Firming additives are added to improve pickle firmness. Alum - aluminum compound forms a firmer pickle. Alum is no longer recommended by the USDA as some people were having digestive problems. The calcium in lime improves pickle firmness. Turmeric is often added to improve color. Adding chopped horseradish root helps to keep pickled cucumbers crisp. When fermenting at low temperature adding oak leaves to brine helps to prevent spoilage. Oak leaves contain tannin acid which keeps spoilage bacteria at bay until fermenting bacteria produce enough lactic acid for the sauerkraut to be stable.
Home made pickles develop soft texture due to the enzymes that are present. The best fix to the problem is soaking cucumbers for 12-24 hours in a solution of 1 cup of food grade lime to 1 gallon of water. Excess lime absorbed by the cucumbers is removed by draining cucumbers, rinsing and then re-soaking them in fresh water for 1 hour. This rinsing and soaking step should be performed two more times.