(CNN) -- A man walks into a supermarket, hands over a beer can and receives money back. This may seem contrary to the natural order -- but it's all part of brewer Carlsberg's sustainability drive.
Central to this is Carlsberg's use of Denmark's reverse vending machines, run by Dansk Retursystem.
There are 3,000 of these futuristic reverse vending machines dotted around Denmark, through which 3 million items are deposited every day. You put a can or bottle into the machine and it gives you a voucher or money back for your efforts.
The number of packages returning through the system is astonishing: 90% of cans designed for single use are recycled, and nearly 100% of refillable bottles find their way back to Carlsberg.
The brewing giant's bottles and cans themselves are designed to be as sustainable as possible.
To make packaging more environmentally friendly, "the most obvious thing we can do is reduce the weight," said Simon Hoffmeyer Boas, CSR manager. Lighter products can lessen energy needed in the manufacturing process, and "within the last 20 years the average weight of a glass bottle has been reduced by approximately 30%," Hoffmeyer Boas said.
The innovation makes the bottles cheaper to manufacture, alongside being better for the environment. "For us sustainability, or CSR, is business, it's not something that is detached," he said.
From the barley to the bottle, every part of the process is scrutinized by the company's research and development department to ensure it meets or beats sustainable targets.
In the Carlsberg laboratory, where the pH scale was developed, new types of barley are developed. In 2010 the company introduced the Null Lox variety.
Brigitte Skadhuge, director of applied research, told CNN that type of barley "helps beer to stay fresh for a longer time than traditional beer." That gives beer a longer shelf life, reducing waste.
The by-product of the spent grain also helps power the plant. The husk, the outer covering of the barley grain, is placed in a bi-fermentor which transforms the cellulose into methane gas. This gas provides 90% of the thermal energy needed at the plant.
Even the waste from the waste is put to good use -- the waste from the bio-fermentor is used as a natural fertiliser in the barley fields.