Tag Archives: preventing foodborne illness

Freezing Soups and Stews A Good Wintertime Activity

It is still chilly and winter in most locations. Even here in Georgia we are still swinging between chilly and warm. Today would have been my mother’s birthday and that reminds me of how she loved to use her freezer for convenience in meal preparation.

There is nothing like a hot bowl of homemade soup or chili on a chilly winter’s day. But not everyone has time or ingredients to make it when the mood strikes or it’s time to eat. Just imagine having a freezer full of delicious, homemade meals ready to be heated and served when you get home from work. Freezing prepared foods in advance allows you the satisfaction of homemade meals with the convenience of store-bought ones. A lot of people have gone the route of instant cookers and fast preparation, but for some, making ahead and just reheating is even a quicker answer.  (Believe me, I also have my favorite stovetop soups that cook up quickly, even with lots of flavor, but that does require I have the ingredients on hand when the mood strikes.)

There are just a few things to keep in mind when freezing prepared foods. Freezing will not improve the texture, flavor, or quality of most food. It simply acts to preserve the quality of the food. Therefore, you should only freeze high quality ingredients. Some ingredients may not hold up well in the freezer, especially if you don’t plan to use it quickly this season only. You can look up some cautions and effects of freezing on spices ahead of time (http://www.uga.edu/nchfp/how/freeze/dont_freeze_foods.html).  Other tips for freezing prepared foods can be found from the University of Georgia also (http://www.uga.edu/nchfp/publications/uga/FreezingPreparedFoods.pdf).

After cooking the food you plan to freeze, be sure it is cooled quickly to maintain the safety of the food. You can quick-cool your hot soups or stews by stirring in a bowl or pan that is set down into an ice bath.  Never leave perishable food at room temperature more than two hours; if you do not quick-cool it until cold enough to put in the freezer, put the food in the refrigerator to finish cooling.

Be sure to put your soup in moisture-vapor resistant packaging to prevent freezer burn.  Now what does that mean?  We see it all the time. You want packaging that doesn’t allow for moisture from the food to be drawn out into dry air through it.  And you want packaging materials that keep odors inside the pack. Not all plastics and foils are the same in these characteristics, for example. For soups and stews, rigid containers like freezer quality plastic boxes or jars are a good choice; freezer-weight plastic bags can be used, just a little more awkward to fill and seal with runny food.

To make the most of the convenience factor, package your soup or stew in amounts that you will be able to eat at one time.  Be sure to clearly label each package with the name of the food, and date you put it in the freezer. If you have a variety of foods that will look alike and have short names on that label, consider including some ingredients on that label.  Be sure all sealing areas are clean and dry and to leave recommended headspace for expansion inside the package (https://nchfp.uga.edu/how/freeze/headspace.html). Once packaged and sealed, and place in the coldest part of the freezer.

Quick, it’s time to eat! You can put your soup or stew in a pan for stovetop or bowl for microwave and cook right from the frozen stage. If you heat in your freezer container, make sure it is intended to be used for the hot temperatures the cooked food will reach. Be sure to stir to prevent burning on the stovetop and to evenly distribute heat with either method of cooking. Thawing in the refrigerator is safe, but takes some planning ahead. You can also thaw in the microwave even if you finish cooking on a stovetop or oven.  And reheat your food to at least 165°F everywhere quickly, within 2 hours of starting.  (If I have a broth-based soup that can be brought to a visible boil, I always do that myself to ensure adequate reheating.) If you want to quick-thaw under cold running water, be sure the package is leak-proof and keep running water moving slowly over the package or place it in a clean pan or bowl and submerge under cold tap water that is changed every 30 minutes. Be sure to reheat as above as soon as the food is thawed enough.  To ensure the safety of your food, do not allow these potentially hazardous foods to stay in the temperature danger zone (40°F-140°F) for more than 2 hours at any time.

