Artificial methods are employed to cure vanilla. Vanillin is developed as a result of the enzyme action on the glycosides contained in the beans during the process of curing. Basically any curing method involves the following four stages: 1. Quality Requirements 2. Traditional Curing Methods 3. Mexican Curing Methods 4. Bourbon Curing Method.
1. Quality Requirements:
The primary quality determinant for cured vanilla beans is the aroma/flavour character. Other factors of significance in quality assessment are the general appearance, flexibility, the length and the vanillin content. The relative importance of these various quality attributes is dependent upon the intended end-use of the cured beans.
Traditionally, the appearance, the flexibility and size characteristics have been of importance since there is fairly close relationship between these factors and the aroma/flavour quality. Top quality beans are long, fleshy, supple, very dark brown to black in colour, somewhat oily in appearance, strongly aromatic and free from scars and blemishes.
Low-quality beans are usually hard, dry, thin, brown or reddish-brown in colour and possess a poor aroma. The moisture content of top grade beans is high (30 to 40 per cent), whereas it may be as little as 10 per cent in the lower grades. At one time, the presence of a surface coating of naturally exuded vanillin crystals (‘frosting’) was regarded as an indicator of good quality, though this is no longer considered so.
2. Traditional Curing Methods:
A number of procedures have been evolved for the curing of vanilla but they are all characterised by four phases:
(a) ‘Killing’ or Wilting:
This stops further vegetative development in the fresh bean and initiates the onset of enzymatic reactions responsible for the production of aroma and flavour. Killing is indicated by the development of a brown coloration in the bean.
(b) ‘Sweating’:
This involves raising the temperature of the killed beans to promote the desired enzymatic reactions and to provoke a first, fairly rapid drying to prevent harmful fermentations. During this operation, the beans acquire a deeper brown coloration and become quite supple, and the development of an aroma becomes perceptible.
(c) Slow Drying:
The third stage entails slow drying at ambient temperature, usually in the shade, until the beans have reached about one-third of their original.
(d) Conditioning:
In the final stage, known as ‘conditioning’, the beans are stored in closed boxes for a period of three months or longer to permit the full development of the desired aroma and flavour. The two most important of the various traditional procedures for curing vanilla beans are those of Mexico and the Indian Ocean islands producing ‘Bourbon’ vanilla.
3. Mexican Curing Methods:
The two main traditional forms of curing employed in Mexico are the sun-wilting and the oven-wilting procedures. The former is the oldest known method of curing and the latter was introduced around 1850. Both methods are still widely used by the specialist curing firms in Mexico which process the vast bulk of the vanilla crop. The harvesting period in Mexico extends from November to January and curing by either method takes around five to six months before the product is ready for the market.
‘Sun-wilting’ – On arrival at the curing house, the fresh beans may be set aside in a store for a few days until required and during this time the beans start to shrivel. The fresh beans first have their peduncles removed and are then sorted according to their degree of maturity, size and into un-split and split types. This is done as the various sorts cure at different rates. Beans, which are already beginning to darken, are removed, wiped with castor oil and are cured separately.
The beans are killed by exposing them to the sun for a period of about five hours on the day after sorting. The fresh beans are spread out on dark blankets resting on a cement patio or on wooden racks. In the afternoon, the beans become too hot to hold by hand and are then covered by the edges of the blanket. In the mid-to late afternoon before the beans have begun to cool, the thick ends of the beans are laid towards the center of the blanket and rolled up.
The blanket rolls are immediately taken indoors and are placed in blanket-lined, air tight mahogany boxes to undergo their first ‘sweating’. Blankets and matting are placed over the sweating boxes to prevent loss of heat. After 12 to 24 hours, the beans are removed and inspected. Most of the beans will have begun to acquire a dark-brown colour indicating a good ‘killing’.
Beans which have retained their original green colour or which have an uneven coloration are separated and are subjected to oven-wilting. Those beans, which have been properly killed, are next subjected to a process involving periodic ‘sunning’s’ and sweating’s. ‘Sunning’ entails spreading the beans on blankets and exposing them to the sun for two to three hours during the hottest part of the day when weather conditions are favourable.
