Typically, processing tomatoes are peeled by chemical lye peeling (using
NaOH or KOH), steam or scalding-hot water. These three methods remove the
cuticle and some of the most external cell layers of tomatoes. Overpeeling is
a problem frequently associated with improper lye peeling, in which many
layers of tomato flesh are removed resulting in an undesirable light red color
and exposure of some superficial yellowish vascular bundles. In addition to
this undesirable appearance, overpeeling leads to poor yield; therefore, operations
must be closely monitored to ensure removal of peel without excessive
flesh loss. Moreover, the use of lye peeling may create a waste disposal
problem that may be both deleterious to the environment and costly (Schlimme
et al. 1984; Corey et al. 1986).
Mechanical systems of peeling, which employ primarily steam or hot
water, on the other hand, offer the advantage of being safe for the environment.
In California, about 70% of processing tomatoes are peeled with either steam
or hot water, and the remaining 30% are lye peeled. However, the use of lye
peeling is increasing. Yields are commonly higher with lye peeling, and the
cost of waste disposal is not prohibitive. In the Midwest region of the U.S.,
chemical peeling is the most commonly used method (Das and Barringer
1997).