At-line monitoring of milk coagulation for yield optimization

Cheese is obtained from coagulating milk by separating the milk gel into solid curds and liquid whey. The milk gel is cut into small cubes to increase curds surface/volume ratio and allow whey expelling from curds, a phenomenon called syneresis. The objective of any cheesemaker is to optimize the retention of fat and proteins in cheese while the level of moisture is maintained at a controlled level.

The firmness of milk gel when being cut greatly affects Solids Retention Rate, which is the proportion of solids in milk (everything but water) that is recovered in cheese curds. The Solids Retention Rate specifically measures the performance of milk treatment, recipe formulation, coagulation kinetics as well as the relevance of the selected gel firmness at the cutting step. Contrary to the overall cheese yield that is affected by many factors of the process, Solids Retention Rate measures the efficiency of production at the cheese technology level. The Solids Retention Rate may also be called “vat yield” or “coagulation yield”. It represents the efficiency of an industrial process to convert milk into cheese curds and is easily calculated from Milk Solids and Whey solids. Solids that don’t turn into cheese end-up as whey solids losses.

Even though they may be recovered by various processes and turned into whey ingredients, it is in most cases more profitable to retain solids into cheese. For a given milk composition there is an optimal cutting firmness to reach the highest vat yield. Cutting the gel too soft leads to lower vat yield through increased whey fat loss, whereas cutting too firm results in too high curds moisture content and difficult crumbly curds cutting. Suboptimal cutting firmness also alters the ripening process and final product quality.

It is generally known that better profit is made by turning milk solids into cheese compared to reprocessing whey solids to extract fat and proteins. Because whey ingredients have lower value and require extra energy, equipment and staff to be extracted, it is interesting to increase vat yield in order to make more cheese from the same milk volume. In addition, since milk production is responsible for over 90% of cheese making carbon footprint, maximizing vat productivity directly contributes to reducing the environmental impact of the cheese industry.

Presently, in cheese plants, milk gels are cut either: at a fixed time, at a calculated time from measured flocculation time and/or according to cheesemakers’ subjective evaluation of gel texture and appearance. None of these techniques is perfectly accurate nor sensitive enough toward variations of the milk gel firmness. These techniques lead to considerable fluctuations in Solids Retention Rate and combine with many other factors that affect the yield such as seasonal milk variation and complex milk standardizations and treatment.

There is a clear need for objective, quantitative, at-line and real-time measurements of milk gel firmness during coagulation that allow automatic and consistent gel cutting.

This is why Rheolution Inc. developed CoaguSens™ Connect, the first industrial testing instrument that:

—     Quantitatively measures milk gel firmness during coagulation.
—     Monitors close to the coagulation vat the formation of the curd.
—     Automatically triggers cutting when the optimal target firmness is reached by the curd.

This application note presents results obtained in a North-American cheddar cheese plant that deployed the CoaguSens™ Connect to increase Solids Retention Rate.