Barbeque warriors may already be somewhat familiar with whiskey salmon, but not quite like this. A group of scientists at Heriot-Watt University in Scotland have discovered a way to convert leftovers from local distilleries into fish food for nearby salmon farms. If the process catches on, it could inject a big boost of sustainability into both the Scotch and salmon industries.

Heriot-Watt University has ties to the whisky industry going back to the 19th century, and its scientists have worked for years to help distilleries find new ways to use their existing resources (it also hosts the Scotch Whisky Research Instituted on campus). Back in the mid-2000s, engineer Alan Harper and colleagues found a new use for the wood from old whisky barrels. The wood -- which starts out as bourbon barrels before being used to age Scotch -- turned out to be ideal for smoking salmon. The researchers soon realized that there were other ways that the two industries could benefit from each other – made even easier by the fact that their facilities are often neighbors.

“There’s one distillery on one of the islands where you can look out the window and see a salmon farm,” Harper said in a phone interview.

Harper and colleagues began looking at potential uses for one of the primary byproducts of whisky distillation: “pot ale,” also known as burnt ale or spent wash. The pot ale is the liquid leftover in a copper vessel after the whisky is distilled.

“It’s quite a complex mixture,” Harper says. “It contains everything that was in the fermented mass before distillation, except the alcohols and various flavoring compounds.”

The pot ale contains yeast residue, carbohydrates, and minerals – and most importantly, protein.

“By pure happenstance, salmon want a protein mixture that’s virtually identical to proteins that come from the extraction of barley,” Harper says. “And when we started looking at the material, this red light flashed, as it turned out this was almost an ideal food for salmon.”

Currently, much of the protein being fed to farmed salmon comes from imported fish meal and soy products. Converting locally sourced pot ale into salmon food would cut down on transportation costs, not to mention add an environmental boon. And there’s more than enough pot ale to go around.

“If you count all the distilleries in Scotland, there’s enough protein from pot ale to supply maybe half of the protein requirements of Scottish salmon,” says Heriot-Watt scientist Julio Traub.

Pot ale contains proteins from both yeast and barley, but for salmon food, Traub and colleagues are just interested in getting the barley proteins from the mix. Thanks to 500,000 pounds (about $800,000) from the Scottish Funding Council and cooperation from the whisky industry, they’ve found a way to get the right nutrients out of the pot ale. They’re keeping their (patent pending) method secret for now. According to Traub, it involves binding proteins to a matrix, and controlling which ones get released. (And remember, there's no alcohol in pot ale, so there aren't going to be a lot of soused salmon bumping around in Scottish fish farms.)

“Currently, the technology used to recover [whisky] byproducts relies on high energy methods,” Traub says. “They use evaporators that use huge amounts of energy. Our method is totally different -- that’s the key innovation of our process, and what’s going to save lots of greenhouse gases.”

The team is already in talks with some of Scotland’s leading aquaculture feed suppliers, and salmon farmers have already started expressing interest in their work. If the pilot tests go well and commercial production proceeds, both the distilleries and the salmon farms could benefit.

“We’re adding value to two very important Scottish industries,” Traub says.

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