The term 'pickling agent' refers to a substance used to preserve food by pickling. The most common pickling agents are BRINE, DILL, and VINEGAR. BRINE is a solution of salt and water that is used to preserve food. DILL is an herb that is often used in pickling recipes. VINEGAR is an acidic liquid made from fermented alcohol that is also used in pickling. All three of these substances can be used together to create a pickling solution.