Post by Gaz on Aug 31, 2016 12:12:17 GMT 10
Why use a pressure canner over a water bath Method?
Botulism. Just the word is enough to put a terrified expression on the faces of people, and with good reason. But armed with some facts about this scary bacterium, you will never have to worry about it when you're canning food at home.
How dangerous is botulism? Very. You can't see it, smell it, or taste it, and just one teaspoon of the botulism toxin that is produced by Clostridium botulinum would be enough to kill hundreds of thousands of people.
Yikes.
Fortunately, there are some very simple ways to make absolutely certain that botulism is a non-issue in your home-canned foods.
As far as canning methods go, you need to remember that non-acidic foods must be processed in a pressure canner, not a boiling water bath. That will make sense once you know the
"why" behind the "what."
Although a brisk boil destroys botulism bacteria and toxins, it is not hot enough to destroy the spores. Now if you're going to eat the just-boiled food right away, that's okay. But if those spores are going to sit in a jar of incorrectly canned food on a shelf at room temperature, that could be a deadly problem.
What do I mean by "incorrectly canned"? I mean that something that should have been pressure canned was processed in a boiling water bath instead. The reason that is so important is that a pressure canner heats the food to hotter than the temperature of boiling water. It gets the food all the way up to 240F/116C, which is hot enough to kill botulism spores.
Here's why canning non-acidic foods in a boiling water bath is dangerous: The processing temperature in a boiling water bath cannot get hotter than 212F/100C, the temperature of boiling water at sea level. So the bacteria are destroyed, but not the spores that can grow into more bacteria.
Clostridium botulinum spores grow in an environment that has no air, is a temperature between 70F/21C and 110F/43C, and includes more than 35 percent moisture. Sound familiar? That's right - it's exactly the environment inside a canning jar of food stored in a kitchen cabinet at room temperature.
But the good news for home canners is that botulism is wiped out by food that has an acidic pH. That translates into the happy fact that you can safely process pickled vegetables, sugar preserves, and fruits in a boiling water bath (which you can do with a regular stock pot).
Temperatures below freezing as well as moisture levels below 35 percent also render botulism inactive, which is why it isn't a concern with frozen and dehydrated foods.
To sum up:
Vegetables that are not pickled, soup stocks including vegetable stocks, and all animal products must be canned in a pressure canner.
Acidic pickled veggies, jams, jellies, chutneys and fruits can be processed in a boiling water bath. Tomatoes may also be processed in a boiling water bath if you add a little acid in the form of vinegar, lemon juice, or citric acid.
Frozen and dehydrated foods are safe from active botulism bacteria and spores.
Acidity Determines Processing Times
Whether you should process food in a pressure canner or boiling-water canner to control botulinum bacteria depends on the amount of acid in the food. The term "pH" is a measure of acidity. The lower the pH, the more acid the food.
Acid foods include pickles, most fruits and jams and jellies made from fruit. (In pickling, the acid level is increased by adding lemon juice, citric acid or vinegar.) Acid foods contain enough acidity either to stop the growth of botulinum bacteria or destroy the bacteria more rapidly when heated.
Low-acid foods don't contain enough acid to prevent the growth of botulinum bacteria. Process these foods at temperatures of 240 degrees F to 250 degrees F. To reach these high temperatures, you must use a pressure canner operated at 10 to 15 pounds per square inch of pressure (PSI). The exact time depends on the kind of food being canned, the way it is packed into jars and the size of jars.
Low-acid foods include red meats, seafood, poultry, milk, all fresh vegetables and some tomatoes. When you mix low-acid and acid foods, assume that the mixture remains low-acid.
Although tomatoes used to be considered an acid food, some are now known to have pH values slightly above 4.6, which means they are low-acid. To safely can them as acid foods in a boiling-water canner, you must add lemon juice or citric acid.
Adjust For Altitude To Ensure Safety
It's important that you know your altitude.. Don't use process times recommended for canning food at sea level if you live at altitudes above 1,000 feet. Water boils at lower temperatures as altitude increases. Lower boiling temperatures are less effective for killing bacteria. You must increase either the process time or canner pressure to make up for lower boiling temperatures.
Because altitude affects pressure and the boiling point of liquid, adjustments must be made when canning foods at altitudes of 1,000 feet above sea level or higher. When using the boiling water bath method, processing time must be increased. Add 5 minutes to processing time for altitudes between 1,000 and 6,000 feet above sea level. When using the pressure canner method, pressure must be increased. If using a dial-gauge pressure canner, process foods at 12 pounds pressure for altitudes between 2,000 and 4,000 feet and at 13 pounds pressure for altitudes between 4,000 and 6,000 feet. If using the weight-gauge pressure canner, use 15 pounds of pressure rather than 10.
