“I have walked across the surface of the Sun. I have witnessed events so tiny and so fast they can hardly be said to have occurred at all. But you, Adrian, you’re just a man. The world’s smartest man poses no more threat to me than does its smartest termite.” – Doctor Manhattan
The above quote by Doctor Manhattan from the 2009 movie, Watchmen, made a very big impact on me. Not only did Doctor Manhattan have extraordinary physical capabilities, but also boundless intelligence and wit. Most scintillating however, was his ability to observe and control miniscule atomic particles and impossibly fast to imagine metaphysical events. Doctor Manhattan didn’t really strike me as a lush, but I’m sure that he would have been fascinated with the chemically complex and ever changing matrix that is maturing wine.
As a former minor winemaker at quite a few cellars, my favorite place has always been the barrel maturation cellar. Barrel ageing is ostensibly one of a wine’s more important stages of evolution before bottling. But how exactly does wine change during barrel ageing and what effect does it have on the countless chemical reactions taking place in wine every second? The main effect of oak barrel ageing is twofold. Wood character is introduced (the rate and intensity is mostly dependent on fill status of the barrel) and oxygen is very slowly introduced to the wine. Generally speaking, this results in softening of the harsh tannins and flavors present at the end of fermentation. Oak is a fascinating substance, which has a profound and remarkable effect on the flavor chemistry of wine. Key oak derived compounds are tannin, lignin, cellulose and hemicellulose.
Tannin plays a vital role in barrel ageing. Although most tannin in wine comes from the grapes, some of it is also liberated by the barrel during ageing. So what exactly is the deal with tannin? An experienced winemaker will instinctively know how to optimally merge and balance the tannins extracted during the youthful stages (fermentation, skin contact and pressing) and the mature stages (barrel ageing and blending). For instance, more tannic grape varieties such as Tannat, Cabernet Sauvignon, Nebbiolo and Shiraz cannot be approached the same as the less tannic Pinot noir. Once again, winemaker experience is paramount.
OK, now hold on to your chemistry hat, here comes the hard (but interesting) bit! Phenolic compounds (consisting of natural phenols and polyphenols) in wine are largely responsible for imparting taste, colour and mouthfeel to wine. They include phenolic acid, stilbenes, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). Natural phenols can be separated into flavonoids and non-flavonoids. The latter group includes stilbenoids such as resveratrol and phenolic acids such as benzoiz, caffeic and cinnamic acids. The former group includes anthocyanins and wait for it… tannins!
What would a good red wine be without vanilla flavors, sweet and toasty aromas and notes of tea and tobacco? Specific compounds create these nuances in finished wine, for example: volatile phenols containing vanillin; carbohydrate degradation products containing furfural, a component yielding a sweet and toasty aroma; “oak” lactones imparting a woody aroma; terpenes providing “tea” and “tobacco” notes, and hydrolysable tannins, which are important to the relative astringency of the wine. Take note, every time you’re quaffing a wine (hopefully a worthy vintage), you’re consuming everything you’ve just read above. If this doesn’t sit quite right with you, then I guess nothing much will.
They say you should have respect for your elders. So, tread lightly the next time you pass through a barrel maturation cellar. You might even see Doctor Manhattan skulking around in the dark, silent corners…
Bernard Mocke is a technical consultant for Oenobrands.
As discussed in previous postings, longevity may be considered within the pantheon of wine quality. The reductive strength of a wine is a measure of oxygen uptake and the ability to handle that uptake, that is improve with age. In red wines this is influenced principally by phenols and impacted by several winemaking protocols.
In a recent study (Kassas and Kennedy 2011) wines commanding the highest market value had several attributes in common including the highest concentrations of total tannins, the highest concentration of skin tannins and tannin-anthocyanin bound pigment polymers.
In grapes and wines, anthocyanin pigments can be either free monomers, that is, unbound, or associated with other compounds including phenols such as tannins to form polymers.
Tannin polymerization in fruit and wine continues until an anthocyanin molecule binds the terminal ends of the tannin chain forming ‘bookends’, thus stopping the polymerization. As such, the ratio of anthocyanins to tannins is important. This ratio impacts the extent of polymerization and, therefore, astringency.
Large tannin-tannin and tannin-anthocyanin polymers provide a relatively large number of binding sites to interact with proteins, as well as salivary proteins. As such, wines with an abundance of large polymers tend to lack softness and often possess a dry mouth sensation.
