by Lloyd Arthur, Brett Kessler, and Suzy Cunningham
This web page was designed to inform 4-Hers, students, judging team members, producers, and consumers interested in knowing how a lamb gets from the processing plant to the grocery store.
There are several components of a carcass that allow for the determination of such things as age, maturity, and sex. All of these are taken into consideration when determining a quality grade.
Age and Maturity:
Age and maturity affect on another. More importantly, maturity characteristics can be used to determine the age of a carcass. Age is divided into three categories.
Lamb - 2 to 14 months of age
A lamb carcass can be identified by the presence of break joints on the front shanks. The joint is moderately red, moist, and porous. The ribs of the carcass will vary in shape from round to moderately flat with some redness on the exposed surfaces.
Young mutton - 12 to 25 months of age
A young mutton carcass is characterized by spool joints on both front shanks or one spool joint and an imperfect break joint. The ribs are moderately wind and tend to be flat with slight to no redness.
Mutton - over 24 months of age
Mutton carcasses always have spool joints. The ribs are wide, flat, and the color of mature bone. Flank muscles range in color from dark red to very dark red.
The break joint is a cartilaginous area of the cannon bone that is not
ossified. This joint ossifies with age to become what is called a spool joint.
Here are examples of a break joint on the left and a spool joint on the right.
There are also sex differences among carcasses. Ewe carcasses can be identified by the presence of an udder. In mutton, the udder is often "wet", having a yellowish brown exudate. If it is very wet, it will be removed during the harvesting process. Ewe lambs and yearlings have a pocket of udder fat the is long and smooth. Wethers have cod fat which is rough and irregular in shape. It is usually a smaller deposit that udder fat. Rams have the smallest fat deposit. They can also be identified by heavy shoulders and thick necks.
Before they are harvested, lambs are yield graded. This means that they are assigned a number value that allows livestock buyers to give the producer a price for the live animal. The buyer estimates the 12th rib fat of the lamb and plugs it into the following equation:
yield grade = .4 + (10 x 12th rib fat)
After harvesting, a yield grade is assigned to a carcass to reflect the
quantity of retail cuts expected from that carcass.
To measure the fat thickness, the carcass should be ribbed (cut) between the 12th and 13th rib. A ruler can be applied at the midpoint of each ribeye, the average is then determined.
A couple of other measurements that are not part of determining yield grade, but are important in evaluating the carcass include leg conformation score and ribeye area. Both indicate carcass muscling. Leg conformation score is a visual appraisal of the thickness of the carcass. Heavier muscled carcasses have a higher score. Ribeye area is measured by laying a grid of dots over the ribeye of a ribbed carcass. Both ribeyes are measured then the average is determined. 20 dots equal 1 square inch.
Quality grade is the expected eating satisfaction of lamb. Lamb quality grades are based upon palatability which is characterized by lean and carcass composition. For lambs and yearling mutton there are four quality grades: prime, choice, good, and utility. Older mutton quality grades include: choice, good, utility, and cull. The factors that affect quality grades include:
1: Maturity - This was discussed in the above section on determining age and maturity.
Lamb carcasses can be divided into A and B maturity groups. They are identified as follows:
Ribs moderately narrow, slightly flat slightly wide, moderately flat
Break joints moderately red, moist, porous slightly red, slightly dry and hard
Color of inside flank muscles
U.S. prime slightly dark pink light red
U.S. choice moderately dark pink moderately dark red
U.S. good dark pink slightly dark red
2: Flank Fat Streaking - Flank fat is a visible
deposit within and upon the surfaces of the primary and secondary flank muscles. It
is usually more extensive on the secondary muscle.
3: Firmness of Lean Flesh and External Fat - this is influenced by carcass fatness. The fattest lambs are the firmest in lean and fat while the leaner lambs are softer in lean and fat.
4: Conformation - Superior conformation carcasses are wide, thick, and heavy muscled. They will yield a higher percentage of edible portions. Carcasses poorer in composition are thinly muscled with a less desirable lean to bone ratio.
The following table shows the relationship to maturity and flank fat streaking that determine the quality grade of a carcass. Below is a group of lambs that were harvested. For the sake of space, only the carcass of lamb #1 is shown.
This is a live picture of lamb 1.
This is the view of lamb 1's ribeyes. The layer of fat closest to the bottom of the picture is the fat that is measured to determine backfat thickness.
There are four primal cuts on a lamb carcass. They include the shoulder, rack, loin, and leg. These cuts can be processed further. Below is an illustration of how the wholesale cuts are processed into retail cuts for consumers.
Here are some links to some other pages that offer lamb recipes. Enjoy!
Indian 4-H Sheep Project