Many people tend to use old preservative recipes for the purpose of canning food at home. Not all of these recipes are tested for their heat processing time and temperature. If you are planning to can fruits or vegetables at home, then it is safer to use modern methods.
Nowadays, food products that can be canned are classified as low-acid foods and high-acid foods. The methods recommended for both types of foods are different, because the temperature needed to neutralize these foods of harmful bacteria are different. Therefore, methods for canning tomatoes and beef are different. High-acid foods have a pH value of 4.6 or lower. Low-acid foods have a pH value higher than 4.6. High-acid foods, because of the high-acid content, resist harmful bacteria and micro-organisms better than low-acid foods.
A temperature of 240 degrees Fahrenheit is necessary to be maintained for a specified time, to can low-acid foods. Food products such as vegetables, poultry, soups, stews, meats, and seafood are classified as low-acid food. This task can be done well, using a steam pressure cooker. Using a boiling water-bath cooker for the same is not advised. Boiling water-bath cookers can be used for high-acid foods which need temperatures of 212 degrees. Fahrenheit to be maintained for a specified time. High-acid foods include fruits, fruit juices, jellies, and jams, etc.
Following are some methods used to cure and preserve high-acid and low-acid foods. Instructions for preserving high-acid foods follow. Further, they can be easily preserved and are therefore, favored.
- Inspect your equipment i.e. boiling water-bath cooker, jars, lids, spatula, etc.
- Gather all the ingredients that are mentioned in the recipe, go through the recipe and keep in mind the time needed to process the food items. Choose the jars of the correct dimensions to store the food prepared.
- Inspect your jars and lids for scratches and dents, while also making sure that once sealed, they will remain so. Discard unsuitable jars and lids. Use hot water and soap to rinse them.
- Place all the jars along with their lids in water, and heat it to 180 degrees Fahrenheit to sterilize them. After doing so, keep them in hot water, to be ready to use.
- Prepare the food that you have planned on. Fill the jars with the food prepared one at a time.
- Take the jar out of the hot water as and when needed. Taking all jars out of the hot water at the same time would defeat the purpose of sterilization.
- Don't fill the jar with food up to the brim. There must be space between the underside of lid of jar and its contents.
- Use a non-metallic spatula to stir the contents of the jar to let the trapped air out.
- Clean the rim and threads of the jar to remove food residue. Apply sealing paste along the rim of the jar and fix the lid. Seal the jar, using a sealing band but make sure you do not fasten it too tight. This will allow the air to escape, during the next step of processing.
- When you have sufficient number of jars to fill the boiling water-bath cooker or when you have exhausted your foodstuff, place them on the rack in the boiling water-bath cooker.
- Fill the cooker with water and immerse the jars in it. Close the cooker and maintain heat at medium.
- Start counting the processing time, when the water starts boiling. Allow for extra time, if you are canning the food 1,000 feet above sea-level.
- After it is done, turn down the heat and open the cooker. Allow the boiling water to cool down and then lift the jars out of it, while taking care not to tilt any of them.
- Place them in a locked room, undisturbed for 24 hours. Check the cooled jar's lids, for perfectness of the seal. If you press down on the center of the lid, and it does not budge, then it is sealed well. Store the jars with faulty seals in the refrigerator, or repeat the process.
- Store the jars with the perfectly sealed lids in a cool place and consume the contents within a year.
For canning low-acid food items, a steam-pressure canner is ideal.
- Check steam-pressure canner's lid and gasket for faults and if need be, replace them. It needs to be air-tight.
- Inspect the jars and lids and sterilize them using hot water. Prepare the food by following instructions given in the recipe.
- Fill the jars with food one by one. Let the trapped air out of jars, using a spatula as before. For low-acid food items maintain one-inch of head space.
- Place it over high heat, after pouring 2-3 inches of water in it. After the water starts boiling, place the jars containing the food items in it.
- Close the lid, leaving the steam vent open. Maintain heat to medium-high and allow the steam to escape through the vent-pipe. After ten minutes, close the vent. By adjusting the heat, maintain pressure as prescribed.
- After it is done, turn down the heat. Leave it undisturbed, till the pressure of the steam in it drops to zero.
- Remove the jars after opening the canner and leave them undisturbed for 24 hours.
- Test them to check if they are perfectly sealed. Store the jars with perfect seals in a cool place and those with faulty seals, in the refrigerator. Consume the contents within a year.
Using the 'open-kettle' method is as good as inviting trouble. It is not a secure method of food preservation. If bacteria or micro-organisms grow in the cans because of overripe food items, outdated methods or just lack of precaution, it could lead to food poisoning. Go through these instructions and take care, while preparing canned food, so that your efforts are well rewarded.