During the remaining part of the day, unless a sweating is to be undertaken, the beans are stored indoors on wooden racks in a well- ventilated room. There are two distinct phases to this sunning/sweating stage. The first phase involves a fairly rapid drying in which the beans are given ‘sunnings’ virtually every day and several overnight sweating’s until they become supple. This takes about five to six days.
A preliminary sorting into lots corresponding to the various grades is usually carried out at this juncture. This is followed by further ‘sunnings’ and additional but less frequent sweatings. In practice, ‘sunnings’ are not carried out every day in this second phase since, apart from constraints imposed by the weather, too rapid-drying is considered to be detrimental to quality.
Some 20 to 30 days after killing, most of the beans become very supple and acquire characteristics close to those of the final product and are ready for the next stage of very slow drying indoors. The total number of sweatings undertaken during the ‘sunning/ sweating’ operation can vary between four and eight. Those beans, which require a large number of sunnings and sweatings generally, provide a low-quality product.
Very slow drying indoors lasts for approximately one month and a further sorting into grades is usually carried out during this time. The beans are regularly inspected and those, which have achieved the requisite state of dryness, are immediately removed from the racks for ‘conditioning’. The overall sweating and drying operation may take up to eight weeks from the time of ‘killing’, according to the prevailing weather conditions.
Small and split beans are usually ready for conditioning earlier than perfect, large beans. Beans removed for conditioning are sorted again and are straightened by the fingers. This operation is also useful in that it spreads the oil, which exudes during the curing process and gives the beans their characteristic luster. The beans are next tied into bundles of about fifty with black string.
The bundles are wrapped in waxed paper and are placed in waxed paper lined, metal conditioning boxes. Conditioning lasts for at least three months and during this period the beans are regularly inspected. Mouldy beans are removed for treatment and those, which are not developing the required aroma may be re-subjected to ‘sunnings and sweatings’.
At the end of the conditioning period, the beans are given a final grading and are packed for shipment. ‘Oven- wilting’- In this procedure, use is made of a specially constructed brick or cement room, known as a calorifico, which serves as an autoclave.
The room measures approximately 4 x 4 x 4 metres and incorporates a wood- fired heater, which is stoked from the outside. It is fitted with a small access door and has wooden racks fitted along the walls. The beans to be killed by this method are divided into piles of up to 1000 and are then rolled up in a blanket, which is finally covered with matting to form a malleta.
The malletas are moistened with water and are placed on the shelves in the calorifico. Water is poured onto the solid floor to maintain a high humidity, the door is closed and the heating fire is lit. In about 12 hours, the temperature inside the calorifico reaches 60°C. After a further 16 hours, a temperature of 70°C is attained and this is maintained for another 8 hours. The malletas are removed after a total of 36 hours in the calorifico.
If the temperature cannot be raised above 65°C, then the total period of autoclaving is extended to 48 hours. On removal from the calorifico, the matting is quickly stripped from the malletas and the blanket wrapped beans are placed in sweating boxes. After 24 hours, the beans are removed and inspected.
The killed beans are then subjected to repeated sunnings and sweatings, described above under ‘Sun-wilting’. Should the weather be overcast, the killed beans are stored on racks indoors in a well- ventilated room until sunning is possible. However, if the weather does not improve within three days, the batch is reprocessed through the calorifico and sweating box.
4. Bourbon Curing Method:
Bourbon vanilla is the name given to the product from the former French possessions in the Indian Ocean, which employ a curing technique first developed on the island of Reunion, formerly known as Bourbon.
Production of Bourbon-type vanilla is now dominated by Madagascar, with the Comoro Islands and Reunion as smaller but important sources. The Bourbon curing technique is distinguished from those of Mexico in that ‘killing’ is achieved by scalding the beans in hot water and fewer sweating’s are undertaken.
The Bourbon product usually has higher moisture content than the corresponding Mexican grade and is frequently frosted. As in Mexico, curing of vanilla is carried out by specialist firms rather than by the vanilla growers.
