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CURING OF BEANS

Harvesting :
The vanilla beans mature 9 to 10 months after pollination. A green vanilla bean resembles a large green bean filled with thousands of tiny seeds. Ideally the beans are harvested when the blossom-end tips turn pale yellow. The harvested beans lack aroma. It develops only after processing or curing of beans. The longer a bean vine¬ripens, the more concentrated the vanillin and other flavour compounds are after curing. Higher vanillin content indicates better bean quality.
The beans harvested should be processed immediately within a week after harvest. They have high moisture content which has to be reduced to 22 to 30 per cent during the process of curing. Curing requires skill, experience and specialized facilities. It is generally carried out by specialist processors who purchase green beans from the growers.

Curing :
Curing of vanilla beans has been defined as their controlled ripening. It is a process of alternatively sweating and drying of beans until moisture is lost by as much as 80 per cent and the beans undergo enzymatic reactions for production of vanillin which is responsible for the characteristic flavour of vanilla.
The Mexicans developed the original, labour intensive, five to six month process for curing green vanilla beans. The process is named the "Bourbon Process", named for original name of the island of Reunion. This method takes about four to six months and is currently practiced in Madagascar, Comoro, Reunion, Uganda and India. Bourbon vanilla is considered the best processed vanilla in the world and receives premium over other suppliers. Indonesian beans were originally picked while they were still immature to avoid theft. They were using the rapid curing method of chopping the beans into 1-2 cm pieces, immersing in hot water, sweating for 72 hours and then drying them. They are now following the Bourbon method of processing. The quality of processed vanilla and vanillin content in the beans as well as their flavour depends not only on the quality of the mature bean used in processing but also the method of processing. There are four different processing techniques followed by vanilla growers in different parts of the world.

 Bourbon process:
Most of the countries use the modified Bourbon method of curing of the beans to get good quality processed beans.
Basically any curing method involves the following four stages.

1. Killing the vegetative life of the beans to allow the     onset of enzymatic reaction.
2. Raising temperature to promote this action and to     achieve rapid drying to prevent harmful fermentation.
3. Slower drying for' the development of different     fragrant substances.
4. Conditioning the product by storing for a few months.

In India, the modified Bourbon method of curing is followed to get processed beans. The curing process involves four stages as mentioned above.

Stage 1: Killing or wilting of the beans:
The mature beans are first cleaned and then sorted according to the stage of maturity and length of beans. The split beans are separated and processed separately. About 25 to 30 kg of sorted beans are taken in a bamboo basket and immersed in a broad mouthed vessel containing hot water at 68 0 Celsius. Longer beans are immersed for 5 minutes, medium sized beans for 4 minutes and small sized beans for 3 minutes. This is called scalding. Immersion in hot water stops further vegetative development in the beans and initiates enzymatic reactions responsible for production of aroma and flavour. After immersing in hot water for the required period, the beans are taken out, excess water is rapidly drained and the hot beans are rolled in a woollen blanket when still hot and kept in wooden chests lined with blankets for a period of24 hours. The temperature of water is a critical factor in killing or scalding as higher temperature deactivates the enzymes responsible for conversion of vanillin and other secondary flavour inducing components. Care should, therefore, be taken to ensure that the temperature of water does not increase more than 70 0 Celsius.

Stage 2: Sweating:

Sweating the beans involves rapid dehydration and slow fermentation to develop key flavour components. The enzymes responsible for conversion of vanillin and related compounds are most active in this stage.
The beans in the wooden chest are taken out, cleaned and spread out in the sun on dark coloured blankets or cotton cloth. This is called as sunning. The sunning area must be dry and away from roads in order to avoid     contamination with dust. The beans are kept in the sun till their temperature is around 55 0 Celsius. This can be ascertained by holding the beans in the hand. If the beans are too hot to hold, then it will have attained the required temperature. Normally this would require keeping the beans in sun for 2 to 3 or 4 hours depending on the season. It is better to expose the beans to sun for sweating on a raised platform than keeping them on the ground. A layer of agro shade net may be provided in plains to prevent excessive build up of heat on the beans. The beans should not be suddenly exposed to the sun during the hottest part of the day. They  may be kept in the sun at about 11 A. M. and then the temperature will slowly rise.
           
