A bacteriological study of ham souring

by Charles Neil McBryde

To the meat inspector, a sour ham is one which has a tainted or “off” odor, that is, any odor which deviates from the normal. The odor may be very slight, so slight that at times only the trained meat inspector can detect it. When slight, the odor is elusive and hard to define, but when pronounced it has a distinctly putrefactive quality. When not very pronounced, the odor possesses, as a rule, a slightly sour quality, chemically speaking, and at times this sour quality may be quite marked; hence the term “sour ham,” or “sour” has originated. In a badly soured ham—using the term “sour” in the packing-house sense to denote any ham that is tainted—the odor loses this sour quality and becomes distinctly putrefactive in nature.

CLASSIFICATION OF SOUR HAMS AND LOCATION OF SOUR AREAS.

Sour hams are classed as “shank sours” and “body sours,” according to the location of the souring, and these may be “light” or “heavy.” When the souring is very pronounced, the ham is termed a “stinker.”

Souring appears to start, as a rule, around the stifle joint (femorotibial articulation), and extends upward into the body of the ham.

In quite a large proportion of the hams which are sour in the body—probably from 40 to 50 per cent—the souring extends through to the bone marrow of the femur or middle bone, and the sour odor is at times more pronounced in the bone marrow than in the meat. The odor of the bone marrow, when pronounced, is strongly suggestive of a dissecting-room odor, and is distinctly putrefactive in quality.

In the case of light body sours the sour odor is confined to a small area immediately around the bone, and may be so slight that it is detected only with difficulty. In such hams the bone marrow is apt to be sweet, and it is not until the souring becomes more extensive that the bone marrow becomes involved.

Fig. 1.—Cross section through body of ham, with sour areas indicated by shading and dotted lines.

The distribution of the sour area in the body of a well-developed sour is shown in figure 1.

In the case of a well-developed body sour the sour area is more pronounced near the bone, as represented in figure 1 by the shaded area, and may extend out into the body of the ham for a variable distance, according to the degree of souring, as represented by the dotted lines, gradually fading off toward the margins, where it may be imperceptible or entirely wanting.