Preparation of Plant Material for Extraction
Processing of natural flavoring and color materials requires a series of individual operations, especially when preparing extractives. Two major steps, steam distillation (Chapter 7) and solvent extraction (Chapter 8), are dealt with later. Some of the other operations are briefly mentioned in this chapter. There are many theories, finer details, and modifications that are needed in these operations when it comes to application to a specific product. Therefore, readers are advised to refer to specialist books and articles if an in-depth understanding is required.
Almost all plant materials, whether for use as such or for making extractives, require drying. A few exceptions are when extracts with fresh flavor or with a water-soluble colorant such as anthocyanin are required. Drying ensures protection from spoilage. It also helps to break down the cells, enabling active components to be released when steam or a solvent is applied. The bulk of these materials, especially in the tropics, are sun dried. A few materials are dried in a dryer where previously heated air is passed through the material by either cross-flow or through-flow. Normally, drying is carried out as part of the agricultural operation or in premises close to the growing area. The processors of extractives buy the dried material. In some rare cases, the processor has to do some finishing of the drying process using either sunlight or a dryer.
In rural areas, smoke drying is not uncommon, but this is not a desirable option as smoke can affect the flavor. Natural flow hot pipe drying rooms are often used for crops such as cardamom, when an assured electricity supply is not available. The ideal drying process is achieved when the previously heated air is obtained using a heat exchanger.