A method to assess the ability of rough surfaces to eliminate slip in food viscosimetry

In squeezing flow viscometry the presence or absence of friction between the specimen and the plates has a dramatic effect on the flow curve characteristics. It is therefore proposed that the method can be used to test whether a given surface, with a particular rough finish, is effective to eliminate slip of a given self-lubricating food. The concept is demonstrated with experimental data of commercial samples of mayonnaise and mustard, which were pressed between pairs of parallel polished and rough metal plates in an imperfect squeezing flow array, and their force height relationship was recorded. In all the cases, the absolute magnitude of slope of the log-force versus log height plot was smaller than one. This shows that these two products are self-lubricating to such an extent that roughening of the plates surface, at least to the extent used in this work, can be an ineffective means to avoid slip. Similar results have been previously reported in three different kinds of tomato products, which suggests that the problem may not be limited to food emulsions