Bactericidal Methods


    Bactericide means to kill or completely eliminate bacteria in food.  The bactericidal methods in food preservation are cooking (and its various methods), canning, pasteurization, irradiation, and sterilization.  Each of the following method's advantages and disadvantages were explored along with the appropriate steps to complete each process of preserving food.

~ Table of Contents ~

Washing

Cooking
    Boiling & Stewing
    Frying
    Grilling
    Pressure Cooking
    Baking
    Microwave Cooking

Canning
    Pressure Canning
    Water bath Canning

Irradiation & Sterilization

Pasteurization

Applicable Methods in Third-World Regions

Advantages

Step-by-Step Procedure

Links

~ WASHING ~

Before you even begin any of these methods, the very first step is to wash the food to get rid of dirt, micro-organisms, helminthic ova or cyst, insecticide etc.  However, do not wash or soak the fruits and veggies too long since the water soluble vitamins and minerals will be lost.
 

~ COOKING ~

Cooking is the most commonly used food preservative method. This also improves digestibility, taste, flavour, and appearance.  Cooking methods include:  boiling and stewing, frying, grilling, pressure cooking, baking, and microwave cooking.

To boil food, simply immerse a food in a boiling salted liquid, generally water.  If boiling temperature is maintained long enough, then most of the bacteria and spores are killed.  The disadvantages of boiling is the loss of vitamins (B&C) and minerals that are water soluble.  Therefore, use only adequate amount of water and for the required time.  Also use leftover water as stock for soup. To cook food in fat over moderate to high heat.  Shallow frying is preferable compared to deep
frying.  Deep frying at high temperature will produce toxic chemicals such as peroxides, aldehydes, ketones, hydroperoxidases, cyclic monomeres etc.  Preferably avoid reusing the fried oil. One of the ancient methods of cooking.
1.) To cook on a grill.
2.) Cooking equipment in which the heat source (gas, charcoal, hardwo or electric) is located beneath the rack on which the food is placed; it is generally not enclosed, although it can be covered.
Disadvangtage is that it can have a carcigenic effect if burnt on coals and fire. Uses a cooking pot made to cook food under pressure.  The pressure cooker has a locking lid and a valve system to regulate the internal pressure.  The advantages of this method are the cooking time may be reduced by as much as 50% and it requires less water, preserving the nutritional value of the food. Cooking in an oven, surrounding the food with dry heat of a specific temperature.  The advantage is that large quantities of food can be cooked. There is not much loss of nutrients and food is easily digestible. The microwave works when the high voltage is converted to waves of electromagnetic energy, which is a combination of electrical and magnetic energy. This energy is in the frequency band of radio waves, not x-rays.  The microwaves make the water molecules contained in food vibrate and 'wiggle', which produces heat.   As soon as the microwave energy is absorbed by the food, it is converted to heat - so the microwave energy can't 'contaminate' the food.  Although heat is produced directly in the food, microwave energy doesn't cook food from the inside out. More dense foods like meat are cooked primarily by conduction of heat from the outer layers, which are heated by microwaves.  The main disadvantage of this method is that it is not readily available in rural regions of third-world countries.
 

~ CANNING ~

There are two types of canning:  one uses a pressure canner and the other, simpler method uses a water bath canner.  The water bath method is explored more extensively than the pressure canner method since it is a more viable option for preserving food in rural parts of developing countries.
 

To begin this method, cleaned, sterilized (boiled) jars are filled with hot high-acid food. The jar rim is wiped clean. A hot, boiled new lid is placed on the jar. And a clean ring is screwed firmly onto the jar. The filled jars are then placed carefully in the boiling water bath of the canning kettle and settled into an individual place on the wire rack. When filled, the water level needs to be one to two inches above the top of the tallest jars. The cover is put on the kettle and it is allowed to return to a full rolling boil, at which time the processing time is begun.  At the end of the processing time each jar is carefully lifted out and placed on dry folded towels where sealing will occur as the jar cools. Usually you can hear the loud, musical ping as each jar seals.  Leave the jars alone until they are cool. Don?t wipe, poke or move them, or you may end up with an incomplete seal. And do not screw the rings tighter thinking it will ?help? the jar to seal. Tightness doesn?t equal good sealing. It happens due to the vacuum caused by the processing.
 
 

Answers about canning
Complete guide to home canning (warning: PDF)
 
 

~ Irradiation & Sterilization ~

Food irradiation is the use of ionizing radiation or ionizing energy to treat foods, either packaged or in bulk form. Ionizing radiation may come from one of three sources - radioactive isotopes of cobalt or caesium, electron accelorators or X-rays. All three sources produce similar effects since they all fall in the short-wave, high energy region of the spectrum.

