Fire that barrel!

I am sitting now with a glass of Chenin blanc, one eye on my two young boys trying to kill each other in the garden with their plastic bikes and the other on the barbeque fire. I am going to braai some traditional South African sosaties which will go well with the Chenin methinks! This made me think a bit further, fire can actually play a role in wine making. What you might wonder, he probably had one glass too many…

However a fire burning in or close to the vineyard can influence the taste of wine. A few years ago in Stellenbosh we had big problems with fires around harvest time. When vegetation burn close to vineyards the smoke ends up in the vines, with certain smoke derived compounds coming into contact with the berries. The two main compounds involved here are guaiacol and 4-methyl guaiacol, they belong to a group called volatile phenols. It is thought that some of these compounds go into the waxy layer on top of the skins of the berries as well as being taken up by the berries itself. Part of these so-called volatile phenols can also be bound to sugars, such as glucose, in the berry. The form bound to glucose s is actually less volatile than the free form and we thus do not really perceive the form bound to glucose. During fermentation these off aromas can then end up in the wine. They thus seem to play a larger role in red wines than whites, as one do not normally ferment white wines in contact with the skins as is the case with red wine making. These wines made from smoke infected vines then end up having an off smoke taint which basically is reminiscent of an old ash tray. It is also advised that winemakers do not give too long skin contact when making wines with these grapes, as well as do not use glucosidase enzymes, as these enzymes can break the bond between the volatile phenol and the sugar, thereby making them more volatile and easier to smell.

barrel toasting

Barrel being toasted over an open fire

The other place where fire can play a role in winemaking is when barrels are produced. After the barrel has been assembled from individual staves, the cooper can toasts it using gas, hot air or over an open fire. During toasting compounds called lignins in the wood are transformed into other more volatile and aromatic flavour compounds. This process actually warrants another separate blog post, which I’ll write at a later stage, but basically a number of positive aroma compounds are formed during toasting.  These include vanillin (vanilla aroma), guaiacol (low intensity of smoky, which contribute positively when present at low levels), lactones (oak aroma) and eugenol (clove aroma). However, the toasting should be done uniformly, if the wood is heated too fast blisters can actually form on the surface of the wood, in which spoilage bacteria or yeast can grow over time. Fire can thus indirectly decreases or increase the quality of wine.

Ok, the coals are ready, my two boys are still alive, hungry and I need to start braaing. Fire and wine, a typical South African combination, don’t you think…

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