Don't miss the marc: phenolic-free glycosides from white grape marc increase flavour of wine

Background and Aims: Grape glycosides are an important source of wine flavour, especially for ‘floral’ cultivars. This study tested whether phenol-free glycosides from marc could be a latent source of flavour in white wine without affecting bitterness. Methods and Results: Glycosides were extracted from Gewürztraminer marc with water followed by a polymeric resin adsorption and purification step, which removed phenolic substances. The glycosides were added at single and double the concentration of that in the grapes to Riesling and Chardonnay juices prior to fermentation, and to wines at bottling. The addition of phenolic-free glycosides significantly increased the concentration of monoterpenes and monoterpene glycosides, resulting in an increase in fruity and floral aroma, flavour and aftertaste attributes, as determined by sensory descriptive analysis, while not significantly altering the bitterness or astringency. The timing of the addition had only a minor effect. Consumer liking data on a subset of the wines indicated that a double addition of glycosides was not well accepted, although a cluster of consumers liked the Riesling with a single addition of glycosides. Conclusions: Phenol-free glycosides extracted from marc can increase floral and fruity flavour in Riesling and Chardonnay wines, without altering bitterness or astringency. Significance of the Study: Adding phenol-free glycosides from grape marc can enhance wine flavour and persistence. The relatively simple extraction method allows utilisation of marc as a source of flavour at a production scale.