Snails are mature when a lip forms at the opening of their shell. Before they mature, their shells are more easily broken, making them undesirable. For H. aspersa, commercial weight is 8 grams or larger.
The nutrient composition of raw snails (per 100 grams of edible portion), according to information from the nutrient databank of France, is:
* Energy: 80.5 kcal (337 kJ)
* Water: 79 g
* Protein: 16 g
* Available carbohydrates: 2 g
* Fiber: 0 g
* Fat: 1 g
* Magnesium: 250 mg
* Calcium: 170 mg
* Iron: 3.5 mg
* Vitamin C: 0 mg
Snails are washed, steamed, shelled, then washed in a vinegar- (or lemon juice) and water-solution before they are canned. Producing a quality canned product is somewhat tricky, and you must take care to prevent food poisoning.
To prepare live snails for cooking, remove the membrane, if any, over the shell opening. Soak the snails in enough water to cover them. (Add 1/2-cup salt or 1/4-cup vinegar for every 50 snails.)
Mucus will turn the water white. Change the water several times during the 3- to 4-hour soaking. Rinse several times or under running water until no mucus remains. Put snails in cold water and bring to a boil.
Boil about eight minutes, then drain and plunge the snails into cold water. Drain. With a needle or small fork, pick the snails out of their shells. Remove the intestine and cut off all black parts. (Some cooks also cut off the head, tail, and all "cartilage or gristle.") Prepare according to your recipe. An alternate method is: Wash the snails well in clear water. Drop into boiling salt water (to which you may add lemon juice and/or herbs), and cook--about 10–15 minutes--until you can easily remove the snails from their shells. Drain and rinse.
Prepare the giant African snail by breaking away the shell, then cutting the foot away from the rest of the body. The traditional way to remove the slime is to rub wood ashes on the snail, then wash the snail (or part of the snail) under running water, then repeat until no slime remains. You may substitute substances like flour (to which you may add salt and vinegar) for ashes. Cut up the foot into convenient-sized pieces. [You may dehydrate the leftover visceral mass, crush it up with the shell, and mix it in poultry feed to make up 10% of your snail feed.]
Another source says put the live snails in boiling water for 30 minutes to kill them and to make removal from the shell easy. During boiling, the snails will release a large quantity of mucus. Data varies, but 28% to 46% of the live weight of Achatina is shell.