When open-field produce such as lettuce or spinach is harvested, it usually has soil particles such as sand and clay attached to it. For the vegetable processor, it is important to remove these thoroughly. After all, consumers want a clean product. Coarser sand grinds between the teeth and immediately leads to a negative assessment of the product. Finer particles give a rough feeling on the tongue and negatively affect the "mouthfeel."
We distinguish four categories of soil particles by grain size:
Clay < 2 µm
Silt > 2 µm and < 60 µm
Sand > 60 µm and < 2 mm
Gravel > 2 mm
tengsheng conducted both theoretical and experimental research in its own laboratory on soil particles with a focus on how they can be removed and separated from the product. To assess the settling speed in water, grain size and a gentle flow are important. The latter is optimally achieved in a washing or transport flume. In food processing, a flume is a water-filled channel used to transport, wash, or cool fresh produce like vegetables and fruits. It gently moves products through different processing stages while helping to remove dirt and debris. A flume uses laminar flow where the fluid travels smoothly and steadily, with minimal mixing or turbulence.
Due to the long retention time and the laminar flow in the flume, the particles have time to loosen and settle. They are then removed via a so-called “sand trap.” In the case of very large amounts of sand, such as with products like lamb's lettuce, a pre-installed sand remover offers a solution.
Intensive research provided insight into how many particles of a certain diameter are removed in a flume of a certain length. The results of this research are used to optimize tengsheng's washers and processing lines.