The beans are then rolled in the same blanket or cloth when they are still hot and kept in the sun for another     half hour and then stored in the woolen lined wooden chest. This process is repeated for 8 to 10 days. At the end of this period, the beans will have lost moisture by 40 to 50 per cent and acquire a deep chocolate brown colour. The beans will be supple and will have started to give out pleasant aroma. The beans may be slowly massaged so that β-glycosidase, responsible for conversion of glucovanillin to vanillin, which is located on the fleshy wall of the beans cone comes in contact with most of glucovanillin present in the central segment of the placental mass.
        
If sweating in sun is not possible due to inclement weather conditions, electric ovens can also be-used for the purpose. The time needed for sweating the beans in electric oven is less. The temperature in the oven may be maintained at 45o Celsius and the humidity may be increased for     faster sweating.

Stage 3: Slow drying:

The moisture content of the beans is further reduced in this stage. The moisture content of the beans will be about 50 to 60 per cent at the end of Stage 2 which will be reduced further to 25 to 30 per cent in Stage 3. The slow drying is done under shade in well ventilated room. The beans are spread on wooden trays mounted on stands in a well ventilated and open room and subjected to slow drying. In arid places, clean wet clothes are kept in the room for cooling the air and maintaining the relative humidity in the room at more than 70 per cent. The beans are dried for 15 to 20 days. They should be examined every day to ensure that moulds do not develop. The beans which have developed mould should be separated, immersed in hot water and Stages 2 and 3 are repeated. The beans may be periodically turned over for uniform drying.
 
During this stage vanillin and related compounds will continue to be formed. The slow drying process may take 15 to 20 days. Properly dried beans will normally not crack or break. They will be supple and have fully developed fragrance.

Stage 4: Conditioning:
Conditioning is an aging process necessary for flavour development. The beans are conditioned after the moisture level is brought down to desired level by slow drying process. Normally, after the slow drying process, the beans are bundled (50 to 100 beans in each bundle) according to their size or into bundles of known weight. They are then wrapped in butter paper or cellophane paper or polypropylene bags and stored in airtight containers under ambient temperature for two to three months. Conditioning is normally done at 35 to 45o Celsius. During this stage, various chemical reactions like esterification, etherification, oxidative degradation, etc., take place and a range of volatile aroma compounds are formed.
          
The beans should be examined at regular intervals during conditioning to ensure that moulds do hot develop or they are not infested with insects like mites. Vanilla beans are also subject to attack by mildews caused by Penicillin and Aspergillus, especially if they are improperly cured and have not been sufficiently dried. The mould starts from the peduncle of the beans and spreads to the entire beans. Once the beans become permeated with the odour of mould, mildew, etc., it is practically impossible to eliminate it and the value of beans is much reduced.
 Although major moisture loss in beans occurs during sweating and drying stages, it also occurs during the first three months of conditioning. Thereafter, moisture loss is negligible. Beans with an average moisture content of 32 per cent will be dark brown in colour and have a well developed suave aroma and a high degree of flexibility. They can be twisted round the finger without rupturing. They will exude pleasant aroma and exhibit characteristic luster on account of the oil contained in them. Vanillin and more than 170 related secondary aromatic chemicals will have developed in the beans. Beans with high moisture content of 50 to 54 per cent will have slightly fermented aroma and are less suave than those conditioned at lower moisture content.

         
Indian processed vanilla for international market is graded as per Bourbon grading procedure. This is in conformity with International quality standard ISO/ DIS 5565. The most desirable beans will be 18 to 25 cm long, dark brown, highly aromatic, fleshy, free from mould, insects and blemishes and somewhat oily in appearance. The complete beans and split beans are graded into four separate classes and the cut beans into a fifth class.
    
Grading of the beans is done by sorting and segregating beans which have a minimum length of 12 cm and grading them separately depending upon their color, moisture content and flavour.
 

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