The History and Evolution of Moss Wood Cabernet Sauvignon: 1999 Trellis Changes and Wild Yeast Fermentation

Things settled down somewhat for the 1998/99 growing season, with mild springtime conditions, followed by a mild summer and a later harvest. The first Cabernet Sauvignon fruit wasn’t picked until 31st March and at that point, ripeness was still a little below what we wanted. Fortunately, Mother Nature was in a cooperative mood and the first two weeks of April were fine and warm and we were able to wait and re-start, finishing just before significant rain on the 15th.

Despite being mild, the season produced fruit aromas, quite different from similar years in the past, like 1982 and 1987. This we put down to the introduction of the Henry trellis and the improved leaf and bunch exposure that results.  The tannin structure was also very well balanced.

We also instituted a major change in the winery with the use of wild yeast fermentations. We had done some experiments with these for several years prior and decided to use the technique across all wines.  In brief, indigenous yeast ferments contribute two main components to a wine.

The first is higher levels of glycerol, which improve mouthfeel, although, amusingly, we later learned this is largely imperceivable in wines above 12% alcohol, making it almost irrelevant in all the Moss Wood wines. The second component is aromatic yeast-derived complexity, which appears as mushroom and truffle notes in the background of the nose.

There are also significant risks to using this technique. The first is that an unknown yeast may produce unwanted “off” characters, like high volatile acidity, amongst others. Secondly, since the population of the yeast is unknown and potentially quite small, it may struggle to complete the fermentation, leading to further quality problems.

Given that we only have one opportunity to make wine each year, these risks are significant because we don’t want to ruin any batches at this crucial stage.

When tasting the different wines from 1999, they all display interesting nuances on the nose, confirming the activity of wild yeasts. In particular, the Semillon is notably different from previous vintages, although still in a style typical of Moss Wood.

The Cabernet Sauvignon shows this to a lesser extent but also has higher volatile acidity than normal, but fortunately, it is not intrusive.