hiire / hi-ire / firing / roasting of Japanese green tea

Non-oxidized tea
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teatray
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Tue Dec 14, 2021 10:09 pm

Summarizing some info I found on this interesting topic. Maybe it's useful as a starting point for others. Would love to get corrections and additional info.

Firing (火入れ / hiire / "putting in fire"), also known as (pan) roasting, baking, (final) drying, refining, is one of the final finishing steps in Japanese green tea production (sencha, kukicha, gyokuro, kabusecha, steamed tamaryokucha, but not matcha, not sure about kamairicha). It may take place at the tea producer (esp. if they have direct retail channels), at a wholesaler (usual case), or be specially arranged by a wholesale buyer who may e.g. wish to buy raw tea from one place but fire elsewhere (or sometimes not fire traditionally at all, though perhaps use other means to reduce water content).

It's usually done at 100-120°C in specialized equipment, of which there is a large variety (hot air tray dryers, large drums machines). The goal is to reduce water content from around 5% in cold-stored raw tea (a.k.a. aracha, roughly corresponding to Chinese mao cha), to around 2%-3% in the finished product. This not only makes the product shelf-stable for the consumer, but also brings out the sweetness and nutty notes and (depending on the equipment used) imparts the "roast scent" (hiire-ka).

How exactly it's done depends on the manufacturer and also the wishes of the wholesale buyer. Most buyers apparently operate under the assumption that each region in Japan has a set preference for firing level.

I imagine the exact details of the process are trade secrets. It can be done before or after sorting and shaping (pre-/post-roasting). Post-roasting seems to be state-of-the-art, as you can fine-tune the roasting parameters according to the raw material (leaves, stems of different grades). Some of what has been separated before is often mixed back together after firing, creating the usual commercial grades (but the buyer can specify an exact mix, e.g. 100% stems would be kukicha, 100% leaves would be pretty fancy).

Hiire is part of shiage, which encompasses all finishing steps from aracha to saleable product (incl. sorting and shaping). Some products (gyokuro, esp. from Uji, some shincha) may undergo a lighter firing (depending on region/manufacturer). Other regions (e.g. Saitama prefecture) are known for their strong hiire / hiire-ka (Sayama hiire). No firing at all is also possible but rare, see e.g. Florent's 2015 blog post, mentioning an innovative gyokyuro producer, or Hojo's detailed treatment of the subject, also comparing Japanese vs Chinese trends. Apparently, it's possible to "re-hiire" an old (cold-stored) tea to refresh its taste.

Sources / further reading:
  • Florent has an informative blog post from 2020 about the refining steps, equipment, etc.
  • Shizuka Maitani has a wonderful 2014 video of some kind of guided factory tour.
  • The producer may fire Shincha differently.
  • Florent also has a 2013 post comparing two differently fired but otherwise almost identical fukamushi.
  • Two similarly-titled posts covering the subject (first, second) on Ricardo's blog
  • Mei Leaf has a 2017 video that talks about this processing step (but keep in mind it's sprinkled with inaccuracies on other topics I know a bit more about, so maybe the firing info isn't spot on either)
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