Optimum level of alum for sheep pelt tanning

Abstract

Development of sheep pelt tanning was done by using the pelts from 6 male fattening sheep with the average age of 14.6 ± 1.9 months and weighed 37.1 ± 4.0 kg. The pelt from each sheep which had an average area of 13.04 sq. ft/piece was divided into 4 parts. They were cleaned by removing the leftover meat, fat and membrane as much as possible. Eighteen completed pieces of the same size were chosen and randomly divided into 9 lots, each with 2 pieces. They were randomly allotted into 3 groups for soaking in 3 tanning solutions containing the same amount of 35% HCl, formalin (37% formaldehyde; CH2O) and table salt (NaCl), but varying amount of alum (Al2(SO4)3.xH2O), i.e., approximately 0.75, 1.0 and 1.25% (w/v), respectively. Each group was done 3 replications. After soaking in each tanning solution for 4 days, it was found that the more alum caused the higher acidity of tanning solution, i.e., 4.00 ± 0.10, 3.83 ± 0.06 and 3.77 ± 0.15, respectively. The solution containing 1.25% alum significantly caused lower pH than the 0.75% alum (P < 0.05), but not significantly differed from the 1.0% alum solution. There was no significant difference in pH of washing water among groups. Washing had to be done 3 times, each lasted 10 minutes of soaking, to get pH at around neutral (6.9). The pelts were then fixed in the wooden frames and were desiccated in the shade with good ventilation for 5 days. The pelt quality was evaluated using the 9-point Hedonic scale method. The 31 evaluators composed of 16 academic livestock officers, 5 buyers and 10 general consumers. It was found that the evaluators gave significantly overall preference on the tanning solutions which contained 1.0 and 1.25 to the 0.75% alum (P < 0.05). The scores were 7.87 ± 0.13 (1.0%) and 7.84 ± 0.16 (1.25%) vs. 7.42 ± 0.26 (0.75%), which being considered as “very like”. Pelt color, fur color, odor and texture of the pelt showed no significant differences among the 3 tanning solutions (P > 0.05). For the sake of saving cost, 1.0% alum is then suggested to be used in sheep pelt tanning solution.