Kate Macreadie conducted the trials at the Nelson Marlborough Institute of Technology (NMIT) last year, in her final year of the Bachelor of Viticulture and Winemaking.
Kate tested eight calcium bentonites to ascertain their effects on calcium concentrations in treated Sauvignon Blanc wine. “To determine these effects, a model Sauvignon Blanc wine was treated with each bentonite type at increasing industry-standard rates of up to 4g/L and then spectrophotometrically analysed to determine calcium concentrations,” her report says. There was a positive correlation between dose rate and calcium concentrations in all the bentonites trialled, “with strength of correlation varying from modest to very strong”.
Kate says the work adds to the findings of a 2016 study investigating a range of commercial bentonites on New Zealand Sauvignon Blanc wine, providing “greater data reliability due to increased treatment replicates and a calcium-specific research focus”.
The research – which specifies results for eight different products – will provide winemakers with evidence that calcium concentrations in Sauvignon Blanc wine will increase relative to increasing bentonite application rates, says Kate. She notes that the research focussed on statistically significant changes in calcium concentrations, “but it is important to consider the results relative to real world winemaking”.
Stewart Field, who is a viticulture lecturer and researcher at NMIT, says Kate has completed an “outstanding” piece of research for her student project. “She observed calcium tartrate precipitation in the winery that drove a keen personal interest to investigate further.” He says the results will not only benefit the winery where she works, “but hopefully has informed the Marlborough wine industry that bentonite application to wine needs careful consideration”.