Following on from this thread about Kilner jars, I thought I'd put up a short history of food preservation for those interested in growing and preserving their own food supplies.
History of Food Preservation
Necessity has long been the mother of invention. It was necessity which has led to the development of home preserving as we know it today.
The Beginning
Early in the nineteenth century, during the Napoleonic wars, the French army suffered disastrous losses due to starvation and bad weather conditions. To solve the situation, the French government offered a prize of 1200 francs for the invention of a food preservation process.
1809
N. Nicholas Appert, a confectioner, claimed the prize in 1809. Appert preserved meats, vegetables, fruits and even milk by placing them in widemouth glass bottles then carefully corking and heating them in boiling water. He paid meticulous attention to the quality of the foods to be canned and to the canning process. Appert observed that heat applied to foods sealed in a container, which was impervious to air, had the peculiar quality of preventing the food from spoiling. While he was correct in assuming that spoilage was caused by fermentation and the presence of air, Appert did not know that he was destroying microorganisms. In 1810, he published his famous work Le livre de tous les ménages ou l'art de conserver pendant plusieurs annees toutes les substances animales et végétales.
1819
Englishman Peter Durand conceived and patented the idea of using canisters made of thin sheets of steel instead of glass bottles.
1860
Frenchman Louis Pasteur proved that microorganisms were responsible for fermentation. Until this time, bacteria was not associated with food spoilage.
1895
H. L. Russell, working at the University of Wisconsin in the United States, connected bacteria growth with gaseous odours. He initiated the development of recommendations involving specific heat processing times and temperatures to destroy bacteria in specific foods.
1898
Spoilage of sweet corn was traced to imperfect sterilization by Prescotte and Underwood at the Massachusetts Institute of Technology.
Containers
Today's popularity of canned food both commercial and home canned foods can be attributed to refinements in the art of container manufacture cans, special glass jars and unique closures.
Kilner Jars
Kilner is the 'generic' name for a special type of glass jar designed for home food preservation. These jars are constructed of heavier weight glass than commercial food jars. Consequently, they can withstand processing temperatures in boiling water baths or pressure cookers and can be used many times. Kilner Jars are made by the Ravenhead Glass Company in England.
Unique Closures
Kilner in the U.K. and Bernadin and Mason in the U.S.A developed the first metal closure for commercial glass-pack canning. This invention lead to the establishment of the company which now carries their names. Kilner began producing a two-piece metal closure system for home canning.
Kilner's two piece metal lid consists of a screw band in combination with a Snap Lid. Two piece lids allow users to hear, see and feel an airtight seal on their home preserved products.
Over the years, Kilner has improved the profile of the lid as well as the performance of the sealing compound to enhance both the dependability and ease of handling of these unique closures. The snap lid is constructed of food-grade coated tin -- the top coating is an attractive gold lacquer with the underside being coated with a white acid-resistant enamel which comes in contact with the food. A groove in the underside of the lid contains the special sealing compound which is essential to form airtight seals.
Food Preservation - Science
Food is preserved by treating it to destroy spoilage factors or to create conditions in which they cannot grow. Methods available to accomplish this are: drying, canning and freezing.
Temperature
Home canning involves heating jars of food to temperatures high enough to destroy microorganisms and enzymes that may cause spoilage. In home canning, this step is known as heat processing. Processing not only destroys spoilage organisms but also drives air out of the jars. As jars of food cool, the contents of the jar contracts. Because air has been forced out of the jar, a vacuum forms, pulling the lid down onto the mouth of the jar and resulting in the formation of an airtight vacuum seal. This airtight seal keeps both air and microorganisms from re-entering the jar.
Once spoilage microorganisms are destroyed and the airtight seal has formed, jars of food processed by the appropriate method for the appropriate time can be stored at room temperature indefinitely.
Time & Temperature
Each food has a specific density which affects the rate at which heat penetrates to the centre of the jar. This heat penetration factor together with the size of jar affect the total amount of time and heat that must be applied during processing.
