Interpretive Summary: Effect of hot carcass weight on the rate of temperature decline of pork hams and loins in a blast-chilled commercial abattoir.
By: Dr. Thomas Powell
Carcass chill rate and extent are critical factors in the muscle to meat conversion at slaughter and may very well be the most influential processing determinants of final pork product quality. Chilling rate is greatly influenced by the carcass weight as well as the obvious environmental factors of temperature, air speed and humidity in the cooler. An additional consideration is that different parts of a carcass chill at different rates. For packers, chilling dynamics have been compounded by the historical gradual increase in hot carcass weights. Chilling factors must be balanced to avoid cold-shortening (which occurs when chilling takes place too rapidly) and the other extreme where a carcass chills too slowly resulting in high ultimate pH and pale, soft and exudative (PSE) product.
Blast chilling systems have been implemented in some pork abattoirs to increase air velocity and decrease temperature in the early phase of chilling to improve the chilling of heavier carcasses. The University of Illinois and the USDA Meat Animal Research Center recently published a study in the Journal of Animal Science documenting a model for predicting chilling rates in the hams and loins of pork carcasses under blast chilling conditions.
The study utilized three temperature measurements (ambient, loin, and ham) from 753 carcasses for approximately 22 hours. Starting with the basic differential equation for Newton’s Law of Cooling, a model was developed to predict temperature decline over time in the ham and loin. The basic prediction equation was stable for the blast-chill portion (approximately 90 minutes) of the chill process but broke down when the carcasses were transitioned to the warmer equilibration coolers. By adjusting for an auto correlation issue in the data, a model was developed and validated that accurately predicted temperature decline for the ham and loin.
The model shows that though there appears to be a meaningful difference in the rate of temperature decline between heavy and lighter carcasses, loins achieve a deep muscle temperature approximately equal to ambient temperature prior to the end of the chilling period regardless of hot carcass weight. However, hams from carcasses 100 kg or heaver were warmer than hams from lighter carcasses at the end of the chilling period. For every 5 kg increase in hot carcass weight, the chilling rate of the ham’s semimembranosus muscle was reduced by 2%. Practically, this verifies and quantifies the observation that heavier carcasses require additional time to chill for the entire carcass to reach temperatures required for fabrication.
To view the full article, visit the Journal of Animal Science.