The Process of Canning Vegetables


Canning VegetablesOne of the most undeniable contributions to our present day fast-food life is the canned food. Canned chickpeas, canned tomatoes, canned tuna! Entertaining a guest at home has never been easier. Emergency travel has become less stressful, all thanks to the canning industry.


The Canning Story:


However, the story behind the introduction of canning to our modern world is fascinating. Not many of us are aware of it, but take for granted that it is something our grandmothers used to do. True, but it was Napoleon Bonaparte who thought of the need to preserve and can food and thereby inspired the process of what we call "Canning".


The French Revolution (1975) resulted in the Napoleonic Wars, with malnutrition and starvation the common scenes among the soldiers. This affected the status of the wars and became a critical factor in determining the victory or loss of a battle. . Napoleon knew that the success of his many battles depended upon good food provided for his army, and therefore he ran a contest for anyone who could find a way to preserve food in bulk.


Nicholas Appert, a candy maker in Paris filled glass jars with vegetables in it, hermetically sealed the lids on and placed the jars in a bath of water, bringing it to boil for a while. This process came to be known as Appertisation and was the first recorded incident in the history of canning. Appert won 12,000 francs for his effort and for about a decade this was a French secret. Napoleon won many a war because of it. By 1810, the English grabbed on to the canning phenomenon and by 1812, Thomas Kensett opened the first canning factory in New York, USA.


Today, canned food has become a vital part of our diet. Even pet food is canned! The introduction of canning brought with it a whole new world of jams, jellies, pickles and preserves.

Canning is a very simple process of storing and preserving food yet requires the utmost care in doing so. The usual domestic canning materials are the glass jars (that can be immersed in water and brought to boil) and the various types of canners.


The Canning Process:


Canning is a process of packing and storing (preserving) food in jars, subject to sterilization under heat.


In order to can vegetables (as in this case), we should first understand the basics of the preservation process. Vegetables contain micro-organisms on the outside and enzymes on the inside. The one-celled micro-organisms called bacteria and many types of yeast and mold can result in many diseases if present other than for the process of fermentation. Enzymes are proteins in vegetables that affect the taste, color, smell and overall freshness, and bring about deteriorating changes to the vegetables over time. For these reasons, the process of canning adopts the steps of blanching (of the vegetable) and sterilization (of the filled, sealed jar).


Canning is based on identifying two basic types of food: low acid foods and high acid foods.


Low Acid Food:


Almost all vegetables are low acid foods, even at times tomatoes, if not too acidic. Low acid foods harbor the bacterium Clostridium botulinum (causing botulism, a nerve toxin) which is not killed even at boiling point of water and hence has to be killed at a minimum temperature of 240 degrees Fahrenheit (115.5 degrees Celsius). This bacterium, if not killed can thrive, grow and multiply even at temperatures just below 240 F and cause high food toxicity over a period of time. For this reason, jars with processed food of low acid content are heated in a pressure canner, where the temperature reaches 240 F and kill the bacteria.


High Acid Food:


Tomato and figs are examples of high acid foods. For these items, treating them to a temperature equivalent to the boiling point of water is enough (212 degrees Fahrenheit / 100 degrees Celsius). Microorganisms contained in high acid foods are easily killed in boiling water; hence, a water bath sterilization of the filled jars will suffice.


Pressure Canner:


A pressure canner is very similar to a pressure cooker and works on the same principle. It reaches very high temperatures, except that pressure canners come with a canning rack. The rack is in place to hold and immerse the jars into the water. A 16-quart pressure canner can hold up to 7 quart jars.


Water Bath Canner:


Water bath canners are steel vessels of differing measurements used for high acid food and contain a rack for the jars. This canner can be used without the lid and the water has to be brought to boiling point and made to bubble for a minimum of five minutes.


Some Common Canning Terms:


  • Ascorbic Acid: Vitamin C especially in lemon fruits. Used to prevent browning of vegetables during canning.
  • Canning: A method of sterilizing and preserving air-tight-vacuum-sealed containers so as to store them at room temperature.
  • Canning salt: Pickling salt, or salt without iodine.
  • Hermetic seal: An airtight bottle seal, when used, seals off contents of the jar from being exposed to external microorganisms, bacteria and air.
  • Canning rack: A rack for holding jars which are immersed into a pressure canner or a water bath canner.
  • Jar Lifter: Tongs used to remove the jars from the canner.
  • Magnetic picker: A small, magnet-tipped rod that is used to pick up sterilized jar lids from the outside, so as not to contaminate the lids.


There are many recipes that can be used for canning. However, care should be taken in following the canning recipe guidelines and also in the use of the pressure canner.


Articles in this series:

How to Dry and Store the Vegetables You've Grown

How to Freeze and Preserve the Vegetables You've Grown


Image Credit: Canned Vegetables from Wikimedia Commons