As the jar volume increases and/or the food density increases, processing time must also increase to reach the critical temperature in the centre of the jar. As temperature increases over 100°C, processing time decreases.
For example, crushed tomatoes--with the addition of acid like lemon juice--can be processed at 100°C in a boiling water bath for 35 minutes. In a pressure cooker, which reaches a temperature of 116°C at 10 lbs (68 kPa) of pressure, the required processing time decreases to 15 minutes.
Salt & Sugar
High concentrations of salt and sugar inhibit the growth of some spoilage microorganisms, however, some microorganisms are salt- or sugar-tolerant. Neither salt nor sugar alone are practical methods of food preservation. Salt or sugar concentrations high enough to inhibit spoilage would render the foods unpalatable. Salt and sugar resistant spoilage microorganisms must be destroyed by heat processing which also eliminates yeasts and moulds that can cause surface spoilage.
pH - Acidity
Acidity is very important. The level of acidity determines the processing method. Acidity level is not the amount of acid present as a percentage, but the acid strength. This is measured on a pH scale. The pH scale uses seven as the neutral point: pH values below seven are acidic; those above seven are alkaline.
High acid foods (pH values less than 4.6) can be safely processed in a boiling water canner. Low acid foods (pH values greater than 4.6) require processing in a pressure canner to destroy harmful bacteria.
High Acid Foods
All high acid foods may be processed in a boiling water canner. High acid foods include jam, jelly, fruit spreads, conserves, preserves, marmalade, fruits and fruit sauces, pickles, relishes, salsas, chutneys and tomatoes with added acid.
BOILING WATER BATHS
Boiling water baths are generally enamel coated and come equipped with a jar rack. A large, deep saucepan with a close fitting lid and a rack to lift jars off the bottom may be used if a boiling water bath is unavailable. Just be sure the pot is deep enough to allow jars to be covered with at least 2.5 cm (1 inch) water, and large enough to provide room for a full rolling boil.
Screw bands can be tied together with string to make a rack. Cake cooling racks also may be used. As an alternative to a saucepan, the bottom half of an old copper water storage tank can be used
Place filled jars in bath. Bring water to a full rolling boil; boil for the "processing time" specified in the tested recipe. Remove jars; let stand 24 hours, then check seals. Sealed lids curve downward. To prevent rusting, remove screw bands from sealed jar. Wash and dry screw bands and store separately for your next home preserving project.
1. Processing is necessary not only to destroy spoilage microorganisms, but also to create an airtight vacuum seal.
2. Processing destroys microorganisms that enter the jar upon filling. These microorganisms can cause food spoilage during storage at room temperature.
3. Exhausting the air from the jar is important! Oxygen left in the jar causes undesirable colour and texture changes to the food and can support microbial growth. Exhausting as much air as possible reduces the oxygen in the jar and results in a strong vacuum. Reducing the oxygen in the jar limits undesirable colour and texture changes and gives spoilage microorganisms little or no chance for growth.
Two-piece metal lids _ Snap Lids _ are necessary for every canning project. A unique sealing compound is built into the edge of the flat metal Snap Lid. When this compound is heated it softens, giving it the ability to fit snugly onto the rim of a jar. Use Snap Lids one time only. Once used, the sealing compound becomes less resilient and will not form itself onto a second jar rim. Screw bands may be reused.
Step by Step Home Canning HIGH ACID Foods
Home canning is simple and safe when you follow these easy Steps. Jams, jellies, marmalades, conserves, fruit butters, fruit and fruit sauces, tomatoes with added acid, pickles, relishes, chutneys and condiments are all processed in a boiling water canner.
Step 1
Always use the best, top quality ingredients. For the best results can fruits and vegetables when they are at peak quality. For most produce this means 6 to 12 hours after harvest.
Step 2
Wash Kilner jars in hot soapy water.
