By exploring the untapped potential of wine waste, these chemical engineers have found a way to produce high-value ingredients while boosting sustainability.
Australia is a leading producer and exporter of wine, ranking fifth among the world’s largest wine producers in 2021, with an estimated export value of over $2 billion annually.
Consequently, this lucrative industry that crushes around 2 million tonnes of wine grapes per year also generates huge amounts of waste. Up to 20 per cent of this weight – including grape skins, seeds and stalks – is relegated to compost or low value products and processes such as tartaric acid extraction, ethanol production or animal feed.
“Winemaking has been defined as one of the major food-loss streams in Australian horticulture,” said Monash University chemical engineering PhD student Xueqing Liu. “This has both significant economic and environmental impacts.”
To find a better use for this “waste”, Liu and Associate Professor Victoria Haritos from Monash’s Department of Chemical and Biological Engineering collaborated with Treasury Wine Estates (TWE).
The team worked closely with Coldstream Hills, a TWE Winery in Victoria’s Yarra Valley, which primarily produces red wine favourites such as Cabernet Sauvignon, Shiraz, Merlot and Pinot Noir. Red grape marc and wine lees, solid by-products from the wine-production process, are rich in valuable anthocyanins and bioactive polyphenols such as resveratrol and quercetin, which are vital to human health.
These polyphenols provide protection against the development of cancers, cardiovascular disease, diabetes, osteoporosis and neurodegenerative diseases. Anthocyanins, meanwhile, are the pigments responsible for the colours red, purple and blue in many fruits and vegetables, have antioxidant effects and are key to the prevention of several chronic diseases.
The fate of these compounds during the winemaking process was previously unknown. However, the team sought to unlock both commercial and sustainable benefits by identifying, measuring and isolating polyphenols from wine waste throughout the winemaking process.
“Bioactive polyphenols and anthocyanins could have a number of commercial applications as functional ingredients, including in dietary supplements and as natural food colourings,” Liu said.
“We see great opportunities and are keen to explore how this waste product can be processed commercially,” Haritos added.
Analysing the winemaking process
Each winemaker has its own production process, depending on the variety and quality of grapes used. When it comes to producing red wine, however, the process typically entails slightly crushing and destemming grapes post-harvest, which are then transferred to a tank for alcoholic fermentation.
“The mixture is then pressed, producing ‘post-press wine’ which is further processed, through malolactic fermentation, sulphur dioxide treatments, maturation, blending and bottling,” Liu said.
During the alcoholic fermentation process, marc and lees are removed.
“Because there are so many different classes of polyphenols in wine and grapes, the first step was to identify the key bioactive polyphenols,” she said. “So we set up a few selection criteria including polyphenyl concentration in grapes and wines, antioxidant activity and clinical data.”
Next, the team investigated what happens to these polyphenols during the commercial winemaking process.
“We visited Coldstream Hills to investigate the partitioning of those key bioactive polyphenols using a mass balance approach.”
The team’s mass balance equation tested the notion that polyphenol concentration in grapes could be accounted for by the sum of the downstream products – wine, plus lees and marc.
“We collected commercial samples from each stage of the winemaking process, then analysed and measured the polyphenols in those samples,” Liu said.
This allowed the team to identify that during the fermentation process, polyphenols are either transferred from grapes into wine and lees, or remain with marc during this step, with quercetin found to be the most prevalent compound. Non-soluble in wine, there were significant amounts of this polyphenol in marc and lees.
“Based on the whole commercial winemaking process, alcoholic fermentation is the key step to extract the polyphenol from grapes in both wine and waste, with large amounts remaining in waste,” Liu said.
Turning water into wine
With untreated marc samples collected after the fermentation process, the team headed back to the lab to freeze-dry the by-products in preparation for solvent extraction.
While bioactive polyphenol extraction from the grape marc is only at a laboratory level, Liu plans to scale up her research to commercial heights.
“Extracted bioactive polyphenols could be commercialised in powder, extract or concentrated solution form and used in different applications such as food additives, pharmaceuticals, cosmetics or dietary supplements,” Liu said.
For example grape-seed extract, high in polyphenols, is a highly popular dietary supplement, produced by several vitamin giants.
In the next phase of her research, Liu will further investigate commercial-grade processes for extracting the bioactive compounds and their potential uses, including the development of a non-alcoholic beverage.
“By valorising winemaking waste into high-value products, wineries can both make a profit, and reduce waste and greenhouse gas emissions,” she said.