Review on drying methods for herbal plants

Herb drying is a common stabilization technique in preserving vital qualities of essential oil yield and bioactive compounds. However, systematic and appropriate drying methods are still not sufficiently investigated. This review focused on drying herbal plants and how drying affects essential oil yield, antioxidant content, antimicrobial activity, health benefits, colour, and aroma of dried goods. Various drying methods are summarized. Preferable drying methods for most herbs are oven and freeze-drying, but this is dependent on the type of heat transfer onto the herb's surface biostructure and constituent volatility. However, herb colour retention requires a faster drying time. Furthermore, antimicrobial and pharmaceutic compounds require a focused study due to their unique properties, which cannot be determined by a general drying method. Because there is no universal drying method, these findings emphasise the importance of comprehensive herb research. However, a specific drying pattern can be observed, enlightening future research and drying innovations.