In the pursuit of sustainable and environmentally sensitive winemaking, the handling of byproducts can’t be neglected. Wineries produce enormous amounts of both solid waste and liquid waste which can’t be simply dumped into the environment without serious consequences. Safe and appropriate disposal, however, costs money and often means discarding potentially valuable resources which, when properly applied, could save farmers and winemakers significant money in operational expenses. One persistent challenge, however, is the sheer volume of waste produced, particularly in popular wine-producing regions. Often, the volume of waste completely overwhelms a local economy’s ability to absorb and reuse it.
Nevertheless, successful reuse and repurposing of winery by-products, including grape stems, skins, seeds, and yeast-laden lees produced during fermentation, can achieve several goals: divert waste from landfills, re-use nutrients in a beneficial way, and potentially create valuable products that can be sold to benefit the bottom line.
Wastewater
Wastewater, or process water, that is produced during the winemaking process is a particularly challenging byproduct for winemakers to manage. Winery wastewater is characterized by extremely high levels of organic pollutants — mostly soluble sugars, alcohols, acids, tannins, lignin, and compounds such as polyphenols, which persist in nature and resist degradation. Creative and careful treatment strategies are key to preserving clean water, an increasingly scarce and valuable resource.
Water Scarcity
Clean, fresh water is becoming increasingly scarce as our population, industrial activities, and agriculture continue to expand. The demand on previously “infinite” water supplies, such as the Colorado River and enormous networks of underground aquifers, has drained many of those to historic lows and sometimes rendered the remaining water too contaminated for use as drinking water or even agriculture. In some cases, water has become so scarce that wineries and other key agricultural operations have had to cut down production when farms and vineyards were cut off altogether from supplemental water supplies. In California, nearly 1000 landowners in the heart of wine country were told they wouldn’t get enough water to sustain their vineyards through the 2021 season. In our changing climate, not only are temperatures rising, but weather events, from droughts to extreme storms, are becoming the new pattern. Since agriculture doesn’t respond well to a continuing series of droughts and floods, owners and managers are faced with finding ways to capture, treat, and store this increasingly precious resource, all in the name of sustainability.
Reusing Wastewater
Agricultural wastewater can be used for other purposes as well, many of which don’t require high levels of treatment. Regardless of the ultimate use, the beneficial use of winery wastewater not only reduces waste and conserves resources, but also provides opportunities for renewable energy production and other innovative solutions.
- Irrigation is a common use for winery wastewater, both for wine grapes and other crops. Winery wastewater, composed of a high amount of organic compounds, including sugars, can be treated with microorganisms that break down the compounds and convert them to nutrients and minerals that support plant growth and fruit production. While wastewater used for irrigation may be diluted to reduce high concentrations of salts or other contaminants from overwhelming soil biota, the overall consumption of fresh water can be greatly reduced.
- When it’s been screened and treated with beneficial bacteria, winery wastewater carries high levels of nitrogen and phosphorus. These nutrients create challenges for surface water sources, but they make excellent fertilizer for crops. Farmers who use partially treated winery wastewater can save money not only on water purchases but on chemical fertilizers.
- Winery wastewater that’s treated using anaerobic digestion releases methane that can be collected and used as a renewable energy source. Farmers may sell the collected methane or use it to supply heat or electricity in their own operations. Either option contributes to the winery’s bottom line.
- Aquaculture is an increasingly popular method for raising fish, shellfish, and algae for food production. In ponds or tanks, these operations require a steady supply of nutrients for both the fish and the plants, which can be supplied by treated winery wastewater.
- Some treated winery wastewater can even be reused in the wineries themselves, employed for cleaning and sterilizing wine making equipment.
Solid Waste
A popular use of solid waste from the winemaking process is the production of compost. The solid waste is typically grape skins, pulp, seeds, and may include ground up stems. Coupled with judicious use of winery wastewater, this produces a high-quality compost that suppresses weeds, retains moisture, contributes vital nutrients, conditions the soil, and improves soil quality.
Pomace
Pomace refers to the solid remains of various types of fruits after they’ve been pressed for juice or oi. Grape pomace is composed of stems, skins, pulp, seeds, and lees that are filtered out during fermentation.
Pomace can represent 20-25% of the original weight of grapes used for wine. In California alone, about 100,000 tons of pomace are produced each year. The sheer volume of this byproduct makes recycling a critical goal for sustainability, not only in the effort to reduce the pressure on landfills, but to recover valuable resources that make up the waste.
In some cases, grape seeds may be extracted from pomace before it is composted. The seeds may be pressed for grapeseed oil or ground up and used as valuable nutritional supplements. The greater portion of pomace, even when produced from fermented grapes, is composed of a staggering variety of chemical compounds. Traditionally, pomace can be processed to create cream of tartar, a common product often found in the spice aisle of your grocery store. It can be distilled into grappa, a traditional Italian spirit, used as food coloring (reds, purples, and blues), or turned into animal feed.
Some more innovative uses for pomace include the production of bioplastics, such as net clips, which are used in vineyards to protect ripening grape clusters from birds and other pests.
Grape pomace is increasingly recognized as a high value bioactive source with a variety of benefits for human health. The main component of grape pomace is dietary fiber, which contains a high number of antioxidants. Phenolics derived from pomace have been shown to improve blood pressure, prevent cardiovascular disease, and improve fasting glucose in humans. An impressive array of other potential health benefits are currently being investigated and may convert this byproduct from an inconvenience to a valuable commodity.
Based on the polyphenolic content of grape pomace, scientists have suggested that winery-derived pomace could be a source for natural antioxidants. These antioxidants could be valuable in a variety of pharmaceutical, cosmetic, and food industries. The cosmetic industry has shown particular interest in the use of antioxidants like anthocyanins and tannins to disguise or delay signs of aging.
As wineries continue to work on new uses for this prodigious byproduct, pomace is being baked into protein bars, used in spa treatments, and studied for potential use as a natural alternative to artificial preservatives in food.
Lees
Wine lees are composed primarily of yeast cells that settle at the bottom of tanks during fermentation and form a sludge-like material. Lees are typically collected as wine is racked and have been identified as a natural source of phenolic (antioxidant) compounds. Yeast lees could be used to produce spreads, calorie-free thickeners, flavor enhancers, and food additives. On a local level, lees may also be combined with pomace and composted to create a soil conditioning agent.
