How much work does it take to describe the aroma rising from a cup in the names of compounds? From a researcher’s perspective, it is a long process of separating, smelling and counting.
Reports from 1973 onwards trace ways of extracting aroma and examining it with human noses and chemical analysis. For each, we look at what was used, what was measured and how far the conclusions extended.
In 1973, a list of 21 pyrazines
According to a review by the Industrial Research Institute of Ishikawa, Yamanishi and colleagues compared aroma compounds in green tea with those in hojicha roasted at 200°C for several minutes. In 1973, they reported 21 pyrazines in hojicha and substantial increases in those compounds through roasting. In the same year, Hara and colleagues reported that hojicha contained many pyrazines, pyrroles and furans formed during roasting.
A 1999 paper also recounts that Yamanishi and colleagues identified 66 compounds in hojicha aroma. The broad outlines of that aroma had already been drawn half a century ago.
Change the extraction method, and the compound list changes
The 1999 paper describes drawbacks in the SDE and reduced-pressure distillation methods previously used to prepare tea aroma concentrates: water-soluble volatile compounds were difficult to recover, and components in the leaves could change during sample preparation. It judged these methods unsuitable for investigating the aroma pattern encountered when drinking tea, and instead extracted the infusion with an organic solvent.
When the National Agriculture and Food Research Organization (NARO) examined roasted tea, it obtained 0.1 mL of aroma extract from 200 g of tea using reduced-pressure and high-vacuum distillation, then diluted it 10-, 100-, 1000- and 10000-fold with dichloromethane. In the Industrial Research Institute of Ishikawa’s bōcha research, a stir bar was placed in the extract to adsorb compounds, which were then released by heating. For comparisons among commercial products, compounds were collected for 30 minutes from the air in a vial containing 0.5 g of ground tea warmed to 80°C.
The question is not simply which method is right: the methods differ in what they can extract. Reading a list of compounds also means considering the extraction method that produced it.