Yield loss of cottage cheese curd due to the formation of minor sludge: the beneficial effect of homogenization

The formation of sludge on the bottom of vats during cottage cheese manufacture was investigated. The sludge layer contained 4.23-8.11% of the casein originally present in the vat and was probably caused by agglutinins present in the skimmed milk. Homogenization of the skimmed milk before addition of starter reduced the agglutination of bacteria during the early stages of acid development and eliminated minor sludge formation. Curd yield was increased by up to 5% and average manufacturing time was reduced by 40 min following homogenization.     

UHT processing of milk: seasonal variation in deposit formation in heat exchangers

Deposits formed in different sections of a pilot-scale plant during ultra-high temperature (UHT) processing of milk were studied over a 12-month period. A twofold range in efficient process run time was found. Deposits formed in the lower temperature (80–110°C) section at a constant rate, irrespective of milk composition. The run time was determined almost entirely by deposits formed in the steam-heated section (110–140°C) and these varied greatly in composition and rate of formation throughout the year. To increase run time in commercial practice it is suggested that attempts should be made to reduce mineral deposition in the high temperature section of the plant.     

Manipulation of Dhaka cheese curd and effects on cheese quality

Dhaka cheese is a semihard artisanal variety originating from Bangladesh where manual curd kneading is a normal stage in its manufacture. Dhaka cheeses were produced with different degrees of curd kneading to quantify the curd manipulation process in terms of pressure and to standardise the length of operation. The effect of manipulation on the composition, rheology, texture and microstructure of fresh cheese was also studied. Manipulation had significant effects (P < 0.05–0.001) on most of the parameters studied. One minute of curd manipulation was found to be sufficient for Dhaka cheesemaking.     

Pressing technique and its effect on the quality of Dhaka cheese

Dhaka cheese is a semihard artisanal variety made mainly from bovine milk, using very simple pressing methods. Experimental cheeses were pressed at gauge pressures up to 31 kPa for 12 h at 24 °C and 70% RH. These cheeses were subsequently examined for their compositional, textural and rheological properties plus their microstructures investigated by confocal laser microscopy. The cheese pressed at 15.6 kPa was found to have the best compositional and structural properties.     

Measurement of ionic calcium in milk

There are many reports in the literature regarding the effects of ionic calcium on reactions related to casein micelle stability, such as heat stability, ethanol stability and susceptibility to gelation, sediment formation and fouling. However, experimental evidence supporting these assertions is much less readily available.
This paper evaluates three selective ion electrode systems for measuring ionic calcium directly in milk as well as looking at the effects on pH reduction and addition of calcium chloride.
The best electrode system was the Ciba Corning 634 system, which was designed for blood but has been modified for milk. This was found to be reproducible and stable when calibrated daily and allowed direct measurements to be taken on milk in 70 s. This has been found to perform well now for 3 years. The other systems were not so useful, as they took longer to stabilize, but may be useful for higher ionic calcium concentrations, which are found in acidified milk products.
Reducing the pH increased ionic calcium and reduced ethanol stability. Calcium chloride addition reduced pH, increased ionic calcium and reduced the ethanol stability. Readjusting the pH to its value before calcium addition reduced the ionic calcium, but not back to its original value. Milks from individual cows showed wide variations in their ionic calcium concentrations.
This establishes the methodology for a more detailed investigation on measurement of ionic calcium in milks from individual cows and from bulk milks, to allow a better understanding of its role in casein micelle stability.     

Echelon stock formulation for multi-stage lot-sizing with component lead times

Material requirements planning of batch production in multi-stage manufacturing systems is discussed where component parts may have significant non-zero production or purchasing lead time. The presence of such lead time poses a synchronization problem for the rolling horizon planning of component part production in the system. The synchronization problem is analysed, discussed and modelled first for the case of assembly product structures where a component has a unique successor component. The analysis is then extended to the more complex case of general product structures where a component may have multiple successor components. The associated general structure multi-stage lot-sizing problem is then formulated as a mixed integer linear program first in terms of conventional stock, and then reformulated in terms of echelon stock. The echelon stock quantity of a component is its lead-time adjusted total system stock, counted both as a stand-alone component and as part of successor components. The echelon stock formulation permits the derivation of valid inequalities that can be used in an optimal solution method, and facilitates the development of a fast heuristic method for the capacitated problem