28 October 2005
In yesterday’s Business Day, Michael Fridjhon made use of his weekly column to report on the use of commercial yeasts. He correctly makes the point that all commercial yeasts are naturally occurring; it’s just that these are isolated and then commercialised. The benefit is that they remove the risk of bacterial spoilage while the winemaker is waiting for the wild yeasts to start working.

We only use commercial yeasts at Cloof. The main reason for this is that we need yeasts that are tolerant of alcohol levels around 14% (at a certain level the yeast gets killed by the alcohol which has been produced as a result of its life cycle). It’s not that we set out to make high alcohol wines; we harvest fully ripe fruit, which in our case means a minimum of 14% alcohol.

The other benefit of commercial yeasts is that various yeasts get the same grapes to deliver slightly different flavours. So, we use a Rhône-valley yeast on our Shiraz and a Bordeaux yeast for Cabernet. We think we get more complexity this way.

No discussion on yeast, though, is complete without commenting on the theoretically scientific conversion rate of sugar to alcohol. The last thing we need at Cloof is more alcohol than we’ve bargained on. Yet, every year we get at least one tank where the yeast has been overly efficient, delivering 15% alcohol from juice that should have ended at 13%. Yeast manufacturers take no responsibility, nor are they able to offer any explanation.

In correcting the misconception that commercial yeasts are genetically modified, Mr Fridjhon could well have raised the question: Would we accept genetically modified yeasts if we knew that we’d get lower alcohol wines? We’re not saying we’d use them at Cloof, but given market demand for full flavour, AND low alcohol, it becomes an interesting debate