CFW Projects supplies drying equipment for drying herbs, spices and other speciality products. Since ambient conditions, product requirements and costs can vary widely, different types of drying equipment are used. CFW can advise producers on the appropriate dryer and supply the necessary equipment, integrating it into the production line. For herbs and similar items, convection drying and heat pump dehumidifiers are two of the more common technologies.

About Herb Drying

The use of dried specialty crops has diversified in recent decades in accordance with the trend towards more natural or organic food products and alternative medicines. This has led to growing interest in farming and processing these crops. The specialty crop market is considered to include herbs, spices, lentils, mustard seed, canary seed and others.

As with any other plant material, herbs can spoil or suffer other forms of degradation over time. Large producers can suffer correspondingly large losses as a result. A variety of preservation techniques have been used, but drying the product remains perhaps the most economically feasible means of increasing product shelf life and reducing transport and storage costs. Smaller-scale producers often use darkened drying rooms, but the labour costs and time involved are prohibitive for industrial production.

Usually, herb drying is done by heating the product. During this process moisture evaporates from the surface. The moisture remaining in the interior diffuses towards the surface as a vapour pressure gradient is created between the interior and the surface.

While heating is an effective drying technique, the market value of herbs and niche crops depends on properties that are usually heat-sensitive. These may include appearance, aroma and flavour, and nutritional, nutraceutical and pharmacological properties. Overheating the product through inappropriate drying techniques can reduce quality substantially. At the same time, drying at lower temperatures can lead to longer drying times and consequently higher energy costs. Evenness of drying is also important, as it ensures that the entire product batch is dried on schedule without unduly affecting product quality in part of the batch.

The capital and operating costs, maintenance, capacity, and safety of the dryers to be used, as well as their ability to produce a high-quality product, must be considered. Process management and ease of use are also important. By selecting a custom product where these factors have been taken into account during the design stage, the most appropriate solution can be found.

In some cases a hybrid system using more than one drying technology is the best solution. The use of recirculation heat pumps together with convection drying systems is one example. These systems can often reduce drying times and improve efficiency compared to using only conventional convection heating, but cost somewhat more. Intermittent application of heat may also be possible in some cases to prevent overheating. The use of gas-fired heating and dehumidifiers has increased for specialty crop drying applications in recent years.

It must be borne in mind that process management is essential to producing good results. Separating different plant parts and species with different drying kinetics before drying will help to prevent uneven drying.