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New Advances in Understanding Wine Texture

©Richard Gawel

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Last week I had a rare treat. Another chance to taste a very slurpy wine from my favourite white Burgundy vineyard 'Les Folatieres'. This beautifully complex Premier Cru Chardonnay had its usual cheessy barrel ferment complexity and subtle hazelnutty fruit. However what rang my bells was its unmistakable creamy texture that seduced my palate with every mouthful. It is this rarely encountered slipperyness that sets wines of this class apart from the thousands of other run of the mill Chardies. The same thing could be said of great red Burgundies with their velvety tannins, Barossa Shiraz with their mouth-coating richly textured mouthfeel, and Barolo with its unmistakable saliva sucking astringency.

The underlying causes of these desirable in-mouth textures takes some explaining. While it cannot be denied that the tannins leached out from grape skins and seeds is responsible for the astringent sensation in red wines, the subtleties encountered in the worlds great wines cannot be explained solely by them. In 1927 two French scientists, Semichon and Flanzy suggested that a group of naturally occurring substances in grapes called pectins were important in producing palate softness and richness. Pectins are part of a bigger group of substances called polysaccharides. The effect of wine polysaccharides on wine mouth-feel has recently been studied by Australian and French researchers based at the Australian Wine Research Institute. I had the fortune of being involved in the tastings that explored the role of polysaccharides in wine texture and was left in no doubt as to the importance of these compounds in softening and filling out the palate of wines.

There are a few different types of (impressively named) polysaccharides in wine. The first two types are formed in the grape - Arabinogalactan proteins (AGP's) and Type II Rhamnogalacturonans (RG-II's). A third group called Mannoproteins (MP's) are found in the cell walls of yeasts and are released when the cells break down after the yeast complete their fermentation and die.

So what did the polysaccharides do to the feel of the wine? After being added to a model wine, the RG II's decreased the roughness, chalkiness, and dryness on the palate, suggesting that wines with naturally high RGII levels are likely to be softer and more supple to taste. Following the addition of MP's and AGP's, their palates appeared fuller and with a lighter powdery dryness, but interestingly they had little effect on the rougher textures displayed by the wines.

The reasons as to why polysaccharides improve the textural quality of wines is speculative. However, as RGII's and AGP's have the potential to attach themselves to wine tannins they may interfere with the tannin's ability to interact with our saliva (the cause of the astringent sensation). The MP's are thought to slightly increase the viscosity of the wine, something which is known to reduce astringent dryness. Other scientific studies have shown that mannoproteins also influence the release of flavour substances from the wine when it is tasted. They appear to affect different flavours in different ways - both in terms of how much is released and how quickly it happens. So in effect the mannoproteins, and probably the other polysaccharides may be the gate keepers of flavours in wine.

Ever noticed how the most velvety red wines are nearly always highly coloured? This same study also investigated the role of red wine colour on wine texture. Red wine colour is produced from red pigments found in the skin of grapes called anthocyanins. When almost pure anthocyanin was added to a wine, it had the effect of increasing the perceived fullness of the wine. While the official tasting panel results suggested a rather subtle change to wine texture, I was personally convinced of a stronger effect. To my mind, the anthocyanins produced a clearly fuller, 'bouncier', thicker glycerol like texture. Hard to describe but decidedly pleasant.

Getting back to the real world for a moment, I'd guess that the creamy texture of the Faiveley 'Les Folatieres' (and incidentally the latest Geoff Weaver Adelaide Hills Chardonnay - a real textural cracker!) is the direct result of a concentration of mannoproteins released by the yeast both during and after barrel fermentation. However many Chardonnay wines are barrel fermented, but aren't necessarily in the same class as these two. So whatever role polysaccharides play in textural quality, it is likely that it is how they interact with other wine components that will ultimately determine the quality of their mouth-feel. However understanding this relationship, and working out how to tweak grape growing and winemaking in order to consistently produce superlative wines like these two will take a lot of doing.

Vidal, S., Francis, L., Williams, P., Kwiatkowski, M., Gawel, R., Cheynier, V. and Waters, E. (2004) The mouth-feel properties of polyshaccharides and anthocyanins in a wine like medium. Food Chemistry, 85, 519-525.