Teacology

Tea, with an Ecological Approach

Oxidizing Herbs Like Black Tea or Oolong Tea

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This is inspired by my original posts Oxidizing Herbs like Black or Oolong Tea and Sage Tea made like Black Tea.

Oxidation is one of the key aspects of tea production.  Usually, oxidation is presented as being the main characteristic that distinguishes black teas (which are oxidized) from green teas (which are unoxidized).  Since writing my original post, I have learned a lot more about tea production, and I have researched and compiled a page on the oxidation of tea on RateTea.  This page goes into more depth, explaining how a lot of the ways in which the topic of oxidation is presented are oversimplifications.  If you want to learn more about this process, I recommend visiting that page.

This page is about something different: using an oxidation process similar to that used to produce black teas to process the leaves of other plants.

Herbal Teas Are Generally Not Deliberately Oxidized: A Few Exceptions

In many respects, herbal teas are often considered analogous to true teas from the Camellia sinensis plant.  Yet there is one key difference: the herbs used to produce most herbal teas are rarely oxidized.  Instead, most herbs are usually just collected and dried.  This process makes them most similar to white teas, which are the least processed of teas on the market.  The modest amount of oxidation that happens to these herbs is an unintended consequence of the drying process, not an intentional and essential part of processing.

Loose chamomile flowers in a spoon

Chamomile, like many herbs used in herbal tea, is gathered and dried without any additional processing to induce oxidation.

There are several notable exceptions to this trend.  Rooibos and honeybush, both referred to as South African red tea, are both produced through a process that involves oxidation, which can be interpreted as making them somewhat distant cousins of black tea.  Incidentally, rooibos is often discussed as being among the most “tea-like” of herbal teas, and this similarity in production may explain why.  The process used to oxidize rooibos and honeybush, however, is quite simple, involving collecting the leaf and letting it sit in heaps outdoors–less of a controlled process than tea goes through, but achieving similar results.

The following image is licensed under the Free Art License, courtesy of Wikimedia Commons:

Red rooibos leaf on a white background

Rooibos is traditionally oxidized during its production, turning it red, much like how black tea turns a dark color.

Yerba mate and Guayusa, the caffeinated herbal teas produced from species of holly plant native to South America, also are processed in a bit of a more involved way, although not necessarily one involving oxidation.  Often, the leaves are dried and aged, and then roasted, however, there are also un-aged and un-roasted versions on the market.  There is, however, a case of people processing Yerba mate more like tea, the Premium Yerba Mate Buds sold by Upton Tea.  But this sort of endeavour is very rare.

Being curious, however, I repeatedly asked myself the question: why don’t more people try to process herbs like black tea?  It may be difficult to get good results from such a project (I wasn’t a huge fan of the Yerba mate buds described above) but I at least wanted to try.

My Experiment: Oxidizing Common Sage, Lemon Balm, and Other Herbs

Some time ago, in the fall of 2009, shortly after launching RateTea, I became fascinated by the idea of applying a similar production process to herbs, to the one usually used to make black tea.  I tried this out on a few herbs, including common sage, Monarda sp. (Bee Balm, Wild Bergamot, Oswego tea), lemon balm, and various mints.

I experimented with a number of different attempts on the different herbs, but they all involved picking the leaf and bruising it shortly after harvest (before it dried out), and then allowing it to sit in a damp area until the leaf turned completely dark (this took a matter of hours).  To do this, I placed the leaves on a plate with a damp cloth over them, and stored them in a cool, dark area.  After the leaf was fully oxidized, I then heated the leaf very slightly using a toaster oven.

Trial and error taught me that, with tougher leaves like sage, extensive bruising is needed to ensure full oxidation.  The first few batches I attempted came out with splotchy oxidation.  With the tougher herbs, like common sage, I ended up using a rolling pin on a hard surface to crush the leaves.

Here is a photo from one batch of common sage, Salvia officinalis, where I had tightly twisted and rolled the leaf:

A teacup with dry rolled up leaves in it

Leaves of common sage (Salvia officinalis) which have been bruised and allowed to oxidize similarly to black tea.

It was fun to see how the leaf can be formed into different shapes.  These leaves looked similar to a Ceylon Oolong tea, unfortunately discontinued, Shanti Tea’s Thousand Arrows.

The result of this process, flavor-wise, was also promising.  The oxidation seemed to improve the flavor and aroma of the sage, for drinking, as sage can be a bit dominating and harsh.  The other herbs also worked well, although some were better than others.  The best result in terms of flavor was lemon balm.  As I noted in my original post, lemon balm yielded the batch that came out most like black tea, and it had some floral tones that are absent in the straight dried herb, and was also more vegetal, but was less lemony.  Apple mint and the Monarda also yielded good results.

What do you think?

I would love to try this again some time soon.  I am still curious to know if anyone else has ever tried this sort of project.  I did not get any comments on my original post, as it was from before I had developed much of a following for my blog.  I would be especially interested to learn of attempts by people who have had some experience in or first-hand exposure to tea production.

