THINK of the creaminess of mayonnaise, the viscosity of toffee and the greasiness of cold lard. Or the brittleness of butterscotch, the elasticity of jelly and the crunchiness of fresh carrots. Careful not to dribble. You have entered the complex world of mouth feel.
Mouth feel is the technical term food scientists use to describe how food feels in your mouth. You may think you know how, say, a piece of chocolate feels when you are munching it. But food scientists want to know about all the physical and chemical interactions going on in your mouth. Try putting precisely what you’re experiencing into words and you’ll begin to see why mouth feel is so hard to define.
What’s the technique? Start with the first sensation you get when you put the food in your mouth – is it rough, smooth, oily or wet? Then consider how the food responds to your first bite – how much of it deforms instead of fracturing, for example. After a few chews, think about how much moisture the sample has released and how its density changes as it mixes with your saliva. Then get a sense of how greasy or creamy it feels and how well it sticks to your molars. Finally, reflect on the act of swallowing: how much is left in your mouth, how tacky your tongue feels against the roof of your mouth and the degree of “tooth packing” – how much of the stuff gets stuck in your teeth.
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“Get a sense of how creamy it feels, how it sticks to your molars”
Trickier than you imagined? You’d have thought by now someone would have invented a machine to measure mouth feel. They haven’t quite, though not for lack of trying. In the early 1960s Alina Szczesniak, a food scientist at the US food giant General Foods, developed a way of correlating machine readings with sensory ratings. She classified food textures into three categories: mechanical properties such as hardness and elasticity, geometric properties such as the size, shape and orientation of food particles, and other properties such as moisture content and oiliness.
Trained food tasters can be surprisingly accurate and consistent when it comes to rating such properties on scales of, say, 1 to 10. Szczesniak correlated these subjective sensory ratings with objective measurements of the way food samples flow and deform when a force is applied, a branch of physics known as rheology. Today, no self-respecting food laboratory is properly equipped without both a human tasting panel and an armoury of machines for making texture measurements.
Japanese researchers have gone one step further. They have built a food simulator that can create different textures in the mouth. It consists of a device that resists the chewer’s bite, a system of tubes that squirt flavours onto the tongue and a microphone that plays the sound of a chewing jawbone into the user’s ear – the basis of a new diet plan, perhaps?