Step 3
Place Kilner jars and water in canner over high heat. For all recipes requiring less than 10 minutes processing time, sterilise jars before filling by boiling them at least 10 minutes in altitudes up to 1,000 ft (305 m).
Step 4
Boil Snap Lids 5 minutes to soften sealing compound and sanitise lids. Only the softened compound has the ability to fit snugly around the rim of the jar and form an airtight seal.
Step 5
Fill hot jar with prepared recipe.
Step 6
Leave proper "head space". This is the space left at the top of the jar between the underside of the Snap Lid and the level of the food or liquid. Overfilling and underfilling can cause seal failure. The amount of head space is determined by the type of food.
HEAD SPACE - High Acid Foods
Jam, Jelly --1/4 inch (0.5 cm)
Fruit -- 1/2 inch (1 cm)
Pickles, Tomatoes -- 1/2 inch (1 cm)
Relish, Chutney -- 1/2 inch (1 cm)
Step 7
Remove air bubbles by sliding a rubber spatula between jar and food. After removing air bubbles be sure to readjust head space to the level indicated in the recipe.
Step 8
Wipe jar rim removing any stickiness. Center Snap Lid on jar.
Step 9
Apply screw bands just until fingertip tight. FINGERTIP TIGHT allows some `give' between the Snap Lid and jar. This allows rising steam, created inside the jar during heat processing, to be exhausted.
Step 10
Process filled jars in boiling water canner for time specified in tested recipe. Start counting processing time when all jars are in the canner and water returns to a steady boil. (Adjust processing time for altitudes higher than 1,000 ft (305 m) above sea level.) When processing time is up, turn off heat and remove jars from canner; place on a wooden board, layers of newspaper or towels in a draft-free place. DO NOT RETIGHTEN screw bands.
Step 11/12
Cool jars 24 hours; check for vacuum seal. As the jars cool, the lids `snap' down creating an airtight, vacuum seal. Sealed lids curve downward. Remove screw bands and store separately. Label, date & store jars in a cool, dark place.
History of Food Preservation
Necessity has long been the mother of invention. It was necessity which has led to the development of home preserving as we know it today.
The Beginning
Early in the nineteenth century, during the Napoleonic wars, the French army suffered disastrous losses due to starvation and bad weather conditions. To solve the situation, the French government offered a prize of 1200 francs for the invention of a food preservation process.
1809
N. Nicholas Appert, a confectioner, claimed the prize in 1809. Appert preserved meats, vegetables, fruits and even milk by placing them in widemouth glass bottles then carefully corking and heating them in boiling water. He paid meticulous attention to the quality of the foods to be canned and to the canning process. Appert observed that heat applied to foods sealed in a container, which was impervious to air, had the peculiar quality of preventing the food from spoiling. While he was correct in assuming that spoilage was caused by fermentation and the presence of air, Appert did not know that he was destroying microorganisms. In 1810, he published his famous work Le livre de tous les ménages ou l'art de conserver pendant plusieurs annees toutes les substances animales et végétales.
1819
Englishman Peter Durand conceived and patented the idea of using canisters made of thin sheets of steel instead of glass bottles.
1860
Frenchman Louis Pasteur proved that microorganisms were responsible for fermentation. Until this time, bacteria was not associated with food spoilage.
1895
H. L. Russell, working at the University of Wisconsin in the United States, connected bacteria growth with gaseous odours. He initiated the development of recommendations involving specific heat processing times and temperatures to destroy bacteria in specific foods.
1898
Spoilage of sweet corn was traced to imperfect sterilization by Prescotte and Underwood at the Massachusetts Institute of Technology.
Containers
Today's popularity of canned food both commercial and home canned foods can be attributed to refinements in the art of container manufacture cans, special glass jars and unique closures.
