De-tinning corrosion of cans filled with tomato products

Abstract

Several variables have been studied in four factorial experiments in order to determine their influence on the rate of de-tinning of cans containing tomato products, as follows: net weight; filling temperature; initial nitrate content; Brix value; pH; tinplate steel annealing; bodycorrugations; exposed steel; and some anions. Nitrates and net weight (i.e. residual internal air) were found to be the major factors influencing de-tinning; also, their effects were found to be independent and additive. In 500 g cans stored at 20° C for 24 months, the increase of dissolvedtin is proportional to nitrates and the net weight according to the estimated ratios:

Dissolved Tin/Initial Nitrate Content = 117 mg kg⁻¹/20 mg kg⁻¹

and

Dissolved Tin/Net Weight Change = −47 mg kg⁻¹/20 g

Technological considerationsabout the importance of Brix are discussed, and the predicted distributions of dissolved tin after 24 months are calculated for a simulated batch of 100 000 cans. According this model, the levels of 150, 200, 250 mg kg⁻¹ of tin content would be exceeded by 64%, 25%, and 4%, respectively,of cans filled with high Brix tomato products (6.5° Bx); in the case of the less aggressive ‘natural Brix’ products (5.0° Bx), the same levels of tin content would be exceeded by 42%, 6%, and 0.5% of the cans.