Electronic nose knows quality coffee

Bryn Nelson Columnist

Ah! A bold espresso that boasts intense flowery, winey, citrus, acid — and yes, even butter toffee notes. So says an electronic nose, anyway.

Behold, the coffee snob of the future.

Perhaps the machine assembled by scientists at the Nestlé Research Center in Switzerland isn’t quite ready to be called into daily demitasse-sipping service. But in an analytical test of its abilities, it predicted the range of aromas and intensities noted by a panel of experts for 11 different espressos, with few mismatches. And in a subsequent validation, the electronic nose nearly duplicated the panel’s opinion in characterizing an additional eight espressos.

In the quest for consistently high-quality java, the coffee industry stands to benefit enormously from any nose that really knows its stuff, whether attached to a person or a machine.

“We do not attempt to replace human tasters by instruments but to assist human tasters,” said Nestlé researcher and lead author Christian Lindinger, whose report was published last month in the journal Analytical Chemistry. “But in some cases we can use the approach as a pre-screening tool to eliminate those samples which would anyhow fail a sensory evaluation because of insufficient quality.”

The perfect espresso
Researchers already have developed prototype electronic noses to analyze perfumes and wines as well as to monitor landfill odors, distinguish between smoke from fires or cigarettes, warn of hazardous gases or narcotics and even detect the warning signs of pneumonia and asthma in a person’s breath.

With more than 1,000 organic compounds contributing to a roasted coffee’s aroma, sniffing out the perfect espresso has lagged behind a bit. Recent research, however, has suggested that only 50 of those chemicals might be necessary for mapping out the sensory profile of that aroma — and perhaps even less for accurately reproducing it.

For their study, the researchers used a standard espresso machine (made in Switzerland, of course) to prepare the different samples. The team poured each one into a setup that allowed the espresso’s heated gases to waft up from an oven to a chemical detector known as a proton-transfer reaction mass spectrometer. The mass spectrometer recorded the prevailing gas mixture and a mathematical model then translated the most useful chemical information into a more understandable description.

Lindinger said the model can predict the sensory profile of an unknown espresso based solely on the chemical measurements. It’s also possible, he said, to discern the mix that correlates with a specific attribute like, say, flowery notes, provided that the right balance of compounds is carefully recorded.

With their human noses to guide them, an in-house panel of 10 experts from across Europe also evaluated each espresso on its range of attributes, scoring each as weak, medium or high-intensity. One espresso was noted for its strong “butter toffee” quality, while another scored best on its “woody” attribute and a third was, alas, deemed particularly “bitter.”

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