Michigan State University Extension
Preserving Food Safely - 01600957
Alum may be safely used to firm fermented cucumbers. However, it is unnecessary and is not included in the recipes. The calcium in lime definitely improves pickle firmness. Food-grade lime may be used as a lime-water solution for soaking fresh cucumbers 12 to 24 hours before pickling them. Excess lime absorbed by the cucumbers must be removed to make safe pickles. To remove excess lime, drain the lime-water solution, rinse, and then resoak the cucumbers in fresh water for 1 hour. Repeat the rinsing and soaking steps two more times. To further improve pickle firmness, you may process cucumber pickles for 30 minutes in water at 180 degrees Fahrenheit when indicated by the procedure. This process also prevents spoilage, but the water temperature should not fall below 180 degrees Fahrenheit. Use a candy or jelly thermometer to check the water temperature.