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Specific Flavor Compounds Derived from Nelson Sauvin Hop and Synergy of these Compounds - Based on a poster presented at the 32nd Congress of the European Brewery Convention, Hamburg, Germany, May 2009
Takoi, K., Degueil, M., Shinkaruk, S., Thibon, C., Kurihara, T., Toyoshima, K., Ito, K., Bennetau, B., Dubourdieu, D., Tominaga, T.

Nelson Sauvin (NS) is a unique hop cultivar that gives a specific flavor (exotic fruit-like, Sauvignon Blanc wine-like) to finished beers. We have attempted to identify the specific flavor compounds derived from NS. First, isobutyric esters, including 2-methylbutyl isobutyrate (2MIB), have been found in the beers used with NS (NS product). These compounds had a green apple-like and/or apricot-like flavor. We next focused on certain volatile thiols that are well known to contribute to wine flavors, especially Sauvignon Blanc, and identified two new volatile thiols, 3-sulfanyl-4-methylpentan-1-ol (3S4MP) and 3-sulfanyl-4-methylpentyl acetate (3S4MPA), having a grapefruit-like and/or rhubarb odor, similar to that of Sauvignon Blanc. Among these compounds, 3S4MP was contained twice of its thresholds and 3S4MPA and 2MIB were contained below their threshold, in the NS product. However, it was confirmed that 3S4MP enhanced the flavors of 3S4MPA and 2MIB by synergy. In addition, we also confirmed that 3S4MP enhanced the flavors of terpene alcohols (linalool and geraniol). Therefore, we concluded that 3S4MP might contribute to the specific flavor of the NS product as a key compound having two roles, its own characteristic flavor and its function as a flavor enhancer.In general, various hop cultivars have different aroma characters, and beers brewed with certain hops have cultivar-specific flavors. The flavor compounds of hops are mainly derived from the hop oil included in the lupulin gland of hop cone. Several terpenoids (myrcene, humulene, linalool, etc.), esters, aldehydes and ketones were well known as the major flavor compounds in the hop oil. However, the key compounds that contributed to the cultivar-specific flavors of the various hops, especially the flavor of beer using a certain hop, have not been completely clarified. Therefore, new techniques for the evaluation of the hop flavor characteristics are needed.Recently, several researchers have focused on volatile thiols having very low threshold as characteristic flavor compounds in beer. Among various volatile thiols, beer researchers have mainly focused on 3-methyl-2-butene-1-thiol (3MBT), as a light-struck skunky off flavor [1]. On the other hand, wine researchers have revealed the contribution of volatile thiols to cultivar-specific 'fruity' flavors of certain white wines [2, 3, 4, 5]. For example, 4-methyl-4-sulfanylpentan-2-one (4MSP) and 3-sulfanylhexan-1-ol (3SH) were contributed to the cultivar-specific flavor of Sauvignon Blanc wines [2, 3, 4]. 4MSP had a box tree-like flavor and its threshold was about 0.8 ng/L. 3SH had a grapefruit-like flavor and its threshold was about 60 ng/L. In addition, 3-sulfanylpentan-1-ol (3SP) and 3-sulfanylheptan-1-ol, having grapefruit-like flavor similar to the one of 3SH, were also identified in botrytized sweet wines [5]. These compounds were present in very small amounts in the wines, but they contributed to the specific flavor of the wines [2, 3, 4, 5]. C. Vermeulen et al. reported the occurrence of a very small amount of volatile thiols, including 3MBT, 4MSP and 3SH, in various commercial beers [6]. However, most of these thiols have negative flavors for beer, like onion, burnt, meaty, roasted, etc., except for 3SH and 4MSP, and the amounts of 3SH and 4MSP in the beers that they analyzed were both at trace levels [6]. M. Steinhaus et al. proposed that 4MSP was one of the key compounds contributed to the cultivar-specific flavor of Cascade hop [7, 8]. T. Kishimoto et al. compared the concentrations of 4MSP among various hop cultivars and found that hop cultivars grown in US, including Cascade, contained larger amount of 4MSP than those grown in Europe [9]. They also analyzed 3SH and 3-sulfanylhexyl acetate (3SHA) during beer brewing process and suggested that these thiols increased during beer fermentation as well as wine fermentation [10].

Descriptors: beer aroma, hop, Nelson Sauvin, flavor, isobutyric esters, thiols, synergy

BrewingScience - Monatsschrift fr Brauwissenschaft, 62 (July/August 2009), pp. 108-118