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The final product of this process is the cured, dry bean that has not only become shelf-stable but has also developed the familiar vanilla flavor, the latter having been formed as a result of very many chemical and enzymatic reactions that occur concurrently during the curing process. Every vanilla-growing country has developed its own specific curing process, but all of these generally consist of four main steps, namely killing/blanching, sweating, drying and conditioning. Killing is very often achieved by submerging the freshly picked green beans in hot water for a short time (e.g. 55–60°C for about 3 min) during which the vegetative phase is stopped.
In the sweating step, the hot beans are kept wrapped in blankets, thus maintaining a temperature of about 45–50°C for one or two days. During this period endogenous enzymes are active and the beans develop their characteristic brown color.
During the remaining months of the process, the beans undergo passive drying until they have a dry substance level of about 70–75%, thereby becoming microbiologically shelf-stable. Many (bio)chemical reactions take place in the course of this long production process, some of which result in the formation of low molecular weight, flavor-active compounds that together contribute toward the final flavor of the cured bean.
The main biochemical reaction occurring during the curing process is the hydrolysis of the glucovanillin (the beta-glucoside of vanillin), which is catalyzed by the beta-glucosidase endogenously present in the green bean. A certain amount of hydrolysis can also occur before the green bean is picked from the vine, whereby the degree of hydrolysis depends upon how ripe the bean actually is before being picked.
The fate of glucovanillin and vanillin have been studied during the various steps of the traditional curing process as performed on the island of Réunion. In this present publication, the findings made during the traditional curing process performed during the 2005 season in Madagascar are described, and, in particular, an attempt is made to explain how some of the vanillin losses occur during the process.
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