I have speculated in this very column whether it is correlated with a liking for cats or dogs.
I have asked what Chinese teas/infusions I would recommend for a coffee lover to try; wheat tea (大麦茶) or burdock-root (牛蒡茶) tea. I have also asked aloud what makes me (and most other people) enjoy one so passionately more than the other.
Well, this month, we have (perhaps) learnt a bit more.
A study by Northwestern University, Illinois, USA, has identified specific DNA differences correlating with humans drinking coffee or tea.
This study focuses on taste genes, finding that some people are more able than others to recognise the taste of caffeine.
A higher recognition of the caffeine taste was correlated with a higher preference for drinking coffee. It had previously been assumed that humans instinctively dislike foods and drinks tasting bitter to them, “reading” them as poison. Those more sensitive to bitterness, it was assumed, would avoid those bitter things.
But in this research, the bitterness-aversion idea was reversed. Why? The researchers concluded that coffee drinkers associate the bitter flavour of caffeine in coffee with the psycho-stimulant effects (the buzz) from caffeine. Tea, in this study, initially appears to be just a fallback or default; it is “what people probably drink if they don’t crave that caffeine bitterness tasted in coffee”.
Tea is just assumed to contain less caffeine or “taste less” of caffeine. So far, so reductive.
But, actually, the “caffeine taste” was not the only strong bitterness these researchers observed; they also looked at perceptions of quinine (the mild-poison that gives tonic water its distinct, bitter taste). And they looked at perception of PTC, geneticists’ favourite “bitter” compound, which can be found in broccoli, cauliflower, kale, Brussels sprouts and cabbage, but not all green vegetables.
If you can tolerate these forms of bitterness, the study suggests, you are more likely to favour tea over coffee. One problem with these findings is that they are pieced together from separate studies, from different regions of the world (the UK, USA and Australia). There is a lot of guesswork involved in linking these different bitterness perceptions.
But, even if this research does not amount to a bag of beans, it is likely that genetic influences will be flagged more effectively in the future.
“Taste genes” have mostly been identified with bitterness so far, but that picture will surely broaden. Tannic compounds, such as theanine and EGCG (ignored in this study) are a particularly important aspect of the taste profile of tea.
And taste alone may not entirely account for the “nature” aspect of drink preferences. Surely there is genetic variation in the way different humans metabolise (and perceive) caffeine.
Of course, there is also the “nurture” aspect. My parents, for example, were turned off tea through associating it with stale, stuffy ancestors. For China’s Starbucks generation, there is perhaps a similar phenomenon in play (though a liking for pumpkin spice latte arguably has little to do with a liking for coffee). Yet, science will struggle to round up such influences, since we do love to read about definitive “root causes”.
So expect to see research soon establishing a genetic predisposition for black tea-drinkers pouring milk before or after* boiling water.
*both, incidentally, are vulgar.