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CQC 1.06 Roasting Defects Part 2

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Raw Beans, Scorched Beans — or Both?

Two detailed studies have attempted to establish which volatile aromatic compounds are ‘markers’ for five separate roast defects: light, dark, scorched, baked, and underdeveloped. Some roasters may debate the appropriateness of the roast profiles that were used in establishing the reference roasts used in these studies (Giacalone et al, 2018 and Yang et al., 2016). However, one thing is very clear: The scorched and dark roast from this research had a clear predominance of the chemical 4-ethyl-2-methoxyphenol, as well as phenol. Phenol is considered to taste smokey  (Flavent, 2002). The profiles that produce under-roasted coffee, e.g. the excessively light, underdeveloped roasts, have a predominance of indole (Yang et al., 2016). One type of indole is found in kale, broccoli, asparagus, and brussels sprouts. 

To simplify the complex theory of coffee roasting, if the coffee tastes raw like vegetables, it’s manifesting an under-roasting taint, and if it tastes burnt and smoky, it’s manifesting an over-roasting taint. It’s also possible that a coffee may exhibit both a vegetal flavour and a burnt flavour. At BH we tend to refer to the under-roasted roast defect as the raw defect. BH founder and CEO Matter Perger says,

“Raw and scorched roast defects could occur in a very short roast where the roasting drum is excessively hot. The outside of the beans will scorch whilst the inside of the beans could still be raw. It could also happen in a roast that experienced a rapid increase in temperature at the end of the roast. In both these cases, there will be a large difference between the temperatures experienced between the outer surface of the beans and and inner core.”

A quick test we use to determine whether beans are raw is to see whether we can easily crush them between our fingers. Roasting makes coffee beans become less dense by making them microporous (Schenker et al,

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