Fraser from the Relative Space team recently made an unlikely connection while on a scenic drive through France and Italy. He was visiting a wine bar in Beaune, France where he met the head wine-maker of a nearby winery. When Fraser mentioned his job – selling wood flooring – the conversation turned to tannin, a naturally occurring polyphenol found in plants, seeds, bark, wood, leaves, and fruit skins (including grapes). Fraser told the winemaker how manipulating the tannins in wood can cause a colour change in wood, which is sometimes employed in artisanal floors. The winemaker noted how the tannins in wood also play an important role in imparting flavour to certain wines via the barrels they are aged in. The pair laughed about how they were both selling tannins, one for the eyes and one for the tongue.

A Matter of Taste
In wine, tannin is a textural element that makes wine taste dry and astringent, specifically in the middle of the tongue and front part of the mouth. It comes from either the wine grapes, the wood of an oak barrel, or both. Red wine is higher in tannins because of prolonged contact with the grape skins during ageing. One example, the famous Italian Barolo, takes its extra tannic quality from the Nebbiolo grape, giving it a bold and unique flavour.

Why Oak?
The beginning of the love story between wine and oak is rather unromantic: Barrels were a simple and efficient way to ship wine. But over the centuries, winemakers realized that the tannins in the oak barrels were giving each wine a distinct flavour profile, and indeed the tannins are what set apart many of the finest wines in the world (the top fifty most expensive wines are oak-aged in some way).

To break it down a little further, oak tannins contain specific flavour compounds that are absorbed by the wine as it ages. The type of oak, whether French (from $850 all the way to $4,000 per barrel), American (strong and rugged in flavour, used more often for whiskey barrels than for wine) or Eastern European, means different flavours come to the front, and each type of wood is complementary to different wines.
An oak barrel does not have unlimited supplies of these compounds, and a barrel will stop flavouring the wine after two to three uses. After that point, the barrel is considered “neutral,” but can stay in use for many more years (wine barrels have been known to last more than a century).

Quantifying Tannins

Tannin is present in all woods, but the amount of tannin can be determined by the colour of the wood: The browner a wood, the more tannins there are. There are more tannins in the heartwood of a tree than the sapwood, which is what makes heartwood darker. Here at Relative Space, we are interested in tannins as a means of colouring wood planks that has a very different effect than a typical stain. Staining evens out the colour of a floor, but changing tannins will retain colour variation (an essential characteristic of “natural” looking floors) as the amount of tannins will vary from board to board.

A Chemical Reaction

We think affecting tannins is a much better way to change the colour of wood than staining, as the colour will be throughout the wood, which means if you scratch your floor, the colour stays the same. Sapwood’s natural low-tannin state also has an interesting aesthetic benefit; its tendency not to react to most processes creates dramatic light streaks on the edge of boards.

Unplanned tannin reactions can create problems. If you’ve ever seen a black ring on a piece of wood flooring, that was likely caused by a chemical reaction between the tannins and the floor, often caused by a vinegar spill (it turns oak black). Often, these stains are surrounded by scuff marks made from desperately trying to scrub the stain out, which is impossible.

Appealing Effects

Smoked Oak is the most common form of tannin-treated wood. There are several ways to make it, but the most common is to put the wood in an ammonia bath at a set temperature for a period of time. Smoked Ash is another common one. Theoretically, you can “smoke” any wood, but the results won’t always be attractive. For the wood nerds out there, please note there is no relationship between the appearance of tannin-modified woods and Shou Sugi Ban (Japanese fire treatment).

Tannins are sometimes added to wood to create more dramatic effects, and they are sometimes reduced or removed to make the wood more controllable. For example, decorative driftwood in aquariums needs to be leached of its tannins for the sake of the tank’s pH balance. Generally, the tannin altering processes should always be done at a factory. Site applications cannot achieve the same depth of colour penetration, and there are safety concerns.

If you would like to explore tannin-altered flooring for your project, a Relative Space consultant can show you all the interesting possibilities.

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