The size of glass used for serving wine can influence the amount of wine drunk, say, researchers, adding that when restaurants served wine in 370ml rather than 300ml glasses they sold more wine, and tended to sell less when they used 250ml glasses. The preliminary study, published in the journal Addiction, suggested that serving wine in larger wine glasses -- while keeping the same measure -- led to a significant increase in the amount of wine sold.
"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," said study first author Mark Pilling from University of Cambridge in the UK.
"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," Pilling added.
To provide a robust estimate of the effect of the wine glass size on sales -- a proxy for consumption -- the research 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 the differences in consumption. In restaurants, when glass size was increased to 370ml, wine sales increased by 7.3 percent, the study said.
Reducing the glass size to 250ml led to a drop of 9.6 per cent, although confidence intervals (the range of values within which the researchers can be fairly 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, the researchers said.
"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," Pilling said.
"In contrast, very large 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," Pilling added.
The researchers also found similar internal patterns to those reported in previous studies, namely lower sales of wine on warmer days and much higher sales on Fridays and Saturdays than on Mondays.
The researchers found no significant differences in wine sales by glass size in bars -- in contrast to the team's earlier study.
This shows the importance of replicating research to increase our ability to detect the effects of wine glass size.
According to the study, when combined with data from other experiments, the apparent effect in bars disappeared.
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