Wen-Yin Chueh, Qun Sun,* Shunping Ding, and Misha Kwasniewski
*California State University, Fresno, 3547 Trenton Ln., Clovis, CA, 93619 
(qsun@csufresno.edu)

Chardonnay is the most widely planted variety in the Central Coast of California, but it is susceptible to many diseases, notably powdery mildew and botrytis bunch rot. Synthesized fungicides are commonly used in vineyards. However, these fungicides are costly and can harm the environment and human health. Moreover, frequent use of fungicides selects for pathogen resistance. The objective of this project was to investigate the impact of biofungicides on Chardonnay wine fermentation and wine aromatic profile. Eight experimental trials on Chardonnay winegrapes were conducted, including three combinations of biofungicides and synthetic fungicides, two with synthetic fungicide, two with biofungicides, and one untreated control. The grapes were crushed and pressed immediately after harvest in 2021. Both free-run and press fraction juice was racked into one gallon of glass carboys. The yeast EC-1118 was inoculated into the juice for alcoholic fermentation. During fermentation, the yeast population was enumerated every day, and Winescan was used to monitor fermentation status, including glucose, fructose, pH, TA, ethanol, and volatile acidity. Fermentation was considered complete when the residual sugar was <2 g/L. Upon completion of fermentation, potassium metabisulfite was added to maintain 40 mg/L free sulfur dioxide. The wines were stabilized at 2°C and screened for faults by an expert sensory panel prior to bottling. The finished wine was also measured for aroma compounds by headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). Chardonnay berries sprayed with the biofungicide showed normal fermentation. All wines made from biofungicide-treated berries had a similar chemical composition profile to the control wine. The range in alcohol content was 12 to 13%. Residual sugar and volatile acidity were <2 g/L and 0.5 g/L, respectively. The pH was maintained at 3.2 to 3.3, and titratable acidity at 7.6 to 8.2 g/L. There was no significant difference in aroma compounds such as linalool, beta-damascenone, 3-hexen-1-ol, isoamyl hexanoate, 1-octanol, 1-nonanol, or methyl salicylate among treatments. This study indicated that biofungicides may be used as an alternative to synthetic fungicides for Chardonnay wine.

Funding Support: Agricultural Research Institute