Planning ahead and freezing that favorite soup, stew or chili is a great way to keep homemade food on your dinner table without all of the stress and hassle of last minute cooking from scratch.

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Why Can’t I Just Guess at a Process Time for Canning?

Mold on JamIf you guess at a process time for canning, you run the risk of underprocessing your food, which could lead to food poisoning and/or product loss due to spoilage.

All reliable recommendations for canning include process times that have been determined by or based on results of laboratory testing. The exact time and temperature combinations of tested canning processes are needed to assure the destruction of microorganisms that may be present in the filled jars. Sure, it’s possible that you could use unsafe canning practices for some time without causing waste or harm, but it only takes one batch of food with destructive microorganisms in it to ruin your streak of luck. And especially if you are canning low acid foods, the consequences could be severe and irreversible.

While some microorganisms are apparent just by looking (think molds growing on the surface of jelly), others remain invisible to your bare eyes (think pathogenic bacteria which cause food poisoning). Many different types of mold, yeast, and bacteria dwell on food. Given their preferred conditions of moisture, acidity, oxygen levels, and temperature they will grow, and some will even product toxin.

Fortunately, all microorganisms can be destroyed by breaking their threshold for heat. The process times provided in each of our home canning recommendations have been found to deliver enough heat to destroy microorganisms of concern in that particular food. Characteristics such as consistency, pH level (acidity), size of food pieces, presence of protective nutrients, size and shape of jars, and solid to liquid ratio all influence the ability of heat to move through and thoroughly penetrate the entire contents of a filled jar. You can trust that your home-canned foods will receive adequate heat treatment by using proper canning methods and following recommended process times.

Why does each recipe have a process time table with multiple times or amounts of pressure? (See Crushed Tomatoes for a good example.) Because atmospheric pressure decreases as altitude increases, causing water to boil at lower temperatures as altitude increases. In order to achieve the same overall heat treatment as at sea level, more time is needed in a boiling water canner at higher elevations (since the temperature of the water distributing the heat is less). Pressure canning relies on temperatures inside the canner building even higher than that of boiling. So, likewise, more pressure needs to be applied to a pressure canner at higher elevations so that the temperature inside can reach higher.

If you’d like to learn more about how process times are determined for home-canned foods, please read ‘Backgrounder: Heat Processing of Home-canned Foods’ by Elaine M. D’Sa.

Botulism: Think Outside the Jar

Since it’s that time of year that foods may be prepared well ahead of time, then packaged and transported to be shared with family, friends, and co-workers, it seems timely to spread awareness about less-known situations that have the potential to lead to botulism: Did you know that it is possible for botulism to come from non-canned food items? As mentioned in a previous posting called “Botulism: Surprises”, botulism has been linked to other foods, including unrefrigerated salsa, baked potatoes in aluminum foil, garlic in oil, fermented fish, and honey. Following are a few true tales to provide important details and inspire caution…

In 1994, in Texas, 30 people were affected by an outbreak of botulism from restaurant dips made with baked potatoes wrapped in foil and left at room temperature (apparently for several days) prior to being used the dips. In this case, the spores of Clostridium botulinum (which are readily found in soil) survived the heating process (which is to be expected), remained moist, and were then so tightly wrapped in aluminum foil that oxygen was kept out of the packaging, creating an anaerobic environment in which the botulism toxin could form. Oil covering a food, as with garlic in oil, also creates an anaerobic environment.

real potatoes

Not even processing your homemade salsas but putting them in tightly sealed jars (again, an anaerobic environment) left at room temperature is a big risk. Botulism could result if the salsa is too low in acid, and other problems besides botulism could occur even in more acid salsas. Tomatoes (and figs and Asian pears) are borderline pH foods, so we see recommendations to add some acid to jars even before treating them as boiling water canned foods. Fermented fish and fermented vegetables that do not finish fermenting to a truly acidic pH are other examples of foods that might not be acidic enough to prevent the botulism-causing toxin from forming.

