Thomas Vilgis, a food physicist at the Max Planck Institute for Polymer Research in Germany, has been in love with Foie Gras for a quarter century. The gorgeous delicateness is a putty or mousse made from the rich, fat liver of ducks and geese.
“It's truly extraordinary,” Dr. Virgis said, recalling his early encounters with high-quality foie gras when he lived and worked in Strasbourg, France. It was soft and buttery, and as the fat started to melt in my mouth, the flavor evolved and exploded. “It's like fireworks. Suddenly there's a feeling of the whole liver,” he said.
But such transcendence is at a price.
To fatten the liver used to create foie gras, farmers force more grains than their bodies need. The excess food is stored as fat in the animal's liver and has balloons of size.
He sometimes eats foie gras produced by local farmers, but Dr. Virgis discovers unbearable power on an industrial scale. “It's terrible to watch,” he says.
Dr. Virgis somehow wondered whether it could be “made a similar product, but without this torture.”
In a paper published Tuesday in the Journal of Liquid Physics, he and his colleagues say they believe they have devised techniques to help ducks and geese eat and grow normally. But to be clear, this is not a replacement for foie gras that will hold the life of birds.
His lab approach uses enzymes to break down duck fat. Second, the mixture of regular duck liver and treated fats is finished in the same way as traditional foie gras. “Of course, that's not a 100% agreement, but we're very close,” Dr. Virgis said.
“It's far better than many other products that try to simulate foie gras,” he said. It involves the process of using plant fats (“the same flavor, not melting, nothing,” he said) or collagen (“this turns out to be gum,” he said).
Devising this approach was full of failure. When the team tried simply to combine regular duck liver with untreated fat, regardless of the ratio, the result was not foie gras.
“The mechanical properties are different,” he said. “The fat distribution is different. Everything wasn't working.”
Researchers tried to add emulsifiers and later gelatin from bird skin and bones, but consistency was off.
Dr. Virgis then thought about what would happen when forces were generated inside the bird's body. Ducks or geese, among other things, digest all the excess food using an enzyme called lipase, which acts like a pair of molecular scissors. They can cut fat molecules into small pieces and “rearrange and crystallize in different shapes,” he said. Crystallized fats form irregular clusters surrounded by a matrix of liver proteins, giving them a luxurious flavour and texture.
That was an important insight. “We just did what happens in the small intestines of the lab,” Dr. Virgis said. When the team treated duck fat with lipase, mixed it with regular liver, and studied it using X-ray scattering and other techniques, the results were markedly similar to foie gras.
“The mechanical properties match the properties of foie gras very well,” he said. “This really made me happy because foie gras contains so much basic physics.”
But most importantly, it tasted right. Dr. Virgis was surprised and pleased when he first sampled the fake foie gras. The team adjusted the melting point and fat clustering exactly to the right. “This trick gives you fat so that it melts in your mouth, which is essential,” he said. Dr. Virgis secured a patent for this process.
Roseanna Zia, a mechanical and chemical engineer at the University of Missouri, praises the research that overcomes important challenges as she was not involved in the study. “One of the difficult things about engineering is to translate what people like and want,” she said.
She explained that foie gras is a kind of soft solid, including butter, chocolate, mayonnaise and ice cream. “It looks like a solid, but when spread out with a knife, it moves like a liquid,” she praises researchers like Dr. Virgis, who can manipulate the behavior of this type of complex material.
He acknowledges that his formulation is “not vegetarian, not vegan.” However, when foie gras is produced and consumed, Dr. Virgis hopes at least some farmers will work to “reduce the suffering of animals a little.”
