Cooling curves for the preliminary design of beef chillers

A multilayer two-dimensional model of beef carcass chilling using CFD-generated heat transfer coefficients was used to calculate the parameters of leg and shoulder cooling curves, assuming an exponential cooling model. A central composite experiment was designed to systematically vary air velocity, side weight and fat thickness. Comparison with experimental data suggests that the predicted characteristic time for the leg, and hence the cooling time to a given temperature, should be multiplied by a correction factor 1.07. The effects of airflow direction and of radiation heat transfer have been quantified. A correlation was proposed to estimate leg centre temperature from shoulder temperature. The shortcut formulae and methods presented here will be useful in the design and troubleshooting of industrial beef chillers. They could also be used in Monte Carlo simulations where a large number of samples are considered, to take into account random variations in product characteristics and operating conditions.     

Controlled atmosphere storage of celery with the silicone membrane system

Laboratory experiments were performed to assess the potential of the silicone membrane system for long term storage of celery under controlled atmosphere (CA) conditions. Designed CO₂ levels of 1.5, 3.5 and 5.5% were selected to calculate the silicone membrane areas to be installed on the chambers. Visual observations, mass losses and physiological analyses were the means selected to assess the quality of the product. Pascal celery, imported from California (USA), was stored at 1.5°C for 29 days under regular atmosphere (RA) with 80% relative humidity (RH), and 128 days under averaged carbon dioxide (CO₂)+oxygen(O₂) concentrations of 0.8+17.7, 2.0+12.6 and 4.0%+9.2% with RH close to saturation. The results showed that the first two CO₂+O₂ combinations were the most suitable CA compositions, among those tested, for long term storage of that cultivar, with total mass losses of less than 30 and 23% respectively. Clean cut celery, grown locally in Québec on organic soil, was stored at 1.5°C under RA with 80% RH and under three CA compositions (1.1+ 14.8, 2.3+7.9 and 3.2% CO₂+5.5% O₂) with RH close to saturation for 62 and 71 days, respectively. The total mass loss averaged 25% and no significant difference was observed between the RA and CA stored celery. In the experiment with Clean cut celery, the losses were mainly attributed to bacterial infections. Both celery cultivars stored under CA with high RH showed better texture and crispness than those stored under RA. It was also noted that the total sugar content significantly increased with storage.     

Refrigeration system optimization

It must first be established that refrigeration is necessary and that the required cooling cannot be achieved more cheaply by other means. The operating costs of a refrigeration system depend mainly on power consumption and this can be reduced by a wide variety of methods. The operating and capital costs should be brought together in the net present value for an appropriate life span. Various case studies are presented. Other relevant factors to be considered in system optimization include control methods, plant siting and the form of contract used.     

Measurement and prediction of freezing times of vacuum canned Pacific shrimp

Freshly cooked Pacific shrimp, vacuum packed in cans fitted with monitoring instruments, were frozen under industrial conditions. Surface heat transfer coefficients were determined experimentally using aluminium cyclinders. Freezing times were measured and also calculated using Plank's equation and the formulae of Cleland and Earle. The investigation indicated that the vacuum level had little effect on the freezing time and that freezing time essentially doubled when cans were enclosed in a commercial carton. For the prediction of freezing times, Cleland and Earle's method was found to be more accurate than Plank's for the tests performed, with predicted values within ± 10% of measured values.