I want to find out if tannins are a source of colour in whisky. You would think that there would be plenty of information out there, but to be honest, I have found very very little information about the colour of whisky in whisky science books.

Books such as “Whisky, Production, Technology and Marketing” do identify that tannins are a source of taste to the whisky, but no to very little links are made to the colour of whisky. Some of these tannins degrade as the barrel is charred.

What are tannins?

I have found multiple definitions of what tannins are.

“A tannin (or tannoid) is an astringent, polyphenolic biomolecule that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids.” ~ Wikipedia

“Tannins are a loosely defined group of water soluble plant polyphenols, characterized by their ability to bind proteins.“ ~ Haslam, E. Plant Polyphenols: Vegetable Tannins Revisited. Cam- bridge University Press (1981).

One of the stuffs that makes your tea colour is a tannin. It is in the leaves of the tea. It is in black tea, green tea. You name it and there are tannins in tea. Notice how I use “Tannins” and not some kind of very specific “2,3, trans-blabla-ic acid”. Which tannin is in which tea I don’t know, but we all made tea and one can see how fast a teabag gives colour and flavour to tea.

Also notice how Ralfy makes reverence to the astringency of a “breakfast tea” note in some whisky. “Now you know, just charing” ~ Ralfy.

The stuff that makes red wine red is a tannin. It is in the skin of the red grapes and to a lesser extend in the white grapes. Just google “tannins in red wine” and be amazed how many hits you get.

red grapes with green leaves on the vine
Photo by Ashley Field (CC) : https://www.flickr.com/photos/138570099@N03/

The stuff that makes your fishtank turn brown when you put a branch of driftwood in … you guessed it .. a tannin.

The stuff that makes a stream of water turn brown when full of leaves. Again, tannins.

For some very very odd reason the fishtank world knows where the colour of a brown fishtank water comes from. The wine world knows where the colour of red wine comes from. The tea world can explain it in a nanosecond. But for whisky scientists the origins of whisky colour is a big mistery? Sounds to odd to be true correct?

So which tannins might be in whisky? Well that is where the whisky science books help out. Other books that help out are “Wine Tasting, a professional handbook” by Robert S Jackson.

Jackson details a list of Grape, Oak and Yeast origins for “Phenolic and Related” compounds. See table 4.2 in the second edition. He also lists the colour imparting effects of a number of compounds.  Table 2.2 in the same book lists a number of colours of polyphenols and tannins combinations. I cannot copy this information without permission, but colours differ from colourless, to yellow, to red to violet.

In “Wine Science, principles and applications” Jackson descibes in detail the colour formation processes. Dependencies on pH values are described. Other dependencies also are detailed in detail. Pages long of fun chemistry that detail complex interactions and reactions between molecules. All resulting in colours and shades of colour.

Many whisky and wine maturation congeners come from the oak wood. Some of them are hydrolysable tannins. Some of these tannins have colour. Some other compounds have colour too. Let’s stick with tannins for now.

Wine, any wine, that matures in oak casks extracts water soluable tannins from the oak. They combine, react, etc, with the tannins in liquid extracted from the grapes. The concentration of these tannins are “even” trueout the wine. So the wine that is “absorbed” in the wood also contains the same level of tannins. Tannins from the grapes are also absorbed in the oak.

Sherry is a wine. PX sherry is a wine. Oloroso sherry is a wine.

Ergo, the tannins in the grapes that make it into the sherry also make it into the barrel of the cask holding the sherry. Therefor the “Sherry cask” holds Oak, Grape and Yiest originated tannins. Three sources of tannins.

Ones emptied and reused for whisky, these “three-source-tannins” want to move into the water and ethanol of the whisky in order create an equalibrium of concentrations. This will mean that some of the “Grape and Yeast” originated tannins  in the original wine/sherry will make it into the whisky. It may be that the alcohols (notice I say alcohols, not ethanols) in whisky want to react with these tannins and quite possibly change them of break them down, but some will “make it”.

Red wine grapes Tannins make red wine red. Makes sence doesnt it. This explains, at least partly, why “sherry” matured whisky is redish.

When I wrote “what the phenols” I did not know this stuff about “tannins”. I will remember that “phenols”, “polyphenols” and “tannins” are part of the same family of chemicals.

Now I also understand why the “ppm” of a peated whisky is measured on the kernels of the barley and not on the finished spirits.

This blog also helps me identify the more astringent dry notes on the Revised Scottish Whisky Flavour Wheel.

I havent made a list of tannins in whisky yet. but I am sure I will add it to this blog in the near future and also link PubChem pages as reverence.