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New World Wine Maker Blog - tannins

A List of Details

 

I’ve often said “There are only two processes to winemaking. Flavours are created in the vineyard and extracted in the winery. The rest is only details”.

Every time someone speaks of a great new winemaking process such as cold maceration or délestage, it’s time to ask yourself “Is this consistent with the style of wine I want to make?” Will this improve my process or handicap it? Will this create a greater risk of something going wrong? Break the process down into its individual elements and consider the effect of each element on flavour development. For example, a prefermentation cold soak selectively extracts water soluble compounds whereas extended post fermentation contact selectively extracts alcohol soluble components. The influence of aeration is affected by the stage at which it occurs. An early aeration can oxidize tannins and diminish their solubility whereas later stage aeration will diminish tannin astringency but may contribute to bitterness.

In some ways there is less flexibility during white grape extraction, so winemaking is more affected by grape flavours. If you wish to suppress flavour extraction, for example when working with over ripe grapes whose cellular structure has begun to break down, then you may resort to a whole cluster press. This occurs when making the typical big alcoholic Chardonnays that are left to hang until the berry begins to become flaccid. If the typical destemming were used, then tannin extraction would be a problem. This style of winemaking typically occurs at an elevated pH and runs the risk of developing bitterness in the presence of higher tannin extraction. Whole cluster pressing is also used when making a sparkling cuvée. The first, gentle press will have very little tannin extraction and is considered to be the premium part of the cuvée. Each subsequent pressing will have higher tannin content and should be kept separate, and perhaps treated with isinglass or gelatin to precipitate the tannins.

 When working with aromatic grape varieties the strategy is completely different. In this case the objective is usually to maximize flavour extraction. There is a hierarchy of aggressiveness that can be used. The most common technique is to simply run the berries through a destemmer and then press. The aggressiveness of pressing and the thoroughness of crushed berries affect the level of extraction. Flavour extraction is also affected by berry pH and sulfite. A more aggressive extraction can be carried out by using cold maceration prior to pressing. A convenient timing for cold maceration is to destem and crush in the afternoon and press the next morning. Again, the amount of air contact and presence of sulfite affect flavour. If tannin extraction is expected to be a problem, then a small amount of gelatin or isinglass can be dispensed into the crushed berries after destemming. An even more aggressive extraction of white berries can be made by adding pectinase during maceration. In this case it is highly recommended that gelatine or isinglass be added during the maceration. Tannins will tie up pectinase and inactivate it.

With aromatic varieties much of the aroma is often present as non volatile terpenes. These compounds can only be detected by the nose after they are converted to the volatile form. Many yeast contain a beta glucosidase that can carry out this reaction, but if you’re wanting more aroma, you can buy the pure enzyme preparation from suppliers.

The way in which you extract berries can also affect the stability of the resultant wine and its eventual sulfite requirement. Pre fermentation oxygen contact causes browning, especially noticeable in white wines. This results in wine that has a lower bound sulfite and is more heat stable without treatment. The down side is that you may also diminish varietal character if your oxidation is too aggressive.

I haven’t touched on the ways in which a vineyard can be manipulated to develop flavours nor have I suggested ways of blending different varieties. I’ve heard it said that if an identical batch of grapes were split among a dozen winemakers, they would still produce a dozen different wines. Even winemakers with the same training eventually develop a preferred pattern that results in recognizable differences. The potential process variations are essentially infinite. Every time the winemaker touches the process he leaves his fingerprint.

 Gary Strachan is an expert consultant and planner for the grape and wine industry. He can be reached at gestrachan@alum.mit.edu

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A glimpse at the complexity of barrel ageing

“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.

 

 

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What’s in the bag?

The cat is out of the bag so to speak. It seems that not all tannins are created equal and quality differences between suppliers exist. Best you make sure you buy from a trusted supplier…

I recently read an interesting (also from a date of publication point of view) article, published in a reputable scientific journal called: “Impact of exogenous tannin additions on wine chemistry and wine sensory character.” They analyzed the effects of a range of enological tannins in Merlot wine. First they analyzed how much of the product sold as tannin was indeed tannin. They found it to be “12 – 48%.” What is the rest of the stuff in the bag that you are adding to your wine??? They found that adding the recommended dosage of the supplier was too little to have a “measurable effect.” They then proceeded to add higher concentrations and concentrations exceeding the supplier’s recommendations. The latter did indeed have a measurable effect on the wine’s phenolic content but also had a “subsequent negative impact on wine sensory character.”

In case I misinterpreted the article, for which I then profusely apologize to all tannin suppliers, here is the link:

http://www.sciencedirect.com/science/article/pii/S0308814611013781

Your thoughts….

Karien O’Kennedy is the Online Communications Manager for Oenobrands. She also knows the odd thing or two about winemaking and fermentation.

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