target="_blank" rel="nofollow" href="#fb3_img_img_ca6735b7-3dc2-5505-8bd3-1895f0591e66.jpg" alt="Illustration"/> 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 | This temperature creates a sharp freeze. | This is the ideal temperature for flash-freezing foods. |
HOW ACID FITS IN
The next component in canning is the acid level, or pH. Foods that are high in acid (acidic) call for different (some might say easier) means of preservation than foods that are low in acid (alkaline). See the table “Acidity and Safe Food Preservation” for some specific fruits and vegetables, but as a rule of thumb, fruits (including tomatoes) are high in acid while vegetables and meats are low in acid. Acidity is measured on a scale of pH values from 1 to 14, with 1 being the most acidic and 14 being the most alkaline. The midpoint on that scale (7) is neutral, but for our purposes, the tipping point is a pH level of 4.6. Thus, if a food has a pH value of 4.7 or higher, it will require different processing than foods that are 4.6 or lower. Note: Foods with a pH value of 4.7 or higher cannot be safely processed in a water-bath canner.
ACIDITY AND SAFE FOOD PRESERVATION
| TYPE OF SPOILAGE AGENT | MAXIMUM PH LEVEL THAT AN ORGANISM WILL SUSTAIN | TYPE OF FOOD | METHOD OF CANNING |
| 1 (Strongly Acidic) | |||
| Molds | 2 | ||
| Yeasts | 3 | LemonsPicklesApricotsPlumsApplesPeachesSauerkrautPears | High-Acid Foods:safe to processat 212°F in awater-bath canner |
| 4 | Tomatoes | ||
| Bacteria | 4.6 | Highest pH level that is safe to water-bath | |
| 5 | FigsOkraCarrotsBeetsGreen BeansSpinach | Low-Acid Foods:safe to processat 240°F in apressure canner | |
| 6 | |||
| 7 | Corn | ||
| Peas | |||
| 14 (Strongly Alkaline) |
TAKE BABY STEPS
When you try a new recipe, start small. Even recipes from reliable sources may not work out as well as you’d hoped. Just as you’ve tried recipes from great cookbooks and find that you simply don’t like the way a recipe tastes, or that it doesn’t look like the picture, the same can be true for any of the recipes involving food preservation. First time around, make just one batch. You’ve heard this before, but it’s worth repeating: if you are a novice, start simply. Try water-bath canning or freezing. Freezing green beans is a snap (pun intended) and the results are great! Canning tomatoes or peaches is easy. Making strawberry freezer jam is even easier, but cooked jam is a breeze, too. You’ll find recipes for these in the following chapters. Yes, it’s tempting to want to triple the recipe or try something exotic. But starting small and simple helps you to quickly find what works best for you, and then grow your new skills with confidence.
PUTTING THEM TOGETHER
Now let’s bring together the two key factors of acidity and heat. Remember, the high versus low acid determination only impacts food preserved by canning. If you are freezing food, acidity is irrelevant.
