Elias Bushen* and Aude Vernhet
*DelRio Vineyards, 635 S 5th St., Jacksonville, OR 97530 (elias@delriovineyards.com)

Fining with a yeast protein extract (PYXT) was shown to result in a decrease of the haze formation induced in white wines. Heat tests are used widely in enology to control white wine stability/instability through their impact on unfolding and precipitation of wine proteins. The experiment studied the impact of yeast extracts, then fractionated them and identified the nature and properties of the active fraction/s. A decrease in heat-induced haze was observed by yeast extract fining with the soluble fraction. These experiments were linked to SDS-PAGE analyses for wine proteins. Slight changes in protein profiles were observed after fining with PYXT. The fining did not seem to affect thaumatine-like proteins (18 to 25 kDa). Protein bands usually attributed to invertase, chitinases, and β-glucanase (between 30 and 60 kDa) were no more detected after fining. Dynamic like scattering experiments in real and model white wine were also performed. These different experiments indicated that the impact of PYXT is neither related to removal of wine proteins during fining nor to prevention of heat-induced aggregation of the later. More likely, this impact is linked to a decrease of the final aggregate size distribution and/or a change in their shape and structure. Such mechanisms have been proposed to explain the effect of different specific mannoproteins, called haze protective factors. A soluble fraction with molecular weight >10 kDa lowered heat-induced aggregation, and the results of fractionation procedures provided indications for further trials.

Funding Support: Scholarship and Thesis internship sponsored by Lallemand