WINETECH Technical Yearbook 2020

in its lees. It is estimated that 3-20% of wine volume is lost with bentonite lees. Bentonite is also not recyclable and there are labour and waste disposal issues. As a result, research for an alternative to bentonite has been ongoing for the past 30 years. WHAT CAUSES PROTEIN INSTABILITY? Grape juice and resulting wines contain many different proteins in various concentrations (anywhere from 10-400 mg/L in total). Not all of them become unstable and form a haze under the conditions that wines are exposed to during their lifetimes. In fact, it is only the so-called pathogenesis-related (PR) proteins, with their low denaturation temperatures that are the culprits. These proteins are fairly small and compact with a globular structure. The two main types are chitinases and thaumatin-like proteins (TLPs). Chitinases are more sensitive than TLPs to elevated temperatures (above 40°C). Once its globular structure has unfolded (denatured), it is not possible to refold if conditions become favourable again, i.e. the ship moves further away from the equator. Some TLPs, on the other hand, can refold. Unfolded proteins can attract each other to form an aggregate, which eventually becomes big enough to be visible to the naked eye and thus the dreaded haze is formed.

Winetech vine and wine innovation watch: Magnetic nanoparticles for the protein stabilisation of wines

WHO DID WHAT? Australian researchers found that acrylic- acid-based plasma polymer coated magnetic nanoparticles can effectively protein stabilise white wines. WHY WAS THIS INVESTIGATED? Currently mostly white wines are treated with bentonite before bottling. This is to prevent a protein haze from forming as a result of elevated temperatures during storing and transport. Bentonite, although fairly inexpensive, can potentially alter a wine’s chemical and sensory characteristics. In addition it is a clay, which when it settles, contains some wine

AUGUST 2020

KARIEN O’KENNEDY: Winetech, Paarl KEYWORDS: Protein stabilisation, magnetic separation technology

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