How mould affects the flavour of sweet wines

If you’re partial to a sweet wine, particularly one of the very best (such as Tokaji or Saiternes), it’s interesting to learn that the flavour is affected by different moulds. Ideal Wine Company discusses the research behind this.

Mould wouldn’t normally be the sort of flavour anyone’s after from their favourite drink, but scientists have pin pointed exactly how different kinds of moulds can affect the wine’s taste.

Ideal Wine Company sweet wine mould
Can mould impact the flavour of sweet wines?

Noble rot

German scientists have been studying botrytis cinereal (also known as grey mould), bunch rot and noble rot, and their effect on wine.

They’ve found, with a high degree of certainty, that noble rot increases the aromatic compounds in the wine. This produces a flavour combination that is at once floral, fruit and toasty. It’s what gives sweet white wine that delectable scent and flavour that keeps you going back for more.

Not so noble fungi

Other fungi that commonly affects vineyards includes Eryiphe necator, also known as powdery mildew. This is the kind of rot you don’t want in your grapes as it robs the vines of the vanilla flavour compounds, leaving it flat in taste and much less interesting.

The scientists tested wine made from both healthy and botrytis infected Roter Riesling, Gewurztraminer and Riesling grapes. They also used powdery-mildew infused hybrid Gm 8622-3 in their studies.

The researchers analysed and recorded specific odorants in the wine samples, and then asked a panel of ten ‘sniffers’ to rate them. These sniffers had been extensively schooled for more than six months to recognise 90 separate odours. The sniffers then rated the odours they detected.

Mouldy results

The scientists published their findings in Frontiers of Chemistry and showed that powdery mildew and noble rot both changed the composition of the aroma elements. These subtle changes ‘significantly affected’ the quality of the wine’s aroma.

It was found that grapes infected with noble rot increased the fruity smell that’s characteristic of Tokaji Aszu wines. The study also found that other lactones were also boosted, namely lactone sotolone, which has been likened to smelling of curry. On top of this they found an increase in alcohols and esters, which could account for the toasty flavour notes.

With the powdery mildew infected grapes, they found decreased levels of esters, vanillin and decanoic acid. The wine was not popular with the panel of sniffers, not due to tasting or smelling horrible, but down to the lack of interesting aroma.


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