Donal O’Callaghan, researcher at the Teagasc Food Research Centre in southern Ireland and one of the authors of the study published in this month’s Journal of Dairy Science, told DairyReporter.com that the findings flag up the importance of milk standardisation in the manufacturer of cheese, regardless of type.
He notes that on per country basis, some cheese making factories adopt milk standardisation, others follow a more tradition based process.
“This is the first study to document experimental data to investigate the effects of milk composition, stir-out time, and pressing duration on curd moisture and yield,” said O’Callaghan in relation to the benefits for industry of the results of the research.
Control of cheese moisture is paramount to maximizing yield and profitability but final moisture is affected by many cheese-processing conditions such as coagulation time, curd particle size, stirring, cooking temperature, and ex-vat curd handling.
The team of scientists, which included researchers from University College Dublin and the University of Kentucky in the US, found that milk total solids, involving fat or casein, has an effect on curd moisture after pressing, which has implications for milk standardization.
They said that their results show a need to standardize on a fat and casein and not just a protein:fat basis.
“Increasing milk fat level at constant total solids was found to decrease curd moisture at draining and after pressing (i.e., moisture in cheese is associated with protein more than with fat),” said the researchers.
However, protein level in milk did not affect curd yield or moisture after pressing, which the authors note “confirms the importance of moisture control at drainage.”
Pilot scale analysis
The researchers explained that for the study, milks of varying protein levels and protein:fat ratios were renneted under normal commercial conditions in a pilot-scale cheese vat.
During the syneresis phase of cheese making, curd was removed at differing times, and curd moisture and yield were monitored over a 22 hour pressing period, they added.
Curd moisture after pressing decreased with longer stir-out time and pressing duration, and an interactive effect was observed of stir-out time and pressing duration on curd moisture and yield.
“A decreased protein:fat ratio was associated with increased total solids in milk and resulted in decreased curd moisture and increased curd yield after pressing.”
The variation in total solids of the milk explains the apparent contradiction between decreased curd moisture and increased curd yield, they added.
The authors conclude that there is as role for process analytic technology in minimizing variation in cheese characteristics through better control of cheese milk composition, in-vat process monitoring (coagulation and syneresis), and post-vat moisture reduction (curd pressing).
Increased control of curd composition at draining would facilitate increased control of the final cheese grade and quality, they added.
Source: Journal of Dairy Science
Published online ahead of print: doi: 10.3168/jds.2010-3575
Title: Effects of milk composition, stir-out time, and pressing duration on curd moisture and yield
Authors: CD Everard, DJ O'Callaghan, MJ Mateo, M Castillo, FA Payne, CO O'Donnell