THE great dwindling-contents dodge is hitting grocery shoppers with "trick" price rises.
The price looks the same, but shrinking weight or volume is disguised by clever packaging.
It was revealed this week that several bread companies had cut the size of their standard loaf by 30g at a time when prices are increasing.
The move has prompted the Australian Consumers Association to relaunch its campaign for a new food labelling system which includes unit pricing.
Food and grocery manufacturers spend millions on finding out how to reduce quantity or lift prices before customers notice and change brands — a process known in the industry as Weber's Law.
Aron O'Cass of the Griffith University school of marketing said this perceptual threshold affected most fast-moving consumer goods with fluctuating in-put costs.
"Changes to ... volume or price are usually only minor enough so the consumer wouldn't notice or be influenced to buy another product," Dr O'Cass said. "Weber's Law is applied when a company is faced with increased product costs and has to either put up prices or reduce product volume to maintain profitability. The most common products affected include chocolate bars, wine, toilet paper, canned foods, biscuits and bread."
Dr O'Cass said wine bottles looked very similar, but volume could vary dramatically bottle to bottle.
Other great beverage favourites are affected. The Australian Bureau of Statistics says the average box of tea bags in 1997 weighed 250g and cost $2.11. By 1999, the price had risen to $3.47 and the weight fallen to 180g.
And the contents of some beer stubbies have dwindled from 375ml to 345ml.
In 1995, the average roll of toilet paper contained 280 sheets. In 1997, this was 270 sheets — and a roll cost about 4 cents more.
The average weight of a can of baked beans has shrunk 20g in the past few years and baby food has diminished by 5g.
Australian Consumers Association spokesman Gail Kennedy said many customers did not realise they were buying less because of clever packaging.
"With tin cans, the bottom ring is larger and the hollow under the can is bigger," Ms Kennedy said. "The cans look the same sitting on the shelves but the volume and cost can vary. The only way to overcome this deception is to introduce unit pricing, which would make it easier for the consumer to compare the value of different-sized and priced foods. Unit pricing is a system where foods are labelled with the price per 100g or l00ml, which would help consumers easily work out how to get the best grocery deal"
The Australian Competition and Consumer Commission has not looked at the effects of product downsizing on consumers.
"If companies are being honest with customers they should alert them that the volume or weight of their product has diminished," Australian Competition and Consumer Commission Queensland regional director Alan Ducret said.
Mr Alan Ducret said the legality of this practice could only be determined by investigating each case.