We’re talking about the chemistry of canning today on Good Things Utah, including Botulism, Dos and Don’ts, and Sugar Science.
How does sugar play a role in the canning process?
- The amount of sugar used when preserving fruit makes a huge impact on the overall quality of the ultimate preserve. Assuming acid levels are high enough, sugar is one ingredient you can safely change without fear of food safety. Sugar content of the syrup you use to pack your fruit will have the biggest impact on the long term quality of your fruit. Nature likes a balance, meaning the sugar content in your canning syrup needs to match the sugar content in your fruit, otherwise osmotic pressure changes the quality of your fruit. If your syrup is to sugary, the plant will push water out of your fruit into the syrup in an attempt to balance the sugar content. This creates shriveled fruit. If your syrup is not sugary enough, the fruit absorbs water from your syrup in an attempt to increase the overall sugar content. This causes your sugar to swell with water and create a water, bland preserve.
Considering that the sugar content of fruit changes daily, one would think it would be challenging for a home cook to know how much sugar to add to the canning syrup. Fortunately, there is an easy method to getting the syrup right. If the recipe has too much sugar, the fruit will float, whereas if it has too little sugar, the fruit will sink to the bottom of the jar. The trick to getting your syrup sugar content correct is simple, prepare your canning liquid as you normally would, but omit the sugar. Remove 1/4th of the canning liquid and add your sugar to the remaining 3/4ths. Add your sugary syrup to prepacked cans of fruit until the fruit starts to float. Then add non sugared water to the bottle until the fruit ceases to float, but doesn’t fall to the bottom. Continue this process until you have the appropriate amount of air (headspace) between your lid and fruit as determined by the recipe. (In general terms, the lower the acid, the higher the headspace).
What is Botulism?
- The botulism toxin is a byproduct of a thermophilic (likes heat) bacteria that thrives in low acid, low oxygen environments. Because it is not killed by normal boiling methods, It is the biggest threat to the home cook. A few things to keep in mind when canning in order to prevent botulism:
- Make sure your recipe is scientifically tested. Unfortunately, grandma’s recipes may not have the proper acid content to prevent the growth of Clostridium botulinum. When in doubt, call your local extension service for help. They are experts on the subject.
- Throw away any cans/bottles that are bulging, smelly or moldy. Although you can kill the Clostridium Botulinum bacteria if you have a pressure cooker, it doesn’t necessarily eliminate the botulism toxin. If you see a bulging can the botulism toxin is already in your food. Throw it away, it’s not worth the risk.
-When harvesting your garden, process your produce as quickly as possible as some fruits/veggies become less acidic. Tomatoes are particularly susceptible, as their acid content tends to decrease as they age.
What recipe modifications can I safely make to my canning recipe?
-Amount of sugar (assuming food has a pH of 4.6 or higher)
- Salt in recipes where it is only for flavoring, but not for preservation (pickle recipes, for example, use salt as a preservative)
-Adding MORE acid than the recipe calls for.
What should I avoid when canning?
Although the list for this particular question is by no means exhaustive (consult the USDA Complete Guide to Home Canning for a more thorough list), the following actions will create trouble in your preserves:
-Adding extra thickener to your recipe. This changes the thickness of your canned good, which ultimately changes the way heat works it’s way into the middle of your preserve. Thicker preserves take a LOT longer to cook.
-Use up to date methods. As of today, the USDA only recommends using water bath, and pressure canners.
-Cooking food for too short of a time period. The altitude in Utah means the boiling point is lower than sea level. Because of this, recipes need to be adjusted for a longer cooking time to create safe foods.
Good reference material for food safety guidelines:
USU Extension Service: http://extension.usu.edu/utah/htm/fcs/food-preservation-canning
Ball Blue Book of Preserving: http://www.amazon.com/Ball-Blue-Book-of-Preserving/dp/0972753702/ref=sr_1_1?ie=UTF8&s=books&qid=1278867370&sr=8-1
USDA Complete Guide to Home Canning: http://www.uga.edu/nchfp/publications/publications_usda.html
