What is tannin?
Tannin is the name given to a range of complex molecules found in wine that don’t have a smell or taste, but affect the texture of the wine in your mouth. Tannins in wine can come from different sources, such as the naturally occurring tannin in grapes known as a proanthocyanidin. Interestingly this type of tannin is closely related to red wine colour, the main component being anthocyanin – a flavonoid pigment found in plants.
In a ‘good’ year, when the yield is low, the flavour, colour and tannin are generally more intense. These traits are desirable and considered indicators of wine quality. Of course, in some circumstances high tannin may not be desirable, but this is usually due to a specific choice of wine style.
Where does tannin come from?
Tannin can be found in a variety of foods and beverages, such as dark chocolate, cranberries, pomegranates and tea. It’s also found in some nuts and many types of wood. The tannin in wine comes primarily from two sources: grapes and oak barrels. The skins of many classic grape varieties such as Shiraz (Syrah), Cabernet Sauvignon and Merlot contain tannin and anthocyanin, while the pulp (flesh) is essentially colourless. Tannin can also be found in the seeds, but the type and structure are different to those found in the skins. Generally, seed tannins are nuttier and can be bitter.
During red wine fermentation, the grape skins and seeds are fermented in contact with the juice and pulp. Heat and alcohol produced during fermentation help extract the tannins, which end up in the resulting wine. Once fermentation is complete, the grape skins are ‘pressed’ (squeezed) to extract the remaining wine and tannin.
At this point, the wine may contain quite a high level of tannin produced naturally from the fruit. Typically, the wine will be transferred into oak barrels for maturation. Oakwood naturally contains another group of tannins called ellagic tannins, which add to the existing tannin in the wine. As well as tannin, oak barrels impart other texture and flavour compounds into the wine.
What does tannin do to wine?
Without tannin, red wine production would not have begun thousands of years ago. Tannin is a natural anti-oxidant and one of the key ingredients that can prevent red wine from spoiling. To make a ‘stable’ wine product (a wine that will last for 6 months +), there cannot be any fermentable compounds (namely sugar and malic acid) or oxygen left in the wine to allow microorganisms to grow. Selected yeast and bacteria take care of the sugar and malic acid, which is important for wine stability. A typical alcohol of 14%v/v, makes it difficult for many microorganisms to survive. However, if oxygen is readily available then certain microorganisms can very quickly turn wine into vinegar, or worse.
This is where tannin comes in. As a good anti-oxidant, it will scavenge oxygen until all of the available tannins have reacted with it. If the wine is in a closed container (a barrel or bottle), this process means oxygen will no longer be readily available for spoilage organisms to use and grow. If you read my previous post on ageing wine, you’ll also discover the importance of acidity and the preservative Sulphur Dioxide in red wine stability.
Tannin in modern winemaking
While tannin plays a technical role in wine stability, it’s contribution to the ‘mouth feel’ (texture), of the wine is also important. Our understanding of wine stability, combined with improvements to packaging, means we can take a different approach to working with tannin. It’s contribution to wine stability has become less important and the texture of the wine more so.
Different winemaking techniques can influence the effect of tannin, such as ferment temperature, time in contact with the skins, cap management, press type and oak treatment. We can produce full flavoured wines with great colour and softer tannins aimed at earlier drinking; or we can produce more traditional, high tannin wines designed to age for many years.
Tannin can also be purchased from wine industry suppliers. Various types are available, some extracted from grape marc (skins after pressing), some from different types of wood and nuts, and the top end is extracted from oak. These products may be used to re-balance the mouthfeel and structure as required. Only the use of nut-based tannin needs to be indicated on the label due to allergen labelling laws.
When we taste wine, along with all of the smells and flavours that can usually be related back to some kind of herb, spice, fruit or other weird references (barnyard, cats pee, etc!) there are also textures to describe. Tannin is responsible for quite a bit of the texture response when we drink wine. This is because tannin reacts with protein, particularly the saliva in the mouth, making it less slippery. The type and amount of tannin will vary the texture and overall ‘mouth feel’ of the wine. Tannin can be expressed using descriptors such as chalky, dusty, silky and velvety, just to name a few.
The post image I have used is the ‘Mouthfeel Wheel’ from GAWEL, R. , OBERHOLSTER, A. and FRANCIS, I. L. (2000), A ‘Mouth‐feel Wheel’: terminology for communicating the mouth‐feel characteristics of red wine. Australian Journal of Grape and Wine Research, 6: 203-207
It’s a tremendously useful resource I use often when describing wine for tasting notes etc.
Once again, in my previous post on ageing, I described tannin as having a significant role in the longevity of red wine. During the maturation process, very small amounts of oxygen find their way into the barrel, then into the bottle. Unless the barrel or bottle seal is compromised, the amount of oxygen is not great enough to cause spoilage. It does, however, react with the tannins in the wine. When tannin is young, the tannin molecule is short and the tannin may be described as being ‘hard’ or ‘grippy’, astringent (mouth puckering) and drying. Small amounts of oxygen cause the tannin molecules to polymerise (join together) and become larger. These larger molecules feel softer (silky or velvety), less astringent and more agreeable, which is one of the reasons for maturation.
Tannin and the Rusty Mutt reds
Coming from a more traditional wine-making background, tannin has been critical for the longevity of my wines. Maturation in the barrel, then bottle, both before and after release, is needed to make the tannins softer. However, these days far less wine tends to be bought for cellaring, so I’ve taken a different approach towards tannin in the Rusty Mutt reds. Using gentle cap management (hand plunging) and basket pressing (a very gentle press method) I aim to make full flavoured wines with mid to soft tannins. My wines are designed for drinkability on release, but the type and amount of tannin are balanced with the other stabilising factors, producing a wine with mid-range cellaring potential. Both the Rusty Mutt Shiraz and GSM will drink well right now and continue to grow in complexity with optimum drinking around 5-8 years from vintage.
After all, wine is made to drink, so I don’t want you to wait too long before drinking and enjoying my wines!