Winemakers may want to consider a new tool to join their stainless steel tanks, oak vats and clay amphorae—a microwave. Recent trials at the University of Tasmania involved heating Pinot Noir grapes in a home microwave to explore the benefits of consistent heating before fermentation. The research found several unintended benefits: Grapes heated in the microwave allowed the researchers to thoroughly but gently extract tannins and color compounds during fermentation, which may make it attractive to winemakers.
For her experiments, Dr. Anna Carew made wine on a scale small enough to make garagistes look like bulk producers. She collected Pinot Noir grapes from a Northern Tasmania vineyard and separated them into 2 kilogram batches. Using an off-the-shelf, 1150-watt Sharp microwave (not unlike the model tasked with reheating leftovers in your kitchen), she and her team microwaved the batches at varying intervals of one to two minutes. Each lot reached a peak temperature of 158° F and stayed at that temperature for 10 minutes via a thermal blanket, before being cooled to 86° F. The grapes were then transferred to French press coffee makers (think of them as mini submerged-cap fermentors) for fermentation. The wine was then aged for 18 months in small glass bottles, with regular tests.
Carew discovered that microwaving the grapes led to a shorter fermentation, which reduces the risk of microbial problems. But despite the quicker pace, color and tannins were higher in the microwaved grape wines. Some winemakers have long used the practice of applying heat to the maceration process to enhance extraction, but at the risk of introducing cooked aromatics and flavors to their wines. But a microwave generates heat at a cellular level through atomic excitement rather than applying external heat. That creates a more efficient release of tannins, phenolics and anthocyanins—the goods winemakers want to extract from the skins.
Plant cell walls are susceptible to failure when microwaves are applied—a bad thing for those who want crisp cooked veggies, but a good thing for winemakers wanting to extract as much as they can from skins without bitter flavors. Carew said microwaving appeared to be a gentle way to extract color and flavors, but she cautioned that it's early for châteaus to run out and buy cellar microwaves. "At this stage, there is a great deal we've still to learn about why the process works, what happens when we use it on varieties other than Pinot Noir, and how it might be harnessed to consistently make top-quality wine," she told Wine Spectator.
“This is a novel processing idea for wine grapes," said Andrew Waterhouse, professor of enology at University of California at Davis. “I think this has real potential, but the extent of adoption will depend on two key variables: cost and flavor impact." Waterhouse believes it could be a smart alternative to flash détente, a process where grapes are quickly heated to about 180º F and then shifted into a vacuum chamber, where they are cooled. "Flash détente, which has similar attributes, has found a home in the winemaker's toolkit, but it is a niche player because the cost is relatively high, but more important, the sensory impact is not universally positive, and bitter or harsh tannins often result."