Stages of production
The pods are harvested while green and immature. At this stage, they are odourless.
Both the vanilla orchid and the ripe vanilla bean lack aroma. It is only during the curing process that glucovanillin, a vanillin precursor formed during the ripening of the vanilla fruit, is enzymatically converted to glucose and vanillin. The longer a bean vine-ripens, the more concentrated the vanillin and other flavor compounds are after curing. Higher vanillin indicates higher bean quality, which impacts the beans' market value. Beans left on the vine split and decrease in quality. Curing should begin within a week after harvest.
The Mexicans developed the original, labor-intensive, five- to six-month process for curing green vanilla beans. The "Bourbon" process, named for the original designation of the island of Reunion, is a result of slight modifications made by the French. This method, which takes about four to six months, is currently practiced in Madagascar, Comoros, and Reunion. Indonesian beans were originally picked while they were still immature to avoid theft. Although their curing process takes from several weeks to two months, the Indonesians have begun to adopt Bourbon growing and curing practices to increase their bean quality.
The curing process varies among growing regions and many bean curers use a combination of techniques, yet all curing methods involve four phases that directly affect the amount of vanillin and other flavor components in the beans:
The vegetative tissue of the vanilla pod is killed to prevent further growing. The method of killing varies, but may be accomplished by sun killing, oven killing, hot water killing, killing by scratching, or killing by freezing. Heat is applied to the pods by letting them sun-dry, as in the traditional Mexican method, or by submersing them in hot water for several minutes, as in the Bourbon process.
The pods are held for 7 to 10 days under hot (45º-65ºC) and humid conditions; pods are often placed into fabric covered boxes immediately after boiling. Sweating the wilted beans involves rapid dehydration and slow fermentation allowing enzymes to process the compounds in the pods into vanillin and other compounds important to the final vanilla flavor.
To prevent rotting and to lock the aroma in the pods, the pods are dried. Often, pods are laid out in the sun during the mornings and returned to their boxes in the afternoons. When 25-30% of the pods' weight is moisture (as opposed to the 60-70% they began drying with) they have completed the curing process and will exhibit their fullest aromatic qualities.
Once fully cured, the vanilla is sorted by quality and graded.