Better – But Not Sweeter – Winegrapes

Winegrape researcher Mark Krasnow has done a lot of work on the phenomenon of berry shrivel.

We caught up with Krasnow, who is now a senior lecturer at the Eastern Institute of Technology in Napier, New Zealand, during the recent holiday season when he returned to visit his former lab at the University of California-Davis. While doing research, Krasnow said he sometimes comes across results that don’t fit with the rest of a given project, and therefore this research never sees the light of day. He had such an experience while doing work on berry shrivel. However, he thinks those in the winegrape industry should know about these particular results, because they can make for better wine.

Krasnow did an experiment in winemaking. He took normal, healthy Cabernet Sauvignon grapes and made wine from them. Then he made another batch in which 5% to 10% of the fruit had sugar accumulation disorder (SAD). “The results were really surprising; the wine that had more of the added SAD fruit was fruitier,” he said. “(SAD fruit) tastes bad in the vineyard, but it might be beneficial to leave in for fermentation in small amounts.”

While this experiment didn’t fit with his other research, Krasnow believes he has an explanation. The SAD fruit might have had much less sugar than normal fruit, but it was much higher in norisoprenoids. These aroma compounds have floral-honey aromas that can contribute greatly to the enjoyment of a glass of wine. Krasnow says norisoprenoids enhance the fruity notes in wines even if they are at lower than normally detectable sensory levels, and they suppress vegetative aromas.

It’s important to note that just as all types of berry shrivel aren’t alike, not all shriveled grapes are higher in norisoprenoids. So it is important to differentiate SAD fruit from, say, bunchstem necrosis fruit.

Krasnow can’t explain why SAD grapes are higher in norisoprenoids. “But if I were a Cabernet Sauvignon winemaker in California, I would absolutely want to know that,” he says. “It’s really weird, but it was definitely there. It needs more study, and I will be looking for SAD in New Zealand to see if I can repeat it down there.”