Conversely, smaller polymers have fewer protein binding sites and produce less astringency while providing a softer mouthfeel and often more palate depth. These smaller polymers are associated with enhanced reductive strength and wine aging potential.
Some phenols (diphenols) have the ability to react with oxygen, bind with another phenol, and recreate the original structure-thus allowing it to react over and over again. This helps explain the rather counter intuitive feature of exposing a young wine to oxygen and making that wine more resistant to oxidation. Young red wines can consume oxygen, actually increasing reductive strength.
Randall Grahm of Bonny Doon Vineyards in California considers reductive strength to be analogous to a wine’s chi or, as the Chinese say, life force. When a wine is young, it can share its chi with the world; when old, it must guard it so the wine does not diminish too quickly. Young wines have a capacity to adsorb oxygen and that can actually increase its resistance to later oxidation. Irrespective of chi, we believe that reductive strength is related to the phenolic composition of a wine and, therefore, to longevity.
“Experience is the name everyone give to the their mistakes” - Oscar Wilde
Dr Bruce Zoecklein is a Professor Emeritus, Enology-Grape Chemistry Group Virginia Tech.
His Enology Notes are available at www.vtwines.info.
If the title of this blog caught your eye, my ploy worked. Please accept my apologies; Flash Gordon will not be featured here. Or any other superheroes, for that matter. I will however elaborate on Flash Détente and its super colour-extraction abilities.
Of late, growing interest in colour extraction (especially in California) has led to the evolution of thermovinification into Flash-Détente. During thermovinification, the temperature of crushed red grapes is raised to 60˚C for anything from one to 24 hours. Thermophiles (pardon the pun) claim that increased tannin and colour extraction is to be had with thermovinification. The logic behind this is sound, as the high temperature breaks down cell structures. This in turn releases pigments, tannins and volatile compounds in the absence of ethanol. In the absence of alcohol, chemical bonds are formed between anthocyanin pigments and other phenols which stabilizes colour in the resulting wine. Should this concept give you cold feet, you might want to opt for cold soaking. During cold soaking, crushed grapes are soaked in their own chilly juices and pumped over for a few days in an effort to extract more colour.
Not impressed yet? Enter Flash-Détente, which is basically thermovinification on steroids. Grapes are briefly (two to five minutes) heated to 85˚C and then cooled in a vacuum. Cell walls pop, juices fly and a myriad of aroma and colour compounds are released. The vaporised water (with volatile compounds trapped within) is then chilled in a condensing column, after which the winemaker is left with the decision of adding the fluid fraction back to the main tank or not. Seeing that this condensate is full of pyrazines and in the case of lower quality grapes, rot and mold aroma compounds, the winemaker usually discards the condensate. This is however a double- edged sword, as varietal and fruity aromas is also lost in the condensate. Then again, the heat application inhibits enzymes such as polyphenol oxidase and laccase, which are often present in lower quality grapes. The effect of this heat on Brettanomyces is still ambiguous. Other benefits of extracting colour earlier are; improvement of purple hues in wine, fermentation at lower temperature and usage of different yeast strains. It is also speculated that the softer and rounder tannins are better extracted with water and heat, while the harsher tannins might be brought out where ethanol is the solvent.
Many traditional winemakers believe that Flash-Détente is for higher yield facilities, where often quantity outweighs quality (sic). It has been said that the loss of varietal character often results in a one-dimensional, soulless wine. As with all other winemaking decisions, the decision to go with or without thermovinification is an important one. Current studies on thermovinification are focusing on changing tannin concentrations in must with an increase in temperature and how varietal character is affected.
With a price-tag of $2 million for a Flash-Détente set-up, winemaker experience will be key in the decision to employ this system or not. Like they say, talk is cheap.
Bernard Mocke is a technical consultant for Oenobrands.
Now I bet very few of you have given this any thought. After all a rosé and a blanc de noir is a “white wine” made from red grapes. So you use your normal settling enzyme. However, this “white wine” contains a certain amount of anthocyanin, which means this anthocyanin should preferably remain a stable colour to ensure the longevity of the wine. In plain English, the wine should preferably remain pink or onion skin, whatever our style is, for a year or longer. It should not turn slightly brownish. In the absence of tannin from the grapes, or ellagic tannin from wood, or oxygen from micro-oxygenation, how does one stabilise this colour? Well for one; keep stuff that can de-stabilise it in the first place away from it.