Another situation that has caused botulism is pickled eggs left at room temperature. In 1997, in Illinois, a 68-year-old man developed symptoms of botulism – double vision, inability to speak, difficulty breathing – that was traced back to homemade pickled eggs. Testing confirmed the presence of type B botulism toxin. To prevent the toxin from forming, pickled eggs should be stored in the refrigerator and only be at room temperature for serving time; limit their time in the temperature danger zone (40 degrees F to 140 degrees F) to no more than 2 hours. Pickled egg recipes and storage guidelines can be found on the NCHFP website.

Early in 2011, two people got botulism from eating commercially made potato soup intended for refrigerator storage but kept in their homes at room temperature.  One case was in Georgia and one in Ohio.  Both people bought the soups from a refrigerator case, left them out of the refrigerator at home for a long time and then tasted them.  Bad decision!  Each individual spent a long time in the hospital and then were transferred to rehab facilities with respiratory issues. Unfortunately we do not know the ultimate outcome today.

It may now seem like botulism can come from anywhere, but that’s not true; Clostridium botulinum bacteria require specific conditions to be able to grow and produce the botulism-causing toxin. Understanding what’s involved in the formation of the toxin will help you know how to prevent it:

In order to grow and produce the botulism-causing toxin, C. botulinum bacteria must be kept in a very low-oxygen (anaerobic) environment with a pH above 4.6 (low acid foods) and a relatively high moisture content.  If these conditions are met, any temperatures in a wide range around anyone’s “room temperature” and definitely above 40 degrees F will allow the bacteria to multiply and produce toxin.  (Sometimes the temperature even can be a little cooler than that for some types of C. botulinum and they will still multiply.)

Pressure Canner

Awareness and action is the key to prevention. To avoid botulism, avoid the risk of containing C. botulinum in a low acid, moist, anaerobic environment and if you do so (you canners out there know who you are), then be sure to process your low-acid food products in a canner equivalent to at least 240 degrees F (achieved when your pressure canner reaches the recommend amount of pressure, after venting, for your altitude) for the recommended amount of time.

Click here to view the full article of ‘Foodborne Botulism From Eating Home-Pickled Eggs —Illinois, 1997‘ from the Centers for Disease Control and Prevention. Here is the full publication ‘A Large Outbreak of Botulism: The Hazardous Baked Potato‘.  And here is the short story of botulism from potato soups in 2011.  

Why can’t I can what companies can?

As a home canner looking for new recipes to try out, you might sometimes be inspired by commercial products found on grocery shelves. But even after scouring through all your recipe books, magazines, and online resources there are still some products for which you cannot find home canning recommendations. Why is this? What do these companies have that you don’t?

Well, in summary, companies have two things that home canning does not have: 1) special equipment and 2) lots of money for research.

Commercial facilities have industrial equipment that can reach higher temperatures more quickly than what can be achieved at home. With specialized equipment, they are also able to control the consistency and maturity of ingredients. This control reduces the variability of the canning process, which allows for more reliable research (and therefore more product development) than can be done for home-canning practices.

Companies pay to conduct expensive research in order to determine safe product formulas and processing methods for each and every product. Even if just one ingredient is added to an already approved product, that new recipe must be carefully tested before being manufactured for sale. Acidity levels, water activity, and heat penetration are all critical factors influencing processing times, and these factors vary greatly among different recipes.

Proper studies to establish processing times for both commercial and home-canned recipes are crucial to the safety of canned foods. Without proper processing times, there is significant risk of botulism resulting from under-processed canned foods, especially low acid foods. Experimentally determining safe processing times requires a lot of time and money, and there is no easy formula to take into account the way that each product heats in each canning situation. Commercial and home-canning processes are not interchangeable. That is why there are fewer recipes and processes for home canning than many people would like.

For more information about heat processing of home-canned foods, read this ‘Backgrounder’ by Elaine M. D’sa.