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Tea and Herb Drying

CFW is an established and reputable supplier of air technologies for the food industry. We produce fans and ventilation systems, including reversible impeller designs suitable for tea withering and herb drying. We also assist with fan selection for fast and cost-effective drying and supply humidifiers and dehumidifiers. Contact us for more information or look at our dehumidifier product list at www.dampcontrol.co.za.

tea plant

Drying tea preserves the product, halting enzyme activities and reducing moisture content to 2-3%. The required drying capacity of dryers can vary markedly, as much moisture may already have been lost by the time the leaf reaches the dryer due to processes collectively known as wither. Tea may be dried either by air drying or by baking. For black tea, a bed plate is used to contain the leaves and a fan and heater force hot air through them. Studies suggest that the best drying temperatures for black tea are around 100 °C and acceptable ranges are from 80° to 110 °C, although higher temperatures are acceptable if the time that leaves are in the dryer are short. Drying temperatures should not be too low at the start of the process; otherwise the continued enzyme activity will lead to quality deterioration, while high temperatures reduce caffeine content.

Medicinal and culinary herbs and tisanes are also sold dried. Although drying rooms and sheds are often used for small operations, such practices are highly labour-intensive and not suitable for large crops. The use of a forced-air drier is preferred for industrial-scale production to preserve flavour, colour, essential oils and/or medicinal properties. Good air circulation is needed for this since it allows for drying at lower temperatures and reduces drying time, thus preventing the degradation of heat-sensitive desirable substances in the product which cause them to have higher market values. Reliable temperature control and high air flow throughout the plant matter is thus critical. The type of plant, part of the plant used, and ambient conditions will affect drying times and temperatures. Hot, humid outside conditions require higher drying temperatures, though low temperatures are preferred.

Selecting a dryer depends on the expected size of harvests. Dryers should preferably be able to handle an entire harvest quickly enough to prevent spoilage. Efficiency and capital costs should also be taken into account; commercial herb dryers can be quite costly. The use of gas-fired dryers and commercial dehumidifiers has become more common for even and reliable drying.

Desiccant drying of herbs and flowers has also gained popularity. Herbs such as rosemary, thyme and parsley are some of the herbs that have proven results when dried by this method. Silica gel, borax, alum and cornmeal are all used as desiccants in the industry. Desiccant dehumidification produces final products with excellent colour, texture and durability.

Herb stems and leaves need to be dried until a piece “snaps” when broken. Roots should not be dried at too high a temperature; this could result in case hardening, sealing in moisture which could lead to mould and a poor-quality, unmarketable product. Roots can be dried at a low, constant temperature while aerial parts should be dried at higher initial temperatures that are later decreased. This helps maintain the green appearance of dried stems and leaves.