Aging in oak barrels is widely used in enology which could bring flavor changes and aromatic complexity to wines. In the present study, the aroma compounds were analyzed from the ‘Merlot’ dry red wines, which were fermented in two types of fermenters (stainless steel tank and rotated oak barrel) and aged in six types of oak barrels (three geographic origins × two toasting degrees) for different time (0, 3, 6 and 9 months, respectively). Results showed that 30 volatiles were associated with barrels and increased during oak aging. The fermenters could influence the intensities of the toast, leathery, smoky, fruity, floral and caramel aromas. The concentration of whisky lactone, eugenol, cis-isoeugenol, and the intensities of the toast and spicy aromas were highest in the wines aged in American oak and were lowest in the wines aged in French oak barrels. The concentrations of guaiacol, syringol, trans-isoeugenol, furfural alcohol, vanilla, cis-whisky lactone enabled the medium toasting barrels to be distinguished from the light toasting ones. The compounds originating from the barrels could be used to distinguish the types of different barrels, but the other general grape-derived and fermentation-derived volatiles could not. The fermenters, oak species and toasting degrees of the barrels all had significant effects on the aroma profiles of the aged ‘Merlot’ dry red wines, but the influence of the geographic origin was not obvious.

Protein haze was one of the main causes of the instability of white wines. Proteins that caused haze or precipitation in white wines mainly came from grape fruits, and their compositions and contents were affected by many factors such as fruit diseases, harvesting methods and water stress. Unstable wine proteins were usually pathogenesis-related (PR) proteins of grapes, mainly chitinases and thaumatin-like proteins (TLPs), which had lower isoelectric point (pI) and smaller molecular weight, and were highly resistant to the low pH values of wines and the protease hydrolysis during fermentation. At present, the technology of protein stabilization and clarification in white wines mainly included bentonite fining, heat treatment, enzymatic hydrolysis, polysaccharide treatment and ultrafiltration methods. Among them, the most commonly used method was bentonite treatment. In this paper, the research progresses of the origin, mechanism and influencing factors of the unstable proteins in white wines were summarized, and the applications, advantages and disadvantages of various clarification techniques were also concluded, in order to provide some support for the theoretical and technological research of the protein stability in white wines in the future.