Kanako Yanagisawa, Harumi Kikuchi, Fumiko Tanzawa, and Kanako Sasaki*
*Kirin Holdings Company, Limited, 26-1-12-12 Muraoka-Higashi 2-Chome, Fujisawa, Kanagawa, Shonan Health Innovation Park, 251-8555, Japan (Kanako_Sasaki@kirin.co.jp)

The objective of this study is to reveal the cause of an India ink-like off-flavor in Syrah berries and wine made from grapes grown in a vineyard in Japan in 2020 and 2021. Microbial contamination was suspected as the cause because this off-flavor was detected not only in wine, but also in Syrah berries. Thus, the study was conducted to identify the fungus and the specific flavor compound(s) responsible.

Grape berries collected during harvest, with a similar India ink-like odor, were used for this study. Fungi were isolated from these berries by rinsing the surface and culturing the rinse water on an agar medium. About 20 fungal strains were isolated and one released a strong India ink-like odor. This strain was identified as a Coniella spp., known as grape white rot fungus. Furthermore, we found that the Syrah berries infected with this strain released the India ink-like odor, while control berries did not. The aroma compounds of infected/non-infected berries were analyzed using the SIM/Scan mode of gas chromatography-mass spectrometry. These berries were incubated in a closed container and the odorous compounds were collected in a TENAX GC collection tube (P/N: 223-57102-91) by nitrogen purge. Several compounds were identified, such as fenchol, 2-methylisoborneol (MIB), and benzofuran, that are specific to the infected berries. It was considered that MIB is the candidate compound for the cause of this off-flavor because of its camphor-like odor.

The study concluded that the India ink-like off-flavor is caused by generation of MIB during infection by Coniella spp. This is the first report that Coniella spp. can produce MIB. These new insights are expected to contribute to production of high-quality grapes and wines.

Funding Support: Kirin Holdings Company, Limited