Yeast Strain Selection to Produce Sulfur Dioxide-Free Merlot Wine (2017)

This study examines the efficacy of non-Saccharomyces yeast selection to produce wines without the use of sulfur dioxide. Merlot grapes were harvested on September 28 and stored overnight at 45°F. The next day fruit was destemmed, sorted, and crushed into two separate bins (0.5 tons per treatment). One bin received 6g/hL sulfur dioxide (control), and the other received 5g/hL Primaflora VR Bio (AEB) as a sulfur dioxide replacement (no sulfur dioxide treatment). Both bins received a two day cold soak (one punchdown per day, with dry ice additions), and then the control bin received 15g/hL FX10, and the treatment received 15g/hL FX10. At this point the bins were moved out of the cold room in order to warm up. Punchdowns were twice per day until fermentation became vigorous (October 6), which then received 3 punchdowns per day. Fermentation lasted for 8 days, after which the wine was drained off the skins and put into stainless steel tanks for aging (only free run was used). On November 30, wines were filtered with K250/EK filters and sterile filtered (0.45 micron) and bottled on December 7. At bottling, the control received 1g/hL sulfur dioxide. The wine without sulfur dioxide had slightly less alcohol and lactic acid, and slightly increased volatile acidity. It also had less color and had a slightly longer lag phase in fermentation. The no sulfur dioxide wine seemed to have more yeasts throughout its life except for Hanseniaspora, relative to the control. Both fermentations had similar bacterial counts. Overall, judges were more or less able to correctly distinguish the wines made with and without sulfur dioxide, although in one tasting this was statistically significant and at the other it was not. Judges tended to prefer the wine made without sulfur dioxide. The no sulfur wine may have had higher Fruit Intensity, higher Overall Aromatic Intensity, and higher perceived Acidity relative to the wine made with sulfur dioxide.

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