ETH Zurich Freeze Structuring Textures Whole Legumes

Researchers at ETH Zurich have published a new texturisation method that transforms whole legumes into fibrous, aligned gels. The process, called freeze structuring, requires only water and a freezer, working without protein isolates, additives, or complex extrusion machinery.

Professor Patrick Rühs, head of the Food Structure Engineering research group, explained the goal. "During chewing, a directional, fibrous structure provides a distinctive bite that is familiar to, and enjoyed by, many people," he said. The method aims to replicate the directional arrangement of fibres found in meat and fish.

The Freeze Structuring Process

The technique begins by soaking and finely blending whole legumes into a purée. This purée is heated to 90°C for 30 minutes to gelatinise the starch alongside proteins and cell wall fragments. The resulting gel is then placed in a mould insulated on all sides except one. Freezing from that single, uninsulated side forces ice crystals to grow inward in parallel lines. This action compresses the purée into thin, aligned layers. After thawing to remove the ice, the directional, fibrous structure remains intact.

A Simpler Alternative to Extrusion

This approach presents a stark contrast to high-moisture extrusion, the dominant method for creating plant-based meat textures. Extrusion depends on protein isolates or concentrates, requires substantial capital investment, and needs tightly controlled processing conditions. It also performs poorly with minimally refined inputs like whole legumes.

The ETH Zurich team notes that fractionation processes like those used in tofu production carry a nutritional cost. Their paper states that making tofu removes roughly 85% of dietary fibre, 16% of lipids, and 23% of protein from whole soybeans, which end up in by-products like okara and whey. Freeze structuring works directly on the intact raw material and can be performed using standard freezing equipment already common in food manufacturing.

Texture Results Across Legumes

The research team tested the method on a wide variety of legumes. Doctoral student Andrea Bach, a joint first author on the study, highlighted its broad applicability. "Our method works with legume species that together account for 96 percent of legume production worldwide," Bach said. The firmness of the resulting gel varied significantly depending on the legume used.

The researchers linked the softer results from soybeans and black beans to their higher lipid content and the specific ratio of protein to non-fibre carbohydrate. The solids concentration in the initial purée provided a second way to control texture. Lower-solids samples produced a chewiness similar to silken tofu, while higher-solids formulations could reach several times that level of firmness.

Doctoral student Elin Perler, the other joint first author, pointed to the advantages of this variability. "It’s an advantage to have a range of consistencies," Perler noted. "It allows more flexibility in developing recipes, and it’s even possible to combine different legumes." The research group is now leaving specific recipe development to professional chefs and has begun collaborating with industry partners to explore applications.