in bitter and acid flavours to balance it. Or perhaps those bitter and acid flavours have not yet been released due to other substances.

Do you think this is an adequate explanation? Are there other chemicals in red wine that can have an important contribution to a sweet taste that Peynaud has overlooked? Do we believe his explanation for why all dry red wines of the same alcohol level don't taste equally sweet?

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shpalman
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Re: Sweet taste of some dry red wines - is Peynaud right?

Post by shpalman » Mon Jun 28, 2021 3:47 pm

Esters tend to have pleasant fruity aromas, but in general I wouldn't be surprised if fruit had evolved or been human-selected for a sweet "taste" which didn't just come from the sugar content, i.e. the fruit would be more appealing without having to just create lots of stored energy.

Compare with how much sugar you have to put in a sponge cake or biscuit something to get it to taste sweet, for example.

(Esters aren't stable enough for perfumery so a similar effect is created with the right aldehydes/ketones).
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Re: Sweet taste of some dry red wines - is Peynaud right?

Post by IvanV » Mon Jun 28, 2021 10:50 pm

A little research and I discover esters are not generally stable in the wine bottle either. They are mostly gone after a year in bottle. They contribute to the particularly fruity smell of really young wines, and are a contributor to the attractiveness of certain wines intended for very early drinking. They mainly form during fermentation, but then degrade in bottle pretty quickly. So this sweetness feature, which is certainly present in wines of rather more than a year old, indeed can take over 5 years to dissipate, is not accounted for by esters. Some esters are also markers of faults, most famously ethyl acetate is not a nice smell and is indicative of the wine being oxidised in an undesired way. A wine with an ethyl acetate fault is called "volatile" by wine tasters, which seems weird if you are used to the usual use of the word.

I'm aware that many ester formations are senstive equilibrium reactions subject to the usual chemical equilibrium concentration formulas. I'm also aware that the rate of reaction to get to equilibrium of some esters is rather slow at room temperature, and can take many years. So until today I thought that ester formation was one of the things that happened as a wine aged (in a good way, not a bad way). But apparently not. So there's something I learned today.

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Re: Sweet taste of some dry red wines - is Peynaud right?

Post by Bird on a Fire » Mon Jun 28, 2021 11:15 pm

Jancis Robinson's Oxford Companion to Wine says this:
Wines taste sweet mainly because of the the amount of RESIDUAL SUGAR they contain (although the impact of this on the palate is greatly influenced by factors such as the levels of ACIDITY, TANNINS and CARBON DIOXIDE in the wine as well as by the serving TEMPERATURE). ETHANOL, or alcohol, can also taste sweet, as can GLYCEROL and a high level of PECTINS. Any wine with less than 2 g/l residual sugar is considered bone dry, but a dry wine with residual sugar of less than 2 g/l that is relatively high in alcohol, such as many a Chardonnay for example, can taste quite sweet. A sweet VOUVRAY, on the other hand, made in a cool region from the naturally acidic grape variety CHENIN BLANC, may contain well over 30 g/l residual sugar, but in youth can taste dry.
I'm no Jancis Robinson, but I certainly think the flavour of wine (and other things) tends to come from the interaction between various flavour components, so the idea that perceived "sweetness" may depend in part on how prominent other flavours are seems reasonable.

Also interesting to note that there are other compounds that might taste sweet - pectins seem like a good bet for a jam-like flavour ;) They're also more concentrated in riper grapes, so that still fits with your "hot region" hypothesis. And then ethanol and glycerol are both fermentation products, so a higher starting concentration of sugar would still lead to a sweeter final product even if all the sugar gets converted.

Interesting stuff. I've been eyeing up Jamie Goode's The Science of Wine for a while, which might go into more detail.
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Re: Sweet taste of some dry red wines - is Peynaud right?

Post by IvanV » Tue Jun 29, 2021 10:52 am

Bird on a Fire wrote:
Mon Jun 28, 2021 11:15 pm
I've been eyeing up Jamie Goode's The Science of Wine for a while, which might go into more detail.
It seems it is variously called Wine Science and The Science of Wine in different markets, as there is a 1000-page technical book for university oenology courses that shares one of these names in the US. There is a 3rd edition out this month.

There is a table of contents of the 3rd edition available here. In 224 pages, one of 19 chapters is on flavour chemistry, which I suppose is about what we might expect given the many issues it covers. I might be tempted.
https://www.ucpress.edu/book/9780520379 ... ce-of-wine

He has written another book called I Taste Red, which is more focused on flavours. Unfortunately I can't locate a table of contents for it. https://www.ucpress.edu/book/9780520292246/i-taste-red
Jamie Goode has a blog, so maybe he has written about these things on there. I'll have to have a look some other time.
https://www.wineanorak.com/wineblog/

Meanwhile I have been researching the role of glycerol in wine. It is apparently the 3rd most abundant chemical in wine after water and ethanol, being present generally in the range of about 5g/l-10g/l in dry wines, and up to 30g/l in sweet wines. That's pretty basic, I wonder why I didn't know that. Botrytis-affected wines are especially high in glycerol. It is also higher in wines from partially dried grapes like amarone. I read a suggestion that it tends to be higher in dry red wines than dry whites. Though it is also notably high in dry white wines from Australia and South Africa, at around 10g/l in many of those. Wines like dry riesling are low in glycerol, down to about 4g/l.

Some studies seem to suggest that in these concentrations it has very little effect on the taste of dry wines. There are also indications that it does contribute some small element of sweetness. But it is not very sweet and the effect is small. So I'm not convinced glycerol is the culprit.

There is a particular class of tastes in wines, more obviously in whites where tannins are less evident, which I have learned to attribute to "fruit acids", from the time in my youth when I went to tutored tastings. These are prominent in young wines, and soften or "open up" with age. Until just now, I thought that this happened due to esterisation. Of course, if they were reacting with glycerol they would make soap. So not reacting with glycerol. And we have just learned that in general esterisation is reversing, not proceeding, as wine ages.

I clearly would like to gain a better appreciation of what is going on chemically as wine ages.

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