Marbling

Marbling is the intramuscular fat that shows as fine white streaks on the cut surface of meat. It is the main criterion for grading beef quality and is assessed on the cross-section of the longissimus muscle in the rib area.

The USDA sorts beef into eight quality grades according to marbling and physiological maturity of the animal. Prime requires at least “slightly abundant” marbling, Choice “small” to “moderate” and Select “slight”; the assessment is made where the carcass is cut between the 12th and 13th ribs.

The Japanese marbling scale has 12 grades and is read between the 6th and 7th ribs, where a Canadian study found on average about a third more intramuscular fat than at the North American grading site, so grades from different systems cannot be compared directly. Dry aging is recommended for beef with at least “modest” marbling.