© Wikimedia/Fotolia/Anna Carew |
Winemakers wanting greater depth of color and more intense aromas may soon have a new tool.While most connoisseurs wouldn't admit to having zapped their wine in the microwave for a few seconds, it's a common trick for that too-cold glass of red. Now, microwave technology is shifting from the kitchen to the winery, with some impressive results.
The sexily titled "controlled phenolic release" process, or CPR, is an extraction technique that microwaves the grape skins and juice (the must) to 70°C (158°F). Winemakers can then decide how long they wish to keep the must at 70°C before starting the fermentation.
The longer the hold time, the greater the depth of color and tannin level – which means that winemakers effectively have the opportunity to dial in a particular color and tannin level for the wine style they want to achieve.
This process reduces the length of the traditional maceration process. What might have taken up to a month with, for example, a cold soak, fermentation, and a post-fermentation maceration, can now take less than a week. This could relieve pressure on wineries that are short on tanks or when a harvest is particularly compressed. If it's a year when the berries are pale, microwaving the must may encourage the grapes to yield more color.
Achieving greater intensity
Early trials using pinot noir show that microwaved wines which were pressed off their skins prior to fermentation had similar color and tannin levels to wines fermented on skins.
What's more, pinot noir that was microwaved then fermented without skin contact created wines that had notably high levels of the varietal's signature aroma compounds – responsible for the red-cherry, chocolate and black-cherry characters in a wine.
Dr. Anna Carew, a wine researcher at the Tasmanian Institute of Agriculture, is working on further developments in collaboration with the Australian Wine Research Institute. She explains that microwaving must is a gentle form of extraction. In order to liberate color and tannins, grapes need to be opened up, damaged, or broken down in some way.
“It’s all about controlled damage” Carew said, pointing out that crushing berries is damage, as is macerating the skins in alcohol.
At present, the researchers are using a domestic microwave oven to carry out their experiments. "We microwave one kilogram of must at a time in one-minute blasts until we get to 70°C," explained Carew. "At full power, it takes around four minutes."
From kitchen to cellar
When the research moves into its next stage, the team will use a commercial microwave oven at the CSIRO institute in Victoria that can handle around 200 kilograms of must per hour. "That's not on an industrial scale either,'" said Carew, "but we're still at the early stages."
What is clear is that the microwave technique “offers control to winemakers," allowing them to decide on the time they wish to keep the must at 70°C. This pre-fermentation extraction could also be beneficial in reducing potential tannins, as they are only soluble in alcohol. If the maceration takes place before alcohol is produced, this reduces the risk of creating a wine with harsh tannins.
Says Carew: “Extended [post-fermentation] maceration adds risk in red winemaking. With pinot noir, the risk is too much bitter seed tannin. This needs to be managed very carefully or you can get an astringent, unbalanced wine.”
The other benefit of the new process is reducing any risk of spoilage. "This temperature is also effective in sanitizing the must, sterilizing the background yeast and bacteria,” explains Carew. As a result, the winemaker can control the fermentation without worrying that a rogue yeast will take over or that there could be any bacterial infection.
Heating grape juice and wine to increase extraction is not new: thermo-vinification has long been popular in eastern Europe. Heating the crushed mixture to 60–75°C (140–158°F) for 20 to 30 minutes before fermentation gives intense color but risks producing cooked flavors.
Carew believes that microwave heating is different from this more traditional heating method, due to a "greater level of disruption" of the components that hold on to the tannins and color. In addition, it provides greater extraction compared to thermo-vinification.
Researchers compared a batch of wine that was microwaved and left in contact with the skins during the fermentation, with a parcel of pinot noir that was microwaved and then fermented off skins. The differences in their aromatic make-up were remarkable. According to Carew, “14 out of the 16 aroma compounds which we examined were significantly higher in the off-skins treatment.”
Commercial trials are scheduled to take place over the next three years. Until then, the preliminary results suggest that in the future, microwaves could produce wine "with good mouthfeel and decent length."