Sterilization is a non-thermal treatment for pathogen reduction and enzymatic deactivation in liquid foods. The introduction of this processing technology to commercial applications has been inhibited by the lack of electronic systems capable of delivering economically, the sufficient high levels of power required to treat thousands of liters of liquid per hour.

*These methods are mainly commercialized operations and are not viable options for third-world countries.  They are simply defined and linked on this webpage.

    guide to food irradiation
    everything you ever wanted to know about irradiation
    good news and more tidbits about food irradiation
    pulified electric field steriliation

~ Pasteurization ~

Any milk intended for human consumption should be strained.  Pasteurization is a bacteria-killing process that kills germs.  Convenient electric pasteurizers are available that you simply plug in or you can use a double boiler set-up and pasteurize on your stovetop. Use a thermometer and heat the milk to 161 degrees Fahrenheit. Stir milk to be sure it is 161 degrees throughout, then hold at this temperature for 20 seconds. Remove the milk from the heat and cool quickly by placing in ice water.

definition, purpose, and methods of pasteurization
do it yourself
 

~ Applicable Methods in Rural Regions of Third-World Countries ~

For all of the above food preserving methods, a source of heat is the critical element needed.  Without it, we could not even begin the process.  Where there is no electricity in many remote regions of the world, people rely on fire as their primary source of heat for warmth and cooking.  So, if people are already using fire to cook the food they can obtain now, then why not use fire to preserve food for later use?  Some of these methods will be more feasible in different parts of the world, depending on access to markets for various supplies.  However, if you have a heat source and a pot for boiling water, then you can begin preserving food.
 
 


photo courtesy of Kraig Lothe, RPCV from Nepal






Methods that could be viable include:

1. boiling and stewing
2. frying
3. grilling
4. canning - water bath method
5. pasteurizing

~ Advantages ~

Each food preserving method keeps food edible for a certain amount of time.  Obviously the cooking methods are used for immediate consumption or stored up to a few days, depending on the type of storage.
Nutrients that are needed year round are only available during certain times of the year can be preserved for the off season.  However, canning is a simple solution to a very serious problem since it is a great method to keep food preserved for several months and even years.
 

~ Step-By-Step Procedures ~

Canning

1.  clean and sterilize jars by placing them in boiling water
2.  fill with hot high-acid food
3.  wipe jar rim clean
4.  place a new boiled lid on the jar
5.  screw a clean ring firmly onto the jar
6.  carefully place the filled jars in the boiling water bath of the canning kettle and allow to settle into individual place on the wire rack
7.  make sure the water level is one to two inches above the top of the tallest jars
8.  put the cover on the kettle and allow it to return to a full rolling boil, at which time the processing time is begun
9.  at the end of the processing time, carefully lift out each jar and place them on dry folded towels where sealing will occur as the jar cools (usually you can hear the loud, musical ping as each jar seals)
10.  leave the jars alone until they are cool
 

Pasteurizing

1.  use a double boiler set-up to pasteurize on stovetop or over fire
2.  use a thermometer and heat the milk to 161 degrees Fahrenheit
3.  stir milk to be sure it is 161 degrees throughout
4.  hold at this temperature for 20 seconds
5.  remove the milk from the heat and cool quickly by placing in ice water.
 

~ Links ~

Cooking
http://www.bawarchi.com/health/food-preserve1.html
http://www.artcopperware.com/main/dictionnaire/a_langlaise_index.html
http://southernfood.about.com/library/info/bld_f.htm
http://www.reynoldskitchens.com/reynoldskitchens/kitchenconnection/ka/cooking_dictionary/dictionary_results.asp?SEARCHCRIT=G
http://southernfood.about.com/library/info/bld_p.htm
http://www.reynoldskitchens.com/reynoldskitchens/kitchenconnection/ka/cooking_dictionary/dictionary_ults.asp?SEARCHCRIT=B
http://busycooks.about.com/library/howtos/blmicrowave101.htm

Canning
http://www.fcs.uga.edu/pubs/current/FDNS-E-37-3.html
http://www.backwoodshome.com/articles/clay53.html
http://www.ext.nodak.edu/extnews/askext/canning.htm
http://www.extension.usu.edu/publica/foodpubs/canguide/cangui0.pdf
 

Irradiation and Sterilization
http://www.food-irradiation.com/basics.htm
http://www.food-irradiation.com/florida.htm
http://www.eatright.org/adap0200.html
http://www.divtecs.com/food/FOOD.HTM

Pasteurization
http://www.foodsci.uoguelph.ca/dairyedu/pasteurization.html
http://www.backwoodshome.com/articles/shaffer64.html