By Andrew Hodson, Veritas Vineyard and Winery
Brief recap, to witness the properties of a wine we go through the same framework each time. We have covered the appearances of wine and how to adequately smell the wine and in our last few segments we have been talking about describing the tasting of wine in the same systematic way. The properties we consider when we taste wine come under the following categories
So this week our topic is tannins. Tannins are tricky, mostly because their complex chemical properties are really not well understood. Tannins in wines should be thought of as preservatives and are the determinants of wine color in red wines. White wines have tannins but nothing like the extent to which they are present in red wines. Remember in nature white grapes are the exception the vast majority of native grapes be they Labrusca or Vinifera are red.
And as a note of clarification the grapes that make red wine for the most part are black so I use the term red or black interchangeably.
I do not want to make this a chemistry lesson but what I do want to do is help you understand where tannis fit in when it comes to describing their properties as you taste your glass of Domaine Romani Conti..
Tannins are everywhere in the plant world in leaves, bark, wood and even seeds.
Wine tannins come from grape skins, stems and seeds but also when wine ages in a barrel some tannins leach from the oak itself into the wine. Winemakers have the ability to add exogenous (artificially derived tannins) according to their stylistic goals
They are called tannins because, way back when, tannins from oak bark were used in tanneries to make leather and they were used because one of their most important chemical characteristics is that they denature proteins. Tannins taste bitter and the reason why they dry up your mouth is because they denature the proteins in saliva and stop salivary flow, a property called astringency.
To grossly simplify things, think of a tannin as a substance that is built up of individual building blocks called phenols and think of a phenol like a lego building block and as the blocks link up (a process called polymerization) so their properties change going from short chain – hugely bitter and astringent to longer chain polymers that as they get older so they become less bitter and less astringent. There are two main phases we can consider as tannins mature, in the plant and in the wine.
In the plant, sunshine and when I use the word sunshine I really mean UV light, is crucial to polymerization of tannins something we always knew – sunlight ripens fruit.
But the ripening of the tannins in the grapes is only the beginning of the story, once those tannins have been extracted from the skins of the grapes into juice that is then fermented into wine the tannins continue link-up (polymerize). . For example after five years a wine will go from bitter and astringent to mellow and mouth watering.
The key to the slow process of aging is oxygen.
Oak wood barrels although watertight are not oxygen tight, oxygen is able to diffuse very gradually over periods of years through the wood pores and into the wine.Throughout that time the tannins continue to polymerise and in some case they actually precipitate into the bottom of the bottle. It is that sediment that we try to eliminate when we decant wines that are greater than five years old. Not that five years is an absolute cut off time, you can decant any wine at any time in its life span.
Anthocyanins are the pigments in red wine.
I want to now cover another tricky part and that is the relation of tannins to the color of the wine.
Red wine is red because of pigments called anthocyanins. Anthocyanins are structurally similar to tannins because they are made up with those same lego-like building blocks that we met before called – phenols that continue to change, read that as link-up or polymerase, that’s why a red wine changes color as it ages. Anthocyanins also change color with changes in the acidity of wine- the pH. As I mentioned last week anthocyanins act like litmus paper they go red when acid is high (low pH) and blue when the alkalinity is high (high pH).
In addition to color change anthocyanins affect mouthfeel, just as tannins do and help wine age, just as tannins do and as you can imagine are important in determining how long a wine will age. To quote Bruce Zoecklein emeritus professor of Enology at Virginia Tech “Tannins polmerize until they are capped on both ends by a color molecule, that stops growth… (of the tannin). Simply put color is preserved and retained in wine by bonding with tannins and vice versa what is important is the ratio of anthocyanins to tannins as to how bitterness and astringency are expressed.
The fact that oxygen causes tannins to polymerize has led in the last few decades to a technique called micro-oxygenation. Oxygen is bubbled through wine rather like oxygen being bubbled into an aquarium. Oxygen is delivered directly to the wine instead of gradually diffusing through an oak barrel. As a result the anthocyanins and tannins polymerize over infinitely shorter periods of time and to some extent enable wines to mature over months instead of years.
As a general rule black grapes that have thick skins like Tannat and Cabernet Sauvignon have high amounts of tannin and anthocyanins that with higher levels of acidity result in higher bitterness and astringency.The opposite would be grapes like Pinot Noir and Grenache that have thin skins and consequently lower levels of tannins and anthocyanins are much lighter in color and are much smoother in texture. Notice that Pinot noir the grape that is used to make sparkling wine has the lowest amount of tannin.
Although tannins are bitter and astringent we like to describe tannins in terms of how they feel in the mouth, so typically we would say the tannins feel like silk or velvet alternatively they could feel like chalk or sand paper. How tannins are percrived is dependent on multiple factors that makeup any wine be it a sparkling wine or a glass of Barolo these factors are all interdependent and the overall impression of a wine is dependent on the interplay of these factors.
How tannins are perceived depends on virtually every other component in the wine including sugar, acidity, and ethanol that are primary components that we assess as we work through our systematic approach to tasting.
In summary as I said tannins are tricky and what I have done is to take a 30,000 foot view on the main points as to how tannins work in wine tasting rather than get tied up the weeds of the complex chemistry.
Remember that tannins are always changing and that change is for the most mediated by oxygen that has similar chemistry to the red pigment anthocyanins of red wine.
Next week I am going through how we assess alcohol in wine and its role in balancing the different constituents. What is clear is that when tasting wine each individual property although independent in itself, as a dynamic of every other property/component in sparkling wine and for that matter any wine that you have the enjoyment of tasting.
Keep tuned and Keep sparkling…