Beans, peas and lentils are usually thought of as soft foods. But researchers in Switzerland found that a surprisingly simple change in how they are frozen can give them a much firmer, layered texture.
In a study published in npj Science of Food, researchers at ETH Zurich tested a technique called directional freezing on chickpeas, lentils, peas, soybeans and several types of beans. Instead of separating the legumes into protein, starch and other components, they worked with the whole food. The research group receives financial support from Nestlé, Bühler and Givaudan through the ETH Zurich Foundation. The funders had no role in the study design, data collection, analysis, interpretation or writing, according to the paper.
The process starts simply enough. Researchers soaked the legumes, blended them with water and heated the mixture until it thickened into a gel.
Then they froze it in a way that encouraged ice crystals to grow in one direction.
As those crystals formed, they pushed the solid parts of the legume mixture into parallel layers. When the food thawed, the ice melted away, but the layered structure stayed behind.
The difference is easy to see in the study images. Conventionally frozen chickpea gel looked more uneven inside, while the directionally frozen version developed clear layers running in the same direction.
Those layers also changed the texture.
Directionally frozen chickpea gels were generally firmer and held together better than refrigerated or conventionally frozen versions. The researchers could also make the texture softer or firmer by changing how much chickpea was in the mixture.
At lower concentrations, the gels had a chewiness similar to silken tofu. At higher concentrations, some came closer to mozzarella in laboratory tests, although they were still much softer than firm tofu.
Those comparisons are useful for understanding texture, but they do not mean the foods tasted like tofu or cheese. The study did not test flavor or ask people which versions they preferred.
The technique also worked with many other legumes.
Researchers created layered gels from red, black and yellow lentils, green peas, mung beans, soybeans, black-eyed peas, kidney beans, navy beans, black beans and lupins. Together, the legumes they tested represent about 96% of global legume production.
Not every legume behaved the same way. Red and black lentils and mung beans formed firmer, more stable gels, while black beans were somewhat softer. Soybeans were harder to structure at lower concentrations but became firmer when the researchers used more soybean material.
That variety could eventually be useful. Different legumes, or combinations of them, might make it possible to create foods with a range of textures without relying on isolated proteins or added texturizers.
That is one of the main reasons the researchers are interested in the method.
Many plant-based foods are made by separating crops into ingredients such as protein concentrates and starches, then combining those ingredients again to create a particular texture. This approach keeps more of the original legume together.
But that does not automatically make the final product healthier.
The researchers did not compare vitamin or mineral levels, measure long-term health effects or test whether the nutrients were easier for the body to absorb. They specifically note that future research should look at questions such as protein digestibility and nutrient availability.
It is also worth putting the term “minimal processing” in context.
The chickpeas in the experiment were soaked for 24 hours, blended, heated at 90 degrees Celsius for 30 minutes, frozen for 24 hours and then thawed.
So this is not simply a matter of cooking beans and putting them in the freezer. What makes the method relatively simple is that it avoids the extra step of separating the food into purified ingredients before rebuilding it.
The researchers also say the technique may be possible in a home kitchen. Their most controlled experiments used insulated molds and specialized freezing equipment, but they reported creating similar layered structures with a simple insulated setup in a regular household freezer. The paper also includes a home preparation guide in its supplementary materials.
Whether people would actually want to eat these foods is still an open question.
The researchers measured firmness, structure and chewiness, but they did not conduct taste tests or compare the products with commercial meat alternatives.
For now, the study is best thought of as a proof of concept.
It shows that something as ordinary as the direction in which water freezes can dramatically change the texture of familiar foods such as beans, peas and lentils.
The chair of Food Structure Engineering at ETH Zurich receives financial support from Nestlé, Bühler and Givaudan through the ETH Zurich Foundation. Open-access publication costs were funded by ETH Zurich.