18 August 2000 'Designer grapes' path to competitive insurance for wine industry

More knowledge about how vineyard management affects grape composition is essential if the New Zealand wine industry is to remain competitive, says Lincoln University wine scientist Dr Glen Creasy.

With more and more wine production aimed at meeting particular consumer preferences and niche market demands, vineyard managers must deliver grapes that will meet winemakers' requirements as closely as possible, Dr Creasy told participants in Lincoln University's recent Grape and Wine School.

"The most common grape composition guidelines currently used to determine suitability for wine production are the measures of berry juice sugar, titratable acids and pH.

"These parameters, easily measured and objective, influence to a large extent the price paid for grapes.

"Increasingly, however, major wine companies are starting to include other parameters in their paying schedules, using information gathered from the vineyard prior to harvest.

"This is an attempt to link what happens in the vineyard more closely with wine quality, but it does not actually measure what is in the grapes. It assumes there are certain viticultural practices which will result in grape composition that will lead to higher quality wine."

Dr Creasy says that while all wine scientists acknowledge there are other components in grapes equally important, or even more so, than sugar, acid and pH, and while these can be altered in the must or juice, it is not so easy to increase things like colour insufficiency, or to alter the flavour from, say herbaceous to fruity, in the winery.

"In essence then, we have but a handful of parameters that are easy to measure and while they tell us important information they do not give the whole picture."

Dr Creasy says that wine scientists would love to be able to quantify sensory aspects such as appearance, aromas and flavours and while the ability to do this objectively is making some progress "the road is a rocky one".

He says that while there is, in general, a dearth of knowledge in the area of fine-tuning grape composition through viticultural manipulation, there are examples of areas where it is known that grapes can be "managed" towards specific, winery specified goals.

Examples of areas open to some such "fine-tuning" are alcohol, colour, acidity/pH, flavours/aromas and mouthfeel.

"Since the amount of sugar in the juice is the major determinant of wine alcohol, actions in the vineyard that will enhance sugar accumulation, such as limiting crop load and optimising light interception, will enhance wine alcohol percentage," he said.

With colour, Dr Creasy said that past research had shown that shaded berries ended up with poorer colour at harvest than exposed berries – "hence fruit exposure and the state of the canopy are important to good colour."

He goes on to say, however, that exposure changes more than just the colour compounds and this is an example of the sort of thing that makes vineyard manipulation such a difficult process.

"Specific knowledge of how vineyard manipulation can affect a single compound is great, but what other aspects of grape composition are being altered at the same time, and how does an altered level of that compound interact with the hundreds of others in the juice and then through the winemaking and ageing processes?

"Wine is an immensely complex beverage. Until we can say how the components of the juice affect wine quality we have a moving target and thus will have difficulty in delivering the right types of grapes to the winery."

Dr Creasy told the Grape and Wine School that while the New Zealand wine industry held promise for the future there was "hard work" ahead in order to retain the country's enviable position in the world marketplace.