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Lees, a valuable waste product

Every year when the alcoholic fermentation is over, the fermentation tanks are cleaned and the residual lees are removed. This mixture of dead yeast cells, tartaric acid crystals and residual organic material from the grapes can amount to many thousands of liters per vineyard. Are the lees a waste product or a valuable by-product of the vinification?

Harmful waste product

Wine lees are a rich source of nutrients and complex organic compounds, but are often washed away with waste water. The lees are rich in nitrogen and phosphorus compounds and therefore have the potential to serve as fertilizer in the vineyard. However, high concentrations of potassium and sodium ions in the lees have a negative effect on the soil. They displace other essential positively charged ions and as such disturb the structure and balance of the soil1,2. This causes shortages in the soil with all kinds of adverse effects on the growth of the grapevine. Not only the soil structure, but also the entire ecosystem in the vineyard can be disturbed. The low pH (of around 3.4) of the lees and high concentrations of salts and organic compounds have a toxic effect on small organisms such as duckweed and water fleas. Environmental impact is often measured on the basis of these two organisms. Both are an important food source and a demonstrably toxic effect on these organisms can therefore have consequences for the entire food chain3. Processing the lees by adjusting to a neutral pH or by diluting may however reduce the toxicity.

Lees, from wine tank to powder
Lees, from wine tank to powder. Left: the lees at the bottom of a tank after the wine is pumped away. Middle: the solid substance of the lees. Right: the lees when it is dried and ground into powder.

Antioxidants

Polyphenols – chemical compounds from plants such as tannins, anthocyanins and stilbenoids – are also highly present in the lees. Polyphenols often have a biological or antioxidant effect that can be used in the food and pharmaceutical industries4, 5. In particular, the lees of red wine contain many polyphenols with a high anti-oxidative effect6, of which resveratrol is the best known. It is often difficult to obtain specific antioxidants and other organic compounds. However, wine lees are a cheap resource of these valuable molecules and are easy to process. That is, as a result of the fermentation, the seeds and skins of the grapes in which the polyphenols are contained have already completely disintegrated. It is therefore no longer necessary to grind and break down solid organic matter6, 7.

Molecule structures of phenolic compounds that are present in wine lees
Phenolic compounds that are present in wine lees.
Adapted from Jara-Palacios, 2019 via CC BY-4.0

Mice and ice cream

All those antioxidants in the lees, that offers possibilities for applications in the medical world or the food industry. Eating a juicy steak, or fries with mayonnaise causes an increased cholesterol level, and all kinds of oxidative reactions that can cause damage to your cells and tissues. (Enjoy in moderation). Eating wine lees can prevent this oxidation and reduce the increase in cholesterol levels, as demonstrated in a study on mice. Mice on a high-fat diet that also had lees added to their food had a lowered ‘total’ cholesterol, less of the ‘bad’ LDL cholesterol and the anti-oxidative values ​​in their liver were increased compared to mice fed only the high-fat diet8. Thus, eating French fries every day should be fine, as long as you dip them in lees…

Icecream cone

Dairy products, and also ice cream, contain much of the unhealthy LDL cholesterol9. Unhealthy stuff, but what if you add lees in the mix they must have thought in Taiwan? Researchers from Chung-Hwa University of Medical Technology in Taiwan have made ice cream containing the (unprocessed) lees of red wine. They show that the anti-oxidative effect of the polyphenols is retained during the making of the ice, so that a healthier ice cream is actually created. The addition of lees decreased the specific gravity, firmness, lightness and melting rate of the ice10. Ice cream packed with antioxidants that does not immediately drip onto your shoes, who doesn’t want that?!

READ NOW: Sonication of yeast cells accelerates aging on lees

Although the use of unprocessed lees as described above is practical, it is probably not desirable to actually include all components of the lees (including the high concentrations of salts) into the food. The pharmaceutical industry is even stricter and will only want to include a number of specific molecules into their products. Fortunately, it is possible to filter the active polyphenols from the lees5. This can be done by drying, grinding the solid and then separating it by using chemical methods4, 5.

Waste or by-product?

Lees is a valuable by-product of the vinification and contains polyphenols that are difficult to obtain. The food and pharmaceutical industry can use the winery waste to acquire antioxidants, and there are companies that specialize in processing it into value-added products. Not only can winemakers earn money by selling the lees, it also prevents the release of large amounts of this low-pH (toxic) solution in the sewerage or the environment. Unfortunately, the companies that process winery waste can be scarce, which makes it difficult to find a market for the lees. To further approach a circular economy, it would be nice if more wineries would find a way to reuse their waste products. In the worst case, the lees can always be used to make ice cream…

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References:
1.   Moldes AB, Vazquez M, Dominguez JM, Diaz-Fierros F, Barral MT. Negative effect of discharging vinification lees on soils. Bioresource technology. 2008;99(13):5991-6.
2.   Hirzel, D. R., Steenwerth, K., Parikh, S. J., and Oberholster, A. (2017). Impact of winery wastewater irrigation on soil, grape and wine composition. Agricultural Water Management: 178-189.
3.   Australian Government. IMPACT OF WINERY WASTEWATER ON ECOSYSTEM HEALTH.
2006 https://www.wineaustralia.com/getmedia/04155f38-1a25-4c5a-a539-4919423a19d7/Impacts-report-CSIRO.pdf Geraadpleegd op 19-03-2019.
4.   Barcia MT, Pertuzatti PB, Rodrigues D, Bochi VC, Hermosin-Gutierrez I, Godoy HT.
Effect of drying methods on the phenolic content and antioxidant capacity of Brazilian winemaking byproducts and their stability over storage. International journal of food sciences and nutrition. 2015;66(8):895-903.
5.   Jara-Palacios MJ. Wine Lees as a Source of Antioxidant Compounds. Antioxidants (Basel, Switzerland). 2019;8(2).
6.   Zhijing Y, Shavandi A, Harrison R, Bekhit AEA. Characterization of Phenolic Compounds in Wine Lees. Antioxidants (Basel, Switzerland). 2018;7(4).
7.   Yammine S, Brianceau S, Manteau S, Turk M, Ghidossi R, Vorobiev E, et al. Extraction and purification of high added value compounds from by-products of the winemaking chain using alternative/nonconventional processes/technologies. Critical reviews in food science and nutrition. 2018;58(8):1375-90.
8.   Landeka I, Jurcevic, Dora M, Guberovic I, Petras M, Rimac S, et al. Polyphenols from Wine Lees as a Novel Functional Bioactive Compound in the Protection Against Oxidative Stress and Hyperlipidaemia. Food technology and biotechnology. 2017;55(1):109-16.
9.   https://mens-en-gezondheid.infonu.nl/dieet/111480-cholesterol-welk-voedsel-bevat-veel-ongezonde-cholesterol.html Geraadpleegd op 19-03-2019
10.   
Hwang J-Y, Shyu Y-S, Hsu C-K, Grape wine lees improves the rheological and adds antioxidant properties to ice cream. LWT – Food Science and Technology. 2008;42:312-318. www.doi.org/10.1016/j.lwt.2008.03.008

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