Botulism. Just the word is enough to put a terrified expression on the faces of people, and with good reason. But armed with some facts about this scary bacterium, you will never have to worry about it when you're canning food at home.
How dangerous is botulism? Very. You can't see it, smell it, or taste it, and just one teaspoon of the botulism toxin that is produced by Clostridium botulinum would be enough to kill hundreds of thousands of people.
Yikes.
Fortunately, there are some very simple ways to make absolutely certain that botulism is a non-issue in your home-canned foods.
As far as canning methods go, you need to remember that non-acidic foods must be processed in a pressure canner, not a boiling water bath. That will make sense once you know the
"why" behind the "what."
Although a brisk boil destroys botulism bacteria and toxins, it is not hot enough to destroy the spores. Now if you're going to eat the just-boiled food right away, that's okay. But if those spores are going to sit in a jar of incorrectly canned food on a shelf at room temperature, that could be a deadly problem.
What do I mean by "incorrectly canned"? I mean that something that should have been pressure canned was processed in a boiling water bath instead. The reason that is so important is that a pressure canner heats the food to hotter than the temperature of boiling water. It gets the food all the way up to 240F/116C, which is hot enough to kill botulism spores.
Here's why canning non-acidic foods in a boiling water bath is dangerous: The processing temperature in a boiling water bath cannot get hotter than 212F/100C, the temperature of boiling water at sea level. So the bacteria are destroyed, but not the spores that can grow into more bacteria.
Clostridium botulinum spores grow in an environment that has no air, is a temperature between 70F/21C and 110F/43C, and includes more than 35 percent moisture. Sound familiar? That's right - it's exactly the environment inside a canning jar of food stored in a kitchen cabinet at room temperature.
But the good news for home canners is that botulism is wiped out by food that has an acidic pH. That translates into the happy fact that you can safely process pickled vegetables, sugar preserves, and fruits in a boiling water bath (which you can do with a regular stock pot).
Temperatures below freezing as well as moisture levels below 35 percent also render botulism inactive, which is why it isn't a concern with frozen and dehydrated foods.
To sum up:
Vegetables that are not pickled, soup stocks including vegetable stocks, and all animal products must be canned in a pressure canner.
Acidic pickled veggies, jams, jellies, chutneys and fruits can be processed in a boiling water bath. Tomatoes may also be processed in a boiling water bath if you add a little acid in the form of vinegar, lemon juice, or citric acid.
Frozen and dehydrated foods are safe from active botulism bacteria and spores.
Acidity Determines Processing Times
Whether you should process food in a pressure canner or boiling-water canner to control botulinum bacteria depends on the amount of acid in the food. The term "pH" is a measure of acidity. The lower the pH, the more acid the food.
Acid foods include pickles, most fruits and jams and jellies made from fruit. (In pickling, the acid level is increased by adding lemon juice, citric acid or vinegar.) Acid foods contain enough acidity either to stop the growth of botulinum bacteria or destroy the bacteria more rapidly when heated.
Low-acid foods don't contain enough acid to prevent the growth of botulinum bacteria. Process these foods at temperatures of 240 degrees F to 250 degrees F. To reach these high temperatures, you must use a pressure canner operated at 10 to 15 pounds per square inch of pressure (PSI). The exact time depends on the kind of food being canned, the way it is packed into jars and the size of jars.
Low-acid foods include red meats, seafood, poultry, milk, all fresh vegetables and some tomatoes. When you mix low-acid and acid foods, assume that the mixture remains low-acid.
Although tomatoes used to be considered an acid food, some are now known to have pH values slightly above 4.6, which means they are low-acid. To safely can them as acid foods in a boiling-water canner, you must add lemon juice or citric acid.
Adjust For Altitude To Ensure Safety
It's important that you know your altitude.. Don't use process times recommended for canning food at sea level if you live at altitudes above 1,000 feet. Water boils at lower temperatures as altitude increases. Lower boiling temperatures are less effective for killing bacteria. You must increase either the process time or canner pressure to make up for lower boiling temperatures.
Because altitude affects pressure and the boiling point of liquid, adjustments must be made when canning foods at altitudes of 1,000 feet above sea level or higher. When using the boiling water bath method, processing time must be increased. Add 5 minutes to processing time for altitudes between 1,000 and 6,000 feet above sea level. When using the pressure canner method, pressure must be increased. If using a dial-gauge pressure canner, process foods at 12 pounds pressure for altitudes between 2,000 and 4,000 feet and at 13 pounds pressure for altitudes between 4,000 and 6,000 feet. If using the weight-gauge pressure canner, use 15 pounds of pressure rather than 10.