ABInBev is investigating what went wrong at its Magor brewery in Wales, after Budweiser bottles filled at the site were found to contain large glass fragments last week.

The problem was detected by two separate consumers, who reported their findings to the brewer, which immediately issued a recall on 15 November. Neither person suffered injury. Both bottles were produced on the same line and were part of the same 15x300ml batch, produced at Magor on 14 September.

"We have identified a possible mechanical cause related to a bottle filler," said a spokeswoman for ABInBev. The recall affected nearly 300,000 bottles, but ABInBev produces more than one billion bottles of beer every year in the UK, so any impact on its star-performing beer would be "quite limited", she added.

Sales of Budweiser are up 54.1% to £240.1m [Nielsen MAT 2 October 2010].

Earlier this month Carlsberg UK recalled some 275ml bottles of Tuborg lager sold in bottle packs, saying they might contain small pieces of glass.

And a beer buyer for the big four speculated that, with the increasing use of lightweight bottles, this may not be a conincidence. "It is interesting to note" that two major brewers have declared similar recalls on batches of bottled beer within a short space of time, he said.

"We're seeing quite a few suppliers moving to thinner glass to reduce the weight, get cost efficiencies into the product and reduce transportation costs. The problem is if you get too thin it can result in shattering down the production line."

However, the ABInBev spokeswoman said this recall had "nothing to do with lightweighting of ­bottles".

The affected packs of Budweiser have a 'Born on' date of 14 September and a site reference of 107A or 107 on the bottle, and should be returned to retailers.