Studies in Meat Tenderness.

TLDR: In this article, it was shown that very significant toughness develops in the longissimus dorsi muscles of lamb loin exposed to low temperatures within about 16 hr of slaughter. But this was unrelated to the lack of aging.

Abstract: SUMMARY— The tenderness of lamb loin is affected greatly by the time-temperature pattern imposed on the dressed carcazs during the onset of rigor mortis. Very significant toughness develops in the longissimus dorsi muscles of carcasses exposed to low temperatures within about 16 hr of slaughter. This “processing toughness” is shown to be unrelated to the lack of aging. It appears to be due to muscle fiber shortening, earlier demonstrated to be responsible for massive toughening in excised muscles. Both cold shortening and thaw shortening are capable of toughness production, the latter type becoming prominent when meat, previously frozen before rigor completion, is cooked without a preliminary thawing.