For centuries, herbs were preserved by hanging or lying them in shade in an area with good air flow.
In the last few decades, as we’ve become less willing to wait for nature to take its course, we turned to forced air dehydration. Many of us have dehydrating machines in our homes and have used these for herbs as well as fruits and vegetables.
Herbalists sometimes use large machines – or rooms/sheds with forced air heat, ventilation, and dehumidifiers – to quickly dry larger volumes. Drying rooms must be maintained at a specific temperature and humidity (temperatures > 90-100 degrees degrade herbs), which can be difficult to control, especially when it is hot/humid outside. The hotter the conditions, the more the volatile compounds in the plants evaporate. It’s the old quality versus quantity conundrum. But, when you grow in small amounts, there’s no need to sacrifice quality.
Recently, some of us turned to freeze dryers to prevent degradation caused by heat,
while still providing a quicker product. Have you ever wondered why beautiful green herbs turn brown in a dehydrator? This is due to the breakdown of pigments such as chlorophyll due to heat. Air drying is far less likely to cause this problem, and freeze drying has no significant impact on chlorophyll, which is why these herbs retain their bright green hues. In pilot studies, freeze drying was found to preserve the medicinal effects of a plant most effectively.The problem is that freeze drying is expensive – the equipment itself costs thousands of dollars. This puts it out of reach for most home growers.
When I am asked for a recommendation on preserving herbs at home, I recommend air drying. Often the response I get is, “But isn’t dehydrating better?” The answer is a resounding “no!” A lot of advertising money has been spent convincing us we need the best dehydrator possible, so it’s easy to understand the confusion.
Air drying is second only to freeze drying in terms of herb preservation.
That is simply because this method – just like what our ancestors used – does not apply heat, so it does not degrade the herb. As long as there is good air flow, and a clean space for drying, this is by far the best way to preserve your herbs. Studies have looked at deterioration of color and antioxidant or vitamin content of foods and found that using dehydrators or drying rooms degrades the plant or food. Air- or freeze-drying conserves the functional compounds found in the plants we use for herbal teas and other herbal products far better than heat-based dehydration.
One look at the herbs explains why many herbalists are transitioning to freeze drying.
The color is bright, the aroma sharp, and they are bursting with flavor! This allows herbalists to provide higher quality, better tasting herbs and tea blends, with higher percentages of the good stuff that’s in the plants. It’s a matter of quality – for the best nutrition and flavor-filled “bang for your buck,” freeze drying is absolutely the way to go in a professional situation.
At home, simply air dry – hang or place herbs flat to dry on screens in a clean space,
keep them well separated and labeled. Make sure there is steady airflow, and carefully rotate herbs as they are drying to ensure good air contact with the surface area of the plants. Once the herbs are completely dry, give them time! Store in a sealed Mason jar or vacuum locked container away from sunlight and temperature extremes. Never store herbs in plastic, and avoid use of glass if you’re leaving the herbs out on your kitchen counter, as light and plastic are enemies of preserving high quality herbs.
Grant Thamkaew, IngegerdSjöholm& Federico Gómez Galindo (2021) A review of drying methods for improving the quality of dried herbs, Critical Reviews in Food Science and Nutrition, 61:11, 1763-1786, DOI: 10.1080/10408398.2020.1765309
Haizhu, Z., Zheng, L., Zhang, X., Cui, X., Wang, C., & Qu, Y. (2020). A study of the freeze-drying process and quality evaluation of Angelica sinensis. International Journal of Food Engineering, 17(6), 411-422.
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