The term 'tannin' is commonly used in wine circles, but many people aren't really sure exactly what it means. In this detailed article, Jamie Goode unpacks this important subject, and discusses some exciting new data that challenge the conventional wisdom on this topic. I’m facing the usual dilemma. I’m writing on a highly technicalaspect of wine science, for a mixed readership. I want to keep this piece interesting and understandable enough that non-technical types will stay with me, but I also want to include enough in-depth material so that hardcore wine science dudes will still find it compelling—I think it’s an achievable goal, but ultimately you will have to be the judge. Why is the subject of tannins an important one forthe wine trade at large, and not just winemakers and anoraks? I can think of two reasons. First, I suspect that whatever your involvement in the trade, you’ll be familiar with the term ‘tannin’ and it’s a word that you’ll have used frequently, perhaps, may I humbly suggest, without a clear idea of what you are referring to. Second, it’s a field of active current research, and data that are onlynow just accumulating are pointing towards a very different understanding of the role of tannins in red wines than that traditionally espoused by wine textbooks. In this feature I’ll present a brief overview of the subject and then look at the new picture that is emerging from recent research. As with many wine science topics, there’s a lot still to be learned, so much of this piece
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Tannins in wine
will concentrate on framing the key questions that still need answering. You’ll be relieved to hear that I’m going to try to focus on concepts and ideas, rather than spend too long on chemical structures and formulae. Introducing tannins The term ‘tannin’ is an old one, and comes from the practice of using extracts fromplants to cure leather (the process referred to as ‘tanning’). This process exploits one of the key properties of tannins: they have a strong tendency to link up with a range of other chemical entities, most particularly proteins. Applied to animal skins, tannins cross-link the proteins, turning something rather soft and floppy into a material that’s tough and inert enough to make shoes, belts andsaddles from. Tannins are therefore defined functionally. They are polyphenolic compounds that bind to and precipitate proteins. It’s a slightly complicated picture: not all polyphenols can act as tannins, and not all phenolics that bind proteins are tannins, but it’s still a useful definition. Now would be a good time to introduce some of the key players in this story, in an attempt to makefrighteningly chemical-sounding names understandable to a broader audience. First, we have polyphenols. These are a group of compounds that are vitally important in wine, and more specifically red wines. The name stems from the basic building block of this class of chemicals, which is the phenol group. This is a specific chemical structure that consists of a benzene ring with various additions, andit’s highly reactive. It likes to stick to other things, and an important property of phenolic compounds is that they associate spontaneously with a wide range of compounds, such as proteins and other phenolics, by means of a range of non-covalent forces (for example, hydrogen bonding and hydrophobic effects). Before we get to tannins, we need to take a look at the other group of polyphenolic compoundsthat are also key participants in this story, the anthocyanins. These are the red/blue/black pigments in grapes, which are almost always found in the skins, giving ‘red’ grapes their colour. Five different anthocyanin compounds are found in red wines, the dominant one being malvidin. We’ll come back to these later when we discuss the connection between tannins, wine quality and wine colour....