But why? "The kernel of this idea of pairing astringents with fats is found in gastronomies all over the planet, but it's never been clear how or why these pairings work," said Paul Breslin, an experimental psychologist at Rutgers University and Monell Chemical Senses Center who studies taste perception.
In a new paper published online Oct. 8 in the journal Cell, Breslin and colleagues propose a theory of food pairings that explains for the first time how astringent and fatty foods oppose one another to create a balanced "mouthfeel."
Because fat is oily, eating it lubricates the mouth, making it feel slick or even slimy, Breslin said. Meanwhile, astringents, chemical compounds such as the tannins in wine and green tea, make the mouth feel dry and rough. They do this by chemically binding with lubricant proteins present in saliva, causing the proteins to clump together and solidify, and leaving the surface of the tongue and gums without their usual coating of lubrication. [Tip of the Tongue: The 7 (Other) Flavors Humans May Taste]
We don't like slimy, but we don't like puckered up, either. "We want our mouth to be lubricated but not overly lubricated," Breslin told LiveScience, a sister site to Life's Little Mysteries. "In our study, we show that astringents reduce the lubricants in the mouth during a fatty meal and return balance."
Although this food-pairing idea had been proposed before, it was a mystery how that balance might actually be struck, because wine, green tea and the other widely consumed astringents are only mildly astringent. No one knew how they managed to cut the fat as well as they do. [Will People Really Be Forced to Stop Eating Meat?]
The researchers discovered that astringents have a stronger effect each time the mouth is exposed to them. Every time study participants took a sip of green tea, for example, they perceived it to be more astringent than during the previous sip, indicating that the astringents were reacting more strongly with the lubricating proteins in their mouths upon each exposure. This growth in astringency is why, even though tea and wine have only a weak effect at first, sipping them throughout a fatty meal eventually enables the astringents to counterbalance the strong lubricating effect of the fat.
A second experiment supported this conclusion. When the study participants alternated their sips of tea with bites of salami, the perceived slipperiness of their mouths (caused by the fatty salami) gradually decreased as they took more sips. When they sipped water, by contrast, the slimy feeling in their mouths continued to build.
The importance of repeated exposure explains why we don't tend to gulp down an entire glass of wine then eat our entire steak. Nor do we polish off our whole pickle before setting into our sandwich. The new research justifies the widespread use of astringent foods as "palate cleansers" that people sample throughout a meal.
This general principle of yin and yang food pairings goes part of the way in explaining gastronomy, but what about the specifics? Why do we pair sushi with pickled ginger rather than with a soda, despite the fact that they're both astringents? And why does cheese seem to taste better with red wine than with green tea? As Breslin put it, "Is there something to the idea that a particular astringent and a particular fatty food go together?"
The famous pairings could simply be cultural accidents — a matter of which foods were available in which regions. But Breslin said it's also possible that cultures have unknowingly worked out the most balanced pairings based on the chemical properties of the foods.
"Different kinds of astringents give rise to different rates of growth of astringency. As you repeatedly sample them, one will have a steep rise and the other a shallow rise," he said. "It could be that there's a particular mixing of an astringent and a fatty food that determines how strong the astringent is going to be and how quickly it gets there. This is a mystery of gastronomy."