University of Udine Explores Mushroom-Derived Chitosan as a Greener Alternative for White Wine Stabilisation
- Gauri Khanna
- May 6
- 4 min read
Chitosan extracted from oyster mushroom stems could replace bentonite, a standard but wasteful clay-based fining agent, in white wine production.
The mushroom-derived treatment reduced problem proteins by up to 51% while leaving wine colour and polyphenol content essentially unchanged.
With global edible mushroom production generating up to 15 million tonnes of by-products annually, the feedstock potential is substantial.
White wine is, in many respects, a fragile product. Invisible proteins, derived from the grape itself, can form a haze inside the bottle after it leaves the winery. The effect is purely aesthetic, posing no safety risk, but it is enough to prompt consumer rejection and financial loss. For decades, winemakers have turned to bentonite, a natural clay, to strip these proteins out before bottling. It works, but it comes at a cost: wine volume is lost, aromas are stripped away, and the resulting waste creates disposal headaches. Researchers at the University of Udine, together with colleagues at the Fondazione Edmund Mach in Italy, have been investigating a more elegant solution, one grown from fungal by-products and extracted using nothing more aggressive than hot water.
What Is Chitosan and Where Does It Come From?
Chitosan is a biopolymer derived from chitin, the structural material found in crustacean shells, insect exoskeletons, and fungal cell walls. It is positively charged under acidic conditions, which makes it effective at binding and removing negatively charged proteins from solution. Commercially, most chitosan comes from crustacean shells, a source that is seasonal, geographically constrained, and can trigger allergies. Fungal sources offer a compelling alternative. Global edible mushroom production generates between nine and fifteen million tonnes of potentially usable by-product biomass each year, including the stems routinely trimmed and discarded before packaging. In contrast, crustacean fisheries yield roughly two and a half to three and a half million tonnes of shells annually, and these already supply around 70% of the world's commercial chitosan.
The Udine team extracted chitosan from the stems of oyster mushrooms (Pleurotus ostreatus) using subcritical water processing, a technique in which water is held at elevated temperature and pressure, just below its boiling point at standard pressure, to dissolve and separate target compounds without harsh chemicals. The method yielded a chitosan with a degree of deacetylation of 82%, a low crystallinity index, and a strongly positive surface charge, all characteristics associated with high reactivity and effective protein binding. As work on mushroom-derived chitosan for packaging applications has also demonstrated, fungal sources can match or exceed the functional performance of conventional crustacean-derived material.
Testing the Fining Agent Across Three Wine Varieties
The researchers applied the mushroom-derived chitosan to three white wines exhibiting protein instability: Graševina and Malvasia from the Istria region of Croatia, and Traminer from Trentino-Alto Adige in Italy. Dosages of 20, 60, and 100 grams per hectolitre were tested. The maximum permitted by the International Organisation of Vine and Wine for fining purposes is 100 g/hL.
Results varied by grape variety. Graševina, which had comparatively moderate initial protein instability, showed a 44% reduction in heat test instability at the highest dosage. Malvasia and Traminer, both starting with higher protein loads, responded less dramatically, with average instability reductions of around 21% in Malvasia at the same dose. In terms of pathogenesis-related proteins, the specific fractions most implicated in haze formation, reductions of up to 51% were recorded in Malvasia at 100 g/hL. Complete stabilisation was not achieved in any variety, suggesting that mushroom-derived chitosan may work best as part of a broader stabilisation protocol rather than as a standalone replacement for bentonite.
Critically, the treatment had no significant effect on total polyphenol content or wine colour in any of the three varieties tested. This matters because polyphenols contribute to astringency, mouthfeel, and colour stability, qualities that bentonite is known to diminish. At the highest dosage, the chitosan treatment also increased the wines' resistance to oxidative browning, reflecting the antioxidant properties the polymer carries with it.
Preserving Aroma While Reducing Waste
The impact on wine aroma was more nuanced. Ester concentrations, compounds responsible for fruity and floral notes formed during fermentation, fell by up to 26% at the maximum dosage. However, the key aroma compounds remained above their sensory detection thresholds in all cases, meaning the overall aromatic profile was not meaningfully compromised in practical terms. Alcohols, fatty acids, terpenes, and norisoprenoids, the latter being the compounds responsible for much of Traminer's distinctive floral character, were largely unaffected.
The broader significance of this research extends well beyond the winery. The circular economy logic here is straightforward. Mushroom cultivation generates vast quantities of stem waste; that waste contains chitin; that chitin can be converted into a functional fining agent. As fungal fermentation increasingly transforms agricultural side streams into high-value ingredients, the winemaking sector now has reason to pay closer attention to what the mushroom industry discards. The researchers acknowledge that sensory trials are still needed to complement the chemical data, and that further work on dosage optimisation across a wider range of grape varieties remains necessary. But the underlying case, for replacing a waste-generating clay with a waste-derived biopolymer, is already a credible one.
