Generally speaking, agricultural activities and transformation processes have an important environmental impact, because of the inputs required such as energy and water consumption, and the outputs produced such as waste products and polluted water.
The wine industry is a great example of an agricultural process that generates a large amount of waste and by-products from winery activities. These include grape pomace (skins, seeds, and stems representing on average of about 60% of the total winemaking by-products), wine lees (25%), and wastewater rich in organic compounds, which represent a challenging waste disposal problem for the winery.
Traditionally, grape pomace has attracted the most attention out of the waste by-product, while wine lees have received much less attention.
Wine lees are the residue that forms at the bottom of the vessel containing wine after fermentation, other treatments, and storage.
Microorganisms are the main part of this matrix (mainly dead yeasts), while organic molecules such as tartaric acid, and inorganic matter make up a lesser part of it.
Wine lees could be exploited to obtain cell wall mannoproteins and β-glucans with several potential applications.
The vast majority of wine lees are collected and distilled or processed in order to obtain different products such as vinegar .
For this reason, wine lees, despite being the second most important wine waste by-product, has been the least studied and most underused one in the wine industry.
Fortunately, in the last few years, there has been an increasing interest in studying other applications of this waste by-product.
As a result, numerous wine lees recovery and valorization strategies linked to the circular economy principles and environmental sustainability have been proposed.
Most of these strategies are based on the high nutritional value of the components of the lees with the potential to be exploited in different sectors such as the food, winemaking, biotechnological and pharmaceutical industries.
For example, the extraction of polyphenols, in high concentration in wine lees, could be used to replace synthetic antioxidants in various food matrices.
The leftover lees have also been shown to be effective for the production of culture media for biotechnological applications, and yeast lees have also been also tested, with differing results, for application in animal feeding, food, and agriculture.
Additionally, wine lees could be exploited to obtain cell wall mannoproteins and β-glucans with several potential applications, especially in food production, winemaking, and viticulture.
These new studies could offer many possibilities to apply circular models in order to reuse wine lees.
Moreover, these models could provide the wine industry with a tool to improve not only its environmental impact but also its economic sustainability.