Bigger the size of wine glasses, even without increasing the amount of wine, leads people to drink more, suggests a new study by the University of Cambridge.
Wine sales in bars and restaurants are either of fixed serving sizes when sold by the glass, or for free‐pouring by customers or by the bottle when sold by the bottle or carafe. Sales by the bottle or carafe are more typical in eateries than bars. The size of wine glasses may influence deals in an unexpected way, contingent upon whether it is sold by the glass or by the bottle or carafe.
For the study, the Cambridge team did a ‘mega-analysis’ that brought together all of their previously published datasets from studies carried out between 2015 and 2018 at bars and restaurants in Cambridge. The team used 300ml glasses as the reference level against which to compare differences in consumption.
In restaurants, when glass size was increased to 370ml, wine sales increased by 7.3%. Reducing the glass size to 250ml led to a drop of 9.6%, although confidence intervals (the range of values within which the researchers can be reasonably certain their true value lies) make this figure uncertain. Curiously, increasing the glass size further to 450ml made no difference compared to using 300ml glasses.
First author Dr. Mark Pilling said, “Pouring wine from a bottle or a carafe, as happens for most wine sold in restaurants, allows people to pour more than a standard serving size, and this effect may increase with the size of the glass and the bottle. If these larger portions are still perceived to be ‘a glass,’ then we would expect people to buy and consume more wine with larger glasses.”
“As glass sizes of 300ml and 350ml are commonly used in restaurants and bars, drinkers may not have noticed the difference and still assumed they were pouring a standard serving. When smaller glass sizes of 250ml are available, they may also appear similar to 300ml glasses but result in a smaller amount of wine being poured. In contrast, huge glasses, such as the 450ml glasses, are more obviously larger, so drinkers may have taken conscious measures to reduce how much they drink, such as drinking more slowly or pouring with greater caution.”
Senior author Professor Dame Theresa Marteau said, “If we are serious about tackling the negative effects of drinking alcohol, then we will need to understand the factors that influence how much we consume. Given our findings, regulating wine glass size is one option that might be considered for inclusion in local licensing regulations for reducing drinking outside the home.”
Professor Ashley Adamson, Director of the NIHR School of Public Health Research, said: “We all like to think we’re immune to subtle influences on our behavior – like the size of a wine glass – but research like this clearly shows we’re not.“
“This important work helps us understand how the small, everyday details of our lives affect our behaviors and so our health. Evidence like this can shape policies that would make it easier for everyone to be a bit healthier without even having to think about it.”
Clive Henn, a Senior Alcohol Advisor at Public Health England, welcomed the report: “This interesting study suggests a new alcohol policy approach by looking at how the size of wine glasses may influence how much we drink. It shows how our drinking environment can impact on the way we drink and help us to understand how to develop a drinking environment, which helps us to drink less.”
The study received additional funding from Wellcome.