Some questions for you:

  • Do you find this idea as intriguing as I do?
  • Have you ever tried processing any herbs in this manner, so as to encourage oxidation, or do you know anyone who has?
  • Whether or not you have ever tried this, do you have any advice or suggestions about processing, perhaps from knowing a bit more about tea production than I do?
  • Do you have any suggestions of herbs to try?
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Author: Alex Zorach (teacology)

I am the founder and editor of RateTea, and am also a co-founder at Why This Way. I am committed to sustainability in every aspect of my life. I like describing my approach to life as "ecological" because it is both scientific and holistic.

14 thoughts on “Oxidizing Herbs Like Black Tea or Oolong Tea

  1. Great post, Alex – and yes, I’d love to learn more about this topic. I’ve never tried it, or thought of it for that matter, but I’m very intrigued! Happies of holidays to you.

  2. I too find this idea intriguing. I have not tried it but will definitely plan to in the future. I have mint that grows in my backyard and I may try it with that.

  3. Been experimenting with some basics like mint and cat mint. Too early to know what the results will be but I stumbled across your website. Nice to know I am not the only who has been thinking about this.

  4. I was beginning to think I was the only one who had the magnificent idea of oxidizing herbs like tea and rooibos. Yesterday I made a batch of stinging nettle tea. I ran the wilted leaves through a blender at low speed, oxidized for around 5 hrs and dried in a pot on the stove with stirring and swirling. The finished product had a dark brown/greenish color. The brew was a beautiful light brown/golden color as opposed to a decoction of the fresh green leaves which gave a pale yellow green color. It was drinkable, and much more complex than the untreated tea. It did however have a very distinct hay/herbaceous smell, which put me off a bit. Have you experienced this smell in any of your teas? I’m going to try running the leaves through a meat grinder next time. I hope this will mimic the CTC-process used in tea processing. I wonder if the final roasting could help remove or reduce the undesireable flavour characteristics. The ultimate aim of this project os to produce wine from the tea. “Oxidized stinging nettle tea wine” quite a mouthful. I hope to hear from you soon.

    Happy steeping
    Villiam

    • Hmm, this is interesting; I’ve never tried oxidizing nettle tea in this way, but I have tried nettle tea. I’ve usually seen nettle tea dried (and consumed it in this form, after steeping it), and it seems partially oxidized from the look of the leaf and the darker color of the brewed cup. And I do find it tends to have a strong hay and herbaceous smell, like you described.

      I have never found other herbs to have this quality though, in my experiments oxidizing them. If anything, I find these smells are diminished somewhat by the oxidation process in other herbs. I tend to get less aromas like straw or hay or vegetables when I oxidize the herbs more. I suspect that that quality is just something peculiar to the nettle. When I compare green to black teas, or green rooibos to red rooibos, it is the less-oxidized forms that tend to have more of a straw or hay aroma.

  5. Fascinating idea. I wonder how the oxidation process affects the medicinal qualities of the herbs. Perhaps a TCM herbal specialist would know? I’d be curious how this would work with Jiao Gu Lan (gynostemma), also called Southern Ginseng, one of the Chinese adaptogens.

  6. Great post, and, I’d love to learn more about this topic. I am trying to grow herbs in my backyard. So thank you so much.

  7. Hi there. Once you’ve oxidised the leaves, how do you dry them? Kind regards, Alex

    • Hello other Alex!

      There are many different ways of drying. I usually put them in a warm, dry, well-ventilated area away from sunlight. Sunlight can make herbs dry out faster, but it can degrade the aroma and flavor. Often it’s easy to hang them somewhere, if they’re intact and on the stems. When I dry herbs without an oxidation step, I’ve sometimes put them in a brown paper bag, on the stem, and hung them up to dry. When I’ve oxidized herbs, though, they haven’t been intact, so I often lay them out flat on a sheet of paper, like a brown paper bag or paper towel.

      You can also dry herbs in an oven, or by heating them in a pan. These definitely alter the herbs–and are likely to impart a toasty flavor if the temperature is high enough. (Even very low temperatures in ovens still will impart a toasty flavor.) A lot of traditional green teas are processed by means like this, pan-firing or baking.

      Heating stops the oxidation process, so it can be used to control the level of oxidation…a lot like how oolongs can be partially oxidized. I haven’t ever gotten this complex though…but I’d imagine that if people fiddled around with it they might get some interesting results.

  8. In my area there is an abundance of sweetfern (Comptonia peregrina) in the opening of larger forests. Today I dried a simple infusion of the dried leaf and found it not dissimilar to green tea. I think I will try some process of oxidation to see how much I can manipulate the flavor. Thanks a lot for an excellent post.

    • I’ve never heard of anyone brewing up an herbal tea from sweetfern, I can see this working beautifully…sweetfern has such a wonderful fragrance! I love smelling the leaves when I walk by it growing in nature or in landscaping.

  9. Yes, I’ve done this for several years and the results can be dramatic, especially with the mints and rose family. Not a big change for sage and holy basil though.

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