Canning Essentials. Jackie Callahan Parente

processing is moderate and there’s no cost for storage.

       Cons: The initial investment for a pressure canner is somewhat costly. In addition, foods experience some flavor and nutrition loss compared to freezing. Pressure canning takes longer and is slightly more complicated than water-bath canning and freezing.

      Corn is one of many vegetables that should be pressure-canned. To can corn, you’ll need to cut it off the cob (individual recipes will explain how to do this).

      FOLLOW THE RULES

      Be sure to follow the recipes exactly, without adjusting the ingredients, proportions, type of processing, or processing time. For extra guidance, check with your local Cooperative Extension Service or USDA Guides to Home Canning and Preserving.

       SPOILAGE: SIMPLE BIOLOGY AND CHEMISTRY

      Safe home food preservation is simply a matter of obeying the rules of biology and chemistry. If left to nature, food will spoil, become inedible, and possibly transmit bacteria. This is caused by naturally occurring processes and organisms. Home food preservation involves identifying them and creating environments that stop or retard the processes and destroy the organisms so that the food remains safe to eat. If you’ve looked into home food preservation, you’ve surely heard about food that has spoiled and had to be discarded—or worse, horror stories about food poisoning and botulism. The truth is that some preserved food does spoil; on very rare occasions, this causes serious consequences. That’s why it’s very important to understand the mechanics of food spoilage and to always follow safe food-preservation practices. There is no one more vested in the safety of your food than you are!

      Thoroughly washing your produce is one of the most important steps to creating a delcious and healthy product.

       HOW ACID AND HEAT WORK TOGETHER IN FOOD PRESERVATION

      If you’re around food preservation circles it won’t take long before you hear folks talk about high-acid and low-acid foods. This is a fundamental concept in food preservation because it serves as an index for measuring whether a particular food will provide a friendly or unfriendly environment for the invasion of microorganisms that cause food spoilage. The portion of this discussion that deals with high-acid and low-acid foods applies to canned foods only, not to frozen foods.

      Like all creatures, the microorganisms that cause food spoilage are looking for a happy place to live and multiply. Many of them like it warm but not too warm. That’s why we refrigerate our food—to delay spoilage. Some are sensitive to the amount of acid in a food. Most need some oxygen to thrive, which is why we seal the jars that we process. But some, such as the dreaded bacterium that causes botulism, prefer no oxygen. This can make things a bit tricky. Understanding how microorganisms respond to heat, moisture, acid, and air helps us understand which food preservation method will be best for us.

      Some recipes will call for blanching vegetables (boiling or steaming and then rapidly cooling them). One of the reasons for blanching is to kill off some harmful microorganisms.

      HOT STUFF

      First, let’s look at how different microorganisms are affected by heat. See the table “Processing and Storage Temperatures for Food Preservation” for an illustration. There are three things that can cause your food to spoil: enzymes, fungi (molds and yeasts), and bacteria.

       Enzymes promote the changes that are a necessary part of that plant or animal’s life cycle. Eventually, however, these enzymes change the food’s color, flavor, and texture and make it unappetizing.

       Molds are fungi that grow on foods and look like fuzz. Some molds are harmless, but many more are not. These harmful molds produce mycotoxins, which can cause illness, and they thrive in high-acid environments, meaning they may eat the acid in a food that would otherwise protect that food from spoilage by bacteria. Molds are easily destroyed when heated to temperatures between 140 and 190 degrees Fahrenheit.

       Yeasts are fungi that cause food to ferment. This fermentation—while good in certain circumstances, such as those used in making pickles, bread, and beer—will often make food unfit to eat. As with molds, yeasts are easily destroyed when heated to temperatures between 140 and 190 degrees Fahrenheit.

       Bacteria are very different and can be more difficult to destroy. Some bacteria, notably the dreaded Clostridium botulinum, which causes deadly botulism poisoning, require a low-acid environment to live but can withstand temperatures much higher than yeasts, molds, and enzymes. As we said earlier, some bacteria thrive in environments where there is no oxygen. So, sealing the jar on these guys would just make them happy. And, bacteria produce spores, which—if not killed during processing—become bacteria that produce deadly toxins. While some bacteria will die at the same temperature as yeasts and molds, those pesky spores are much more resilient and require significantly higher temperatures to succumb.

      PROCESSING AND STORAGE TEMPERATURES FOR FOOD PRESERVATION

TEMPERATURE	FOOD’S RESPONSE TO TEMPERATURE	DESCRIPTION
240°F	• This temperature kills bacteria and spores found in all food. • This is the only safe temperature for processing low-acid food.	This is the temperature you need to reach when pressure-canning.
150–212°F	• These temperatures kill most molds, yeasts, and bacteria in high-acid food, but they don’t kill bacterial spores. • Higher temperatures decrease the time needed to kill microorganisms.	Water-bath canning reaches 212°F, and the average simmer begins at 190°F.
40–140°F	Danger! Between 40 and 140°F, bacteria, yeasts, and molds grow rapidly in unpreserved food.	95°F is the highest safe storage temperature for canned foods. Around 50°F is the best storage temperature.
32°F	Bacteria, yeasts, and molds grow slowly at cold temperatures.	Water freezes.
-10–0°F	Microorganisms do not grow in freezing temperatures, but some survive.	This is the ideal temperature for freezer storage.
-10°F