Barbecues also have a role in the demand for barrels.
Thieves have some brewers over a barrel as kegs become a valuable commodity amid fizzing prices for scrap metal.
DB said its customers paid a $35 deposit for kegs, which was refunded when the keg was returned.
The 35-litre or 50-litre barrels were coded for identification.
"You can't just bring a keg in and get $35. If you lose the keg it won't be credited to your account."
But the stainless-steel kegs may fetch three times that much on the black market.
An Auckland brewer said the rising price of steel had combined with a Kiwi "tradition" of stealing kegs to create problems for the industry.
"It's a battle," he said, and implored scrap metal dealers to stop buying kegs.
He said some thefts were clearly organised.
Other thefts were impulsive, spontaneous grabs as a result of hoteliers leaving kegs lying around. "A lot of them are turned into hangi and barbecues. Every Kiwi's birthright is to steal a keg and turn it into a barbecue."
Scrap & Demolition magazine said the beer industry lost "huge quantities of kegs every year".
CMA Recycling Tauranga manager Kirk Edwards said most scrap dealers refused to accept stolen goods but a small number of dealers were willing to turn a blind eye.
Edwards said he never bought kegs from the public. "The beer kegs belong to the brewers."
He said New Zealand could follow a British law banning scrap dealers from buying brewery equipment but enforcing the law would be difficult.
Edwards said rising stainless-steel prices, beyond New Zealand's control, generally drove the thefts.
Scrap metal thieves were the bane of railway companies and Housing New Zealand, stealing whatever they could sell as scrap.
"You hear every excuse from 'I've got to feed the kids' to a drug habit."
A 57-year-old Otara man was charged this week with stealing $10,000 of gas cylinders.
The Fire Service has in the past warned people not to handle stolen cylinders because they could blow people's heads off.