Handbook of Vanilla Science and Technology

The two commonly used killing methods in Mexico are sun-killing and oven-killing (Childers and Cibes 1948; Theodose 1973). In the sun-killing method, green-mature beans are first sorted according to size and stage of maturity and defined as primes or seconds, or split-beans, based on size and appearance (Figure 6.13). Beans are then placed on dark woolen blankets and exposed to the sun for about 4 to 5 hours. When beans become warm to the touch, they are covered by the blanket edges and left in the sun until mid- to late afternoon. The blankets are rolled, taken indoors to sweat in mahogany boxes, which are lined and covered with mats and blankets. This process is repeated up to 6 to 8 times until all the beans have turned uniformly brown, evidence that the killing process has been completed. During this process, the beans lose moisture rapidly and become supple. This phase is followed by additional shorter “sunnings” and infrequent sweating for an additional 2 weeks. The beans are then placed indoors on racks and subjected to slow drying at ambient temperatures, lasting around 1 month, and are inspected regularly. Beans that have dried sufficiently are separated for the subsequent stage of conditioning. The entire process requires about 8 weeks.

Fig. 6.13 Mexican Curing method. Mature-green vanilla beans (left) are pressed by hand into a polyethylene-lined container and then sun-killed. Killed vanilla beans are then allowed to sweat (right). Reproduced with permission from Perfumer & Flavorist magazine, Allured Business Media, Carol Stream, IL.

In the oven-killing method, mature green beans are subjected to heat and high humidity in specially constructed rooms, called “calorifico”, for about 36 to 48 hours. Around 500 to 1000 beans are piled on a jute cloth or a blanket, which is rolled and covered with matting or tied with ropes to form a “malleta”. The malletas are then soaked with water and placed on shelves, lining the walls in the calorifico. The calorifico is heated with a wood-fired stove, with temperatures maintained at around 60° to 70° C, and is kept at very high humidity by pouring water on the floor. After 36 to 48 hours, the malletas are removed from the calorifico and placed in sweating boxes for an additional 24 hours to complete the killing process. Killed beans are then removed from the sweating boxes, inspected, and subjected to drying and conditioning as described Sections 6.3 and 6.4. Oven-killed Mexican vanilla beans are claimed to never “frost”, that is, they do not become covered with vanillin crystals upon drying (Theodose 1973), perhaps because surface vanillin interacts with abundant ambient moisture and is volatilized (Frenkel and Havkin-Frenkel 2006).

6.9.1.2 The Bourbon curing method

The curing method commonly used by vanilla producers in the Indian Ocean basin is the Bourbon method, named after the former French colony of Reunion, previously known as Bourbon. Madagascar is presently the main producer of Bourbon-type beans, with Reunion and the Comoro Islands producing smaller but significant quantities. In the Bourbon method, also called scalding, beans are killed by hot water immersion. Beans are placed in perforated cylindrical baskets, which are then immersed in vats containing hot water, maintained at around 65°C. Higher quality beans are scalded for about 2 to 3 minutes, while splits and beans deemed inferior, are scalded for 2 minutes or less. The metal vats, which are heated by a wood fire, have a capacity for scalding about 1.5 tons of vanilla beans in 4 to 5 hours. The scalded beans are quickly dried and while still very hot are wrapped in dark cloth or a blanket. The wrapped beans are then placed in sweating chests lined with cloth and other insulating materials. After about 24 hours of sweating, the beans are removed from the chests and dried in the hot sun for about 2 to 3 hours, rolled up in insulating cloths to retain as much heat as possible, and taken indoors to be replaced in the sweating boxes. The process is repeated for 6 to 8 days. The beans lose moisture quite rapidly and become very malleable. In the subsequent drying phase, lasting 2 to 3 months, the beans are allowed to dry slowly in properly ventilated rooms. During this time the beans are regularly sorted to remove pods that are adequately dried and ready for the next step of conditioning. For conditioning, the beans are placed for about 3 months in the air-tight chests or waxed paper lined metal containers. During this period beans are regularly inspected to ensure the development of the desired finished product. Satisfactorily cured beans are again graded according to size and quality and then bundled for shipment.

6.9.1.3 The Tahitian curing method