From the back of the shelf comes a bag with its mouth held shut by a clip. When it was opened is long forgotten. Bring a nose close and there is still a smell. The thing to compare it with, though, went first.
What follows traces what fades first from stored tea, through a storage trial and what tea sellers publish.
The smell as the clip comes off
Take the clip off and a faint toastiness reaches the nose. The days cannot be counted; what can be told is the order of the fading.
The aroma and the look of the leaf go first, while the source of astringency barely moves. That order can be read from a trial that kept sencha for a long time.
No source measuring the days for hojicha turned up, and the sources go only as far as the order. Next comes the row of bags in that trial.
Sencha bags in a dark cupboard
In a dark cupboard, bags of the same sencha stand in a row. The worse the conditions, the faster the aroma falls.
The trial combined how well the bag kept gas out, whether the air inside was replaced, and temperature, then assessed the tea at intervals. Tea kept in a warm room in a clear bag reached its lowest point within a year. An aluminium bag slowed the fall, and chilled tea held up highest to the end.
The conclusion: chill the tea for a short stay, and for a long one combine a good bag, replaced air and the fridge. The sample was sencha, and the sources speak only to sencha's aroma. After the aroma come the compounds.
Figure 8-3-1Aroma assessment score by storage condition (sencha, out of 20)
| Storage condition | 6 months | 1 year | 18 months |
|---|---|---|---|
| Control (−80°C, gas-flushed, aluminium bag) | 14 | 14 | 14 |
| 25°C, air, transparent bag (No. 4) | 13 | 8 | 9 |
| 25°C, air, aluminium bag (No. 1) | 13 | 10 | 10 |
| 5°C, air (four bags) | 13–14 | 12 | 11–12 |
The source of astringency stays put
Tea from the same bag is brewed, and the cup is peered into. Catechins, caffeine and amino acids barely move in storage.
Even in the worst condition, the warm room, the report found no marked change. The compounds, though, were measured only partway; the final assessment was by tongue and nose alone.
And this is a result for sencha, with no promise that the same figures hold for hojicha. The authors themselves say it cannot be carried straight into practice. That is as far as the sources go. Next comes the aroma mixing with other smells.
A smell that fades, a smell that is borrowed
A bag of tea sits next to a spice jar. An aroma that fades and a smell that is taken up from elsewhere are two different failures.
The assessment vocabulary for Japanese tea lists the two as separate words. Tea held warm or left long in air carries a damp or deteriorated smell. Tea that has taken up other smells carries a transferred or foreign smell.
These words, though, were settled for storing aracha, in the assessment of sencha and gyokuro. No public vocabulary for hojicha's aroma turned up, and that is as far as the sources go. Last comes what the sellers advise.
Not the days, but the place
On the back of a shop's bag, words about where to keep it run in small print. What sellers publish leans towards the place rather than the days.
Long-established tea shops, too, list air, moisture, light and changes in temperature as things to avoid. One shop writes that it roasts just before shipping and seals the tea into small packs. None of them says how many days a freshly roasted aroma lasts.
Some give a best-before date for unopened tea, but that is a product's shelf life, not the speed at which aroma falls. The sources go as far as the order of the fading. Where to keep it is taken up in a later chapter. The figures and test conditions are gathered just below.
The numbers in detail
- Storage trial
- The storage trial is the 2013 report by Mizukami and Yamaguchi (Tea Research Journal 116). Lightly fired sencha from Yabukita plucked on 24 April 2009 was kept in the dark. Bag barrier properties, gas flushing or not, and 25°C or 5°C were combined, with standard assessment every six months.
- Aroma scores
- The aroma score is out of 20, and the tea scored 14 before storage. Tea kept at 25°C in air in a transparent bag reached its lowest point within a year. At 5°C it still scored 11 to 12 at eighteen months. The values are in Figure 8-3-1.
- Conclusion
- The conclusion is that six months calls for 5°C refrigeration, and a year calls for a high-barrier bag, gas flushing and 5°C.
- Compound tests
- The compounds (catechins, caffeine and amino acids) were measured at six months and one year. At eighteen months only the sensory assessment was done. No marked change was found even in the poor environment of 25°C in air.
- Assessment terms
- The assessment vocabulary is from “Current status and prospects of Japanese-tea quality evaluation” by the NARO Institute of Vegetable and Tea Science. It was set out for the storage of aracha, as terms for assessing ordinary sencha and gyokuro.
- Seller advice
- Maruhachi Seichajo names air, moisture, light and changes in temperature. Ippodo Tea advises keeping tea clear of sunlight, heat, moisture and strong smells. Bashoen Chaho says it roasts just before shipping and seals the tea into individual packs.
- Best-before date
- Maruhachi Seichajo gives a best-before date of three months from manufacture, unopened (chapter 7). Where to keep tea is taken up in chapter 12.