How do you investigate and solve commercial yield problems?
Written by MM
This section of the Dairy Science and Food Technology website provides an outline of how the commercial 'cheese yield problem' outlined earlier might be approached and how yield and cheese component retention can be analysed and presented. This is achieved using a unique on-line calculator that is shown in the cheese yield spreadsheet.
Data from 5 vats of commercial Cheddar production are summarised in the cheese yield spreadsheet. The data set are different to the problem given previously. The cheese and milk data were obtained from one day's production. The casein:fat ratio of milk in each vat has been calculated and for information casein as a percentage of protein has been presented.
If you want to analyse your own data simply replace the data in the editable cells in the calculator below and press the submit button. The calculator will then give basic statistical information along with the results of the theoretical yield and cheese component-retention calculations.
Actual yield data have been presented and for comparison, theoretical yield has been predicted using the Van Slyke yield equation. There is a less well known variant of the Van Slyke equation that does not require cheese moisture but does assume a target moisture content. This is arguably more useful in cheese plants and has been included to enable predicted values to be compared with actual and traditional Van Slyke yields.
Some basic statistics, mean, standard deviation and coefficient of variation have been presented.
Readers can also input their own data and use this basic data analysis and presentation package to analyse and present their data.
Main findings from the data presented
Firstly the data set is very small! Meaningful commercial analysis would require a much larger sample size. However, the use of mean values combined with the standard deviation and the coefficient of variation can provide some basic insights into errors.
Note the differences in CV between the protein, fat and casein values in milk and the values for cheese. While the CV values for casein and fat in the cheese milk probably reflect what might be achieved in many factories it would be helpful to have lower values particularly when working with small numbers of samples.
The casein:fat ratio is less than optimal. Protein and consequently casein levels are low and would be expected to give 'low' but predictably low cheese yields.
Cheese moisture values are on the low side. There is an indication, but the sample size is very small, that there is some variation in moisture values between vats.
Cheese yields are low due to the low casein levels in the milk and low moistures in the cheese. Adjustment of yields to 37% moistures shows the increase in yield that would be possible if the casein:fat ratio and cheese making operations were optimal. This again must be qualified by the small sample size.
With this data set the Van Slyke equation underestimates and the modified equation over estimates yield. The sample size is too small to make more definitive comments except to say that actual yield is broadly in line with theoretical yield.
This view is partly strengthened by looking at the mean values for casein, fat and protein retention. Again it is necessary to qualify comments based on the small sample size. Protein retention is a little higher than expected and fat retention is close to the theoretical maximum.
Action that is required
Milk composition must be standardised to obtain optimal casein:fat ratios for Cheddar cheese making.
An improved protocol for sampling cheese milk for protein, fat and casein analysis is required.
Compositional quality of the milk for cheese manufacture should be improved.
Further work on cheese moisture is required. This should also look at salt levels in the cheese and will involve looking closely at the process e.g. process control and the equipment e.g. cheese knives. See the section on mellowing.