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Over the past several decades, beef carcasses in the United States have consistently become heavier with an increase in fat thickness. In the past decade alone, carcass weights have increased by over 60 pounds and backfat thickness has increased almost 0.5 cm. The increases in both fat thickness and carcass weights have led to questions on their influences of chilling rates, meat quality, and consistency of beef products. It is well known that chilling rates impact meat quality outcomes, however, it is not fully understood how chilling is impacted in the heavier and fatter carcasses and the subsequent influence on beef quality. The objectives of this project were to determine how beef hot carcass weights and 12th rib fat depth are related to temperature decline in the round during carcass chilling and determine subsequent impacts on tenderness, water holding capacity, and color stability.
Beef carcasses (N= 60) were selected for three levels of 12th rib fat thickness (thin [0.94-1.12 cm], average [1.19-1.82 cm], and fat [1.90-3.25 cm]) and three levels of carcass weight (light [302.1-361.1 kg], medium [365.1-408.5 kg], and heavy [412.0-508.5 kg]) at a large commercial packing plant in September 2022. Temperature of the deep portion of the round was measured for 24 hours. Upon completion of chilling, ribeye area, 12th rib backfat, kidney, pelvic, and heart fat percentage, marbling score, and calculated yield grade were collected. Tenderness, water-holding ability, and color measurements were collected on steaks from the top round and sirloin. Data were analyzed using the PROC MIXED procedure of SAS (SAS Institute, Cary, NC) with main effects of carcass weight and 12th rib fat depth and their interaction with carcass as the experimental unit. If the interaction was not significant, it was removed from the model. Means were separated using the PDIFF option and were considered significant when P ≤ 0.05.
Carcass weight influences temperature decline of the round, which is further influenced by 12th rib fat depth, but to a lesser degree. Even after 24 hours, the deep portion of the round on all carcasses was still at approximately 15°C. Fatter carcasses produced sirloin steaks that were lighter colored and less red than thin carcasses. Additionally, light weight carcasses produced sirloin steaks that were more red than medium and heavy weight carcasses. Otherwise, the display color of the top round steaks were not influenced by carcass weight or fat depth indicating the color was stable and most likely from the portion of the round that is more color stable. Conversely to the round steaks, the sirloin steaks had more variability in color. Sirloin steaks from fat carcasses were lighter colored on day 4 and maintained that tendency through day 5 and day 6 of display.
Carcass chilling rates are impacted by the continuous increase in carcass weights and fat depths. The impacts on meat quality traits are still not completely understood. However, color stability of some cuts is negatively impacted by heavier carcass weights and thicker fat depths. Once a greater understanding of how these increases in weight and fat influence primal, subprimal and retail cuts of importance, strategies can be developed to improve cooling rates in those specific cuts of interest in order help mitigate the negative outcomes on meat color.