SPOILAGE OF VANILLA
Vanilla beans are quite susceptible to infection by penicillium and asperfillus molds and this generally occurs during the conditioning and subsequent storage periods (Bouriquet, 1954). In appearance, there are two types of mold: one is white at first and turns green later, while the other is black and spreads rapidly. Infection always begins at the stem end of the bean and, if left uncontrolled, the whole bean becomes wrinkled, dry and acquires a disagreeable odor. It is virtually impossible to eliminate the odor once the mold takes hold and this considerably detracts from the market value. Mold infection most frequently occurs with beans which have been harvested before they are mature. Development of mold is also encouraged if the beans are not killed properly, as they then do not dry uniformly, and if the beans have an excessive moisture content on conditioning. Sweating and drying the beans in the sun also leads to a higher incidence of mold than when an oven is used. Other contributors are dirty blankets and a general lack of cleanliness and ventilation in the curing room.
Vanilla beans are prone to attack by mites of the Tyrophagus species (Chalot and Bernard, 1920: Mallory and Cochran, 1941: Bouriquet, 1954) which imparts a disagreeable odor to the beans. The mites appear during conditioning, shipment of subsequent storage and may be detected by the small holes which they produce in the beans. In cases of limited infestation prior to shipment, alcohol treatment or sunning is often effective.
Some beans develop a creosote-like aroma which is impossible to eliminate once formed. This off-aroma generally becomes apparent at quite an early stage in the sweating process and results from an abnormal fermentation due to poor handling and curing practices. The principal cause is believed to be improper storage methods for fresh beans prior to killing. This undesirable fermentation can be avoided if fresh beans are stored in well-ventilated small piles, and by commencing curing as soon as possible.