M.J. Mateo

Effects of cutting intensity and stirring speed on syneresis and curd losses during cheese manufacture.

Recombined whole milk was renneted under constant conditions of pH, temperature, and added calcium, and the gel was cut at a constant firmness. The effects of cutting and stirring on syneresis and curd losses to whey were investigated during cheese making using a factorial design with 3 cutting modes designed to provide 3 different cutting intensity levels (i.e., total cutting revolutions), 3 levels of stirring speed, and 3 replications. These cutting intensities and stirring speeds were selected to give a wide range of curd grain sizes and curd shattering, respectively. Both factors affected curd losses, and correct selection of these factors is important in the cheesemaking industry. Decreased cutting intensity and increased stirring speed significantly increased the losses of fines and fat from the curd to the whey. Cutting intensities and stirring speeds in this study did not show significant effects on curd moisture content over the course of syneresis. Levels of total solids, fines, and fat in whey were shown to change significantly during syneresis. It is believed that larger curd particles resulting from low cutting intensities coupled with faster stirring speeds resulted in a higher degree of curd shattering during stirring, which caused significant curd losses.

Validation of a curd-syneresis sensor over a range of milk composition and process parameters

An online visible-near-infrared sensor was used to monitor the course of syneresis during cheesemaking with the purpose of validating syneresis indices obtained using partial least squares, with cross-validation across a range of milk fat levels, gel firmness levels at cutting, curd cutting programs, stirring speeds, milk protein levels, and fat:protein ratio levels. Three series of trials were carried out in an 11-L cheese vat using recombined whole milk. Three factorial experimental designs were used, consisting of 1) 3 curd stirring speeds and 3 cutting programs; 2) 3 milk fat levels and 3 gel firmness levels at cutting; and 3) 2 milk protein levels and 3 fat:protein ratio levels, respectively. Milk was clotted under constant conditions in all experiments and the gel was cut according to the respective experimental design. Prediction models for production of whey and whey fat losses were developed in 2 of the experiments and validated in the other experiment. The best models gave standard error of prediction values of 6.6 g/100 g for yield of whey and 0.05 g/100 g for fat in whey, as compared with 4.4 and 0.013 g/100 g, respectively, for the calibration data sets. Robust models developed for predicting yield of whey and whey fat losses using a validation method have potential application in the cheese industry.

Effects of milk composition, stir-out time, and pressing duration on curd moisture and yield

A study was undertaken to investigate the effects of milk composition (i.e., protein level and protein:fat ratio), stir-out time, and pressing duration on curd moisture and yield. 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-h pressing period. 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. Milk total solids were shown to affect curd moisture after pressing, which has implications for milk standardization; that is, it indicates a need to standardize on a milk solids basis as well as on a protein:fat basis. In this study, 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. This study points to a role for process analytic technology in minimizing variation in cheese characteristics through better control of cheesemilk 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.

Comparison between red-green-blue imaging and visible-near infrared reflectance as potential process analytical tools for monitoring syneresis.

The current work focuses on the comparison of 2 on-line optical sensing systems; namely red-green-blue imaging and visible-near infrared reflectance, for monitoring syneresis during cheese manufacture. The experimental design consisted of 3 temperature treatments carried out in an 11-L cheese vat in triplicate. Both systems were shown to predict syneresis without significant differences in prediction accuracy. However, a single-wavelength near infrared model was the most parsimonious (standard error of prediction=4.35g/100g) for predicting syneresis. This technique was also the simplest in terms of parameters in the model (standard error of prediction=4.15g/100g with 2 parameters), when time after gel cutting and process parameters (temperature and cutting time) were included in the models. The study showed that either system could be employed to control syneresis in cheese manufacture and improve the control of moisture content in cheese.

Using Light Backscatter at 980 nm to Determine Curd Moisture Content at Various Milk Fat and Gel Firmness Levels in Cheese-making

Curd moisture control plays a fundamental role in determining the quality of the final cheese. A large field of view (LFV) light backscatter sensor at 980 nm was used as a rapid on-line method for monitoring curd moisture content changes during syneresis. Improving the control of curd moisture content during the cheese-making process may enhance product consistency and reduce the overall production cost. The objective of this study was to evaluate the influence of two experimental variables (i.e. fat and gel firmness at cutting) using light backscatter at 980 nm on syneresis and curd moisture content prediction. An experiment was conducted in which whole milk was recombined at three fat levels, clotted under constant conditions and the milk gel was cut at three gel firmness levels. The curd-whey mixture was stirred in the vat after gel cutting and the syneresis process was monitored using the LFV sensor which was installed in the cheese vat wall.

Chapter 6 – The Syneresis of Rennet-Coagulated Curd

Gels formed from milk by renneting or acidification under quiescent conditions may subsequently show syneresis, that is, expel liquid (whey), because the gel (curd) contracts. Under quiescent conditions, a rennet-induced milk gel may lose two-thirds of its volume, and up to 90%, or even more, if external pressure is applied. Often, syneresis is undesired, for example, during storage of products like yogurt, sour cream, cream cheese, or quark; hence, it is useful to know under what conditions syneresis can be (largely) prevented. In making cheese from renneted or acidified milk, syneresis is an essential step. Consequently, it is useful to understand and quantitatively describe syneresis as a function of milk properties and process conditions, particularly when new methods or process steps are introduced in cheesemaking.

A Novel Sensor to Monitor Colour Changes during Cheese Curd Syneresis in a Vat

Syneresis is a critical processing step in cheese manufacture, follows the cutting of milk coagulum into cubes and is promoted by stirring. During the syneresis phase shrinkage of the casein micelle network induces whey expulsion from the curd grains. The rate and extent of syneresis plays a fundamental role in determining the moisture, mineral and lactose content and texture of drained curd and hence that of the final cheese.