Kilner Jars
Kilner is the 'generic' name for a special type of glass jar designed for home food preservation. These jars are constructed of heavier weight glass than commercial food jars. Consequently, they can withstand processing temperatures in boiling water baths or pressure cookers and can be used many times. Kilner Jars are made by the Ravenhead Glass Company in England.
Unique Closures
Kilner in the U.K. and Bernadin and Mason in the U.S.A developed the first metal closure for commercial glass-pack canning. This invention lead to the establishment of the company which now carries their names. Kilner began producing a two-piece metal closure system for home canning.
Kilner's two piece metal lid consists of a screw band in combination with a Snap Lid. Two piece lids allow users to hear, see and feel an airtight seal on their home preserved products.
Over the years, Kilner has improved the profile of the lid as well as the performance of the sealing compound to enhance both the dependability and ease of handling of these unique closures. The snap lid is constructed of food-grade coated tin -- the top coating is an attractive gold lacquer with the underside being coated with a white acid-resistant enamel which comes in contact with the food. A groove in the underside of the lid contains the special sealing compound which is essential to form airtight seals.
Food Preservation - Science
Food is preserved by treating it to destroy spoilage factors or to create conditions in which they cannot grow. Methods available to accomplish this are: drying, canning and freezing.
Temperature
Home canning involves heating jars of food to temperatures high enough to destroy microorganisms and enzymes that may cause spoilage. In home canning, this step is known as heat processing. Processing not only destroys spoilage organisms but also drives air out of the jars. As jars of food cool, the contents of the jar contracts. Because air has been forced out of the jar, a vacuum forms, pulling the lid down onto the mouth of the jar and resulting in the formation of an airtight vacuum seal. This airtight seal keeps both air and microorganisms from re-entering the jar.
Once spoilage microorganisms are destroyed and the airtight seal has formed, jars of food processed by the appropriate method for the appropriate time can be stored at room temperature indefinitely.
Time & Temperature
Each food has a specific density which affects the rate at which heat penetrates to the centre of the jar. This heat penetration factor together with the size of jar affect the total amount of time and heat that must be applied during processing.
As the jar volume increases and/or the food density increases, processing time must also increase to reach the critical temperature in the centre of the jar. As temperature increases over 100°C, processing time decreases.
For example, crushed tomatoes--with the addition of acid like lemon juice--can be processed at 100°C in a boiling water bath for 35 minutes. In a pressure cooker, which reaches a temperature of 116°C at 10 lbs (68 kPa) of pressure, the required processing time decreases to 15 minutes.
Salt & Sugar
High concentrations of salt and sugar inhibit the growth of some spoilage microorganisms, however, some microorganisms are salt- or sugar-tolerant. Neither salt nor sugar alone are practical methods of food preservation. Salt or sugar concentrations high enough to inhibit spoilage would render the foods unpalatable. Salt and sugar resistant spoilage microorganisms must be destroyed by heat processing which also eliminates yeasts and moulds that can cause surface spoilage.
pH - Acidity
Acidity is very important. The level of acidity determines the processing method. Acidity level is not the amount of acid present as a percentage, but the acid strength. This is measured on a pH scale. The pH scale uses seven as the neutral point: pH values below seven are acidic; those above seven are alkaline.
High acid foods (pH values less than 4.6) can be safely processed in a boiling water canner. Low acid foods (pH values greater than 4.6) require processing in a pressure canner to destroy harmful bacteria.
High Acid Foods
All high acid foods may be processed in a boiling water canner. High acid foods include jam, jelly, fruit spreads, conserves, preserves, marmalade, fruits and fruit sauces, pickles, relishes, salsas, chutneys and tomatoes with added acid.
BOILING WATER BATHS
Boiling water baths are generally enamel coated and come equipped with a jar rack. A large, deep saucepan with a close fitting lid and a rack to lift jars off the bottom may be used if a boiling water bath is unavailable. Just be sure the pot is deep enough to allow jars to be covered with at least 2.5 cm (1 inch) water, and large enough to provide room for a full rolling boil.