Slight variations in the curing technique are practiced in the various producing islands and the following is a description of the procedure evolved on Madagascar. On arrival at the curing factory, the beans are sorted according to the degree of maturity, size, and into split and un-split types.
Batches of beans, weighing 25 to 30 kg, are loaded into openwork cylindrical baskets, which are then plunged into containers full of hot water heated to 63 to 65°C over a wood fire. Batches of beans, which will eventually make up the top three qualities, are immersed for 2 to 3 minutes, while smaller and split beans are treated for less than 2 minutes.
The warm beans are rapidly drained, wrapped in a dark cotton cloth and are placed in a cloth-lined sweating box. After 24 hours, the beans are removed and inspected to separate those, which have not been properly killed.
The next stage of sun-drying is carried out on a plot of dry easily drained ground, at some distance from roads to avoid contamination by dust. The killed beans are spread out on dark cloths resting on slatted platforms, constructed from bamboo and raised 70 cm above the ground. After one hour of direct exposure to the sun, the edges of the cloth are folded over the beans to retain the heat.
The cloth- covered beans are then left for a further two hours in the sun before the blanket is rolled up and taken indoors. This procedure is repeated for 6 to 8 days until the beans become quite supple. The third stage involves slow drying in the shade for a period of 2 to 3 months. The beans are spread on racks, mounted on Supports and are spaced 12 cm apart in a well-ventilated room.
During this slow drying operation, the beans are sorted regularly and those which have dried to the requisite moisture content are immediately removed for conditioning. In some localities in the Bourbon producing areas, where the weather is frequently inclement during the sun-and indoor-drying periods of curing, ovens set at 45 to 50°C have traditionally been used. Conditioning of the beans is carried out in a similar manner to that described for Mexico and takes about 3 months for completion. The overall curing process for Bourbon vanilla lasts for 5 to 8 months (from June to early October).
A modification to the traditional Bourbon curing method was devised in Puerto Rico in the 1940s and was adopted by the vanilla co-operative at Castaner. On arrival at the factory, the beans are sorted into split and un-split types and are then killed as soon as possible.
Prior to killing, the beans are wiped with a damp cloth. Scalding entails three 10-second immersions at 30-second intervals in a water bath at 80 °C. After draining, the beans are wrapped in a blanket and are placed in a sweating box.
Killing is followed by daily two-hour sunnings and overnight sweating’s for about seven days until the beans become supple. The next stage of indoor air-drying is continued until the beans reach one-third of their original weight.
The beans are then bundled and conditioned in tin boxes until they dry to one-quarter of their original weight. By contrast to Bourbon vanilla from the Indian Ocean producers, Puerto Rican vanilla scalded at 80 °C rarely frosts. When the weather is unsuitable for sunning, the beans are sweated in a closed oven at 45°C containing a pan of water.
Other methods for V. fragrans – The Guadeloupe technique entails killing by making scars with a pin along the faces of the bean and then exposing the beans, wrapped in a blanket, to the sun for a few hours. The pin, which should be sterilised regularly, is fitted into a cork to protrude no more than 2 mm. After killing, the curing process is similar to that of Mexico. Two other methods, which tend to provide a poor-quality product, are the ‘Guiana method’ and the ‘Peruvian process’.
The ‘Guiana method’ involves killing the beans by placing them in the ashes of a fire until they begin to shrivel. On removal, the beans are wiped clean, rubbed with olive oil, the lower ends are tied with string to prevent splitting, and they are then left to dry in the open air. In the ‘Peruvian process’, the beans are killed by immersion in boiling water and are then tied at the ends and hung up in the open air.
After drying for about twenty days, the beans are lightly smeared with castor oil and are tied in bundles a few days later. No distinctive local method of curing appears to have been evolved in Java. Modifications of the Mexican and Bourbon methods were commonly used but in general less care seems to have been taken in curing and grading. The quality of the Java product has never compared favourably with those of Mexico or the Bourbon producers.