“Suddenly, the contents of the coffee can started shrinking. The can was the same size, but there was now 13oz of coffee,” Dworsky goes on. Some years ago, when he called a coffee manufacturer during a bout of downsizing and asked what was going on, he got an amazingly whimsical answer: “'We've fluffed up the beans to expose more sides of each little granule. And it just doesn't fit in the can anymore! We had to put less in.'” He found this less than convincing.

Dworsky has in fact heard a similar argument concerning toilet paper – rolls got shorter because the paper was supposedly now “so fluffy” that it couldn't fit in people's toiler paper holders without a reduction in length, Dworsky says one manufacturer told him.

Consumer watchdog Which? found in 2016 that some brands of toilet paper have lost up to 14% of the number of sheets per roll over two years, without any corresponding drop in price.

Products where fluff could not possibly enter the picture are shrinking too: Some toothpastes have started being sold in tubes that hold less and consequently cost more per millilitre. A study of US breakfast cereals over a three-year period by researchers at Arizona State University and Cornell University in New York found 15 products suffered a reduction in packet size, and in the majority this resulted in an increase in the relative cost for each ounce (28g) of cereal.

Research by the BBC earlier in 2018 also revealed that many popular chocolate bars have reduced in size over the past four years. A Twix, for example, has lost 13.8% of its weight since 2014, while Kit Kat Chunky bars are 16.7% lighter.

Folklore suggests downsizing began in the era of nickel-chocolate vending machines, Dworsky says. In the misty past, about a hundred years ago, some chocolate vending machines took only five-cent coins. When the cost of making the chocolate went up, the story goes, the vendor couldn't just raise the price without building new machines. Instead, they asked for the bars to be made slightly smaller.

Dworsky points out that there isn't any evidence of these specific events, but this it is a good example of the kind of situation that can lead to downsizing today. When costs rise, a company has three options: raise the price; make smaller packages; change the ingredients.

Changing the recipe is a risky business. Not only is there the problem of a product that doesn't taste right – as Chandon, the INSEAD marketing professor, puts it, the three most important things in food are taste, taste, and taste – but secretly substituting sub-par or artificial ingredients can result in a much more serious backlash against a company than even downsizing. “From the late 1970s to the late 1990s, there was some egregious reformulation going on,” says Mark Lang, a professor of marketing at University of Tampa, Florida, who spent many years as a grocery executive.