Screw bands can be tied together with string to make a rack. Cake cooling racks also may be used. As an alternative to a saucepan, the bottom half of an old copper water storage tank can be used
Place filled jars in bath. Bring water to a full rolling boil; boil for the "processing time" specified in the tested recipe. Remove jars; let stand 24 hours, then check seals. Sealed lids curve downward. To prevent rusting, remove screw bands from sealed jar. Wash and dry screw bands and store separately for your next home preserving project.
1. Processing is necessary not only to destroy spoilage microorganisms, but also to create an airtight vacuum seal.
2. Processing destroys microorganisms that enter the jar upon filling. These microorganisms can cause food spoilage during storage at room temperature.
3. Exhausting the air from the jar is important! Oxygen left in the jar causes undesirable colour and texture changes to the food and can support microbial growth. Exhausting as much air as possible reduces the oxygen in the jar and results in a strong vacuum. Reducing the oxygen in the jar limits undesirable colour and texture changes and gives spoilage microorganisms little or no chance for growth.
Two-piece metal lids _ Snap Lids _ are necessary for every canning project. A unique sealing compound is built into the edge of the flat metal Snap Lid. When this compound is heated it softens, giving it the ability to fit snugly onto the rim of a jar. Use Snap Lids one time only. Once used, the sealing compound becomes less resilient and will not form itself onto a second jar rim. Screw bands may be reused.
Step by Step Home Canning HIGH ACID Foods
Home canning is simple and safe when you follow these easy Steps. Jams, jellies, marmalades, conserves, fruit butters, fruit and fruit sauces, tomatoes with added acid, pickles, relishes, chutneys and condiments are all processed in a boiling water canner.
Step 1
Always use the best, top quality ingredients. For the best results can fruits and vegetables when they are at peak quality. For most produce this means 6 to 12 hours after harvest.
Step 2
Wash Kilner jars in hot soapy water.
Step 3
Place Kilner jars and water in canner over high heat. For all recipes requiring less than 10 minutes processing time, sterilise jars before filling by boiling them at least 10 minutes in altitudes up to 1,000 ft (305 m).
Step 4
Boil Snap Lids 5 minutes to soften sealing compound and sanitise lids. Only the softened compound has the ability to fit snugly around the rim of the jar and form an airtight seal.
Step 5
Fill hot jar with prepared recipe.
Step 6
Leave proper "head space". This is the space left at the top of the jar between the underside of the Snap Lid and the level of the food or liquid. Overfilling and underfilling can cause seal failure. The amount of head space is determined by the type of food.
HEAD SPACE - High Acid Foods
Jam, Jelly --1/4 inch (0.5 cm)
Fruit -- 1/2 inch (1 cm)
Pickles, Tomatoes -- 1/2 inch (1 cm)
Relish, Chutney -- 1/2 inch (1 cm)
Step 7
Remove air bubbles by sliding a rubber spatula between jar and food. After removing air bubbles be sure to readjust head space to the level indicated in the recipe.
Step 8
Wipe jar rim removing any stickiness. Center Snap Lid on jar.
Step 9
Apply screw bands just until fingertip tight. FINGERTIP TIGHT allows some `give' between the Snap Lid and jar. This allows rising steam, created inside the jar during heat processing, to be exhausted.
Step 10
Process filled jars in boiling water canner for time specified in tested recipe. Start counting processing time when all jars are in the canner and water returns to a steady boil. (Adjust processing time for altitudes higher than 1,000 ft (305 m) above sea level.) When processing time is up, turn off heat and remove jars from canner; place on a wooden board, layers of newspaper or towels in a draft-free place. DO NOT RETIGHTEN screw bands.
Step 11/12
Cool jars 24 hours; check for vacuum seal. As the jars cool, the lids `snap' down creating an airtight, vacuum seal. Sealed lids curve downward. Remove screw bands and store separately. Label, date & store jars in a cool, dark place.
