This article will concentrate on glass jars equipped with screw-on lids, often referred to as twist-off caps, offering valuable insights and advice for preparing your preserves or ready meals.

Glass jars for preserves and ready meals

Glass jars are the most commonly used containers for gourmet preserves and, in general, within the food industry. This is due to its large opening (or mouth), which allows all kinds of products to be packaged inside it with greater convenience, including whole solid products such as fruits or vegetables.

The history of glass jars is linked to the material from which they are made. Since the invention of the first machine for the automatic manufacture and mass production of glass containers in the early 1900s, the use of this type of container has increased drastically.

Prior to this innovation, preservation techniques were limited and not always effective, restricting the availability of certain foods when they are out of season or making long-term storage difficult. The ability of glass to create an airtight environment, along with it’s compatibility with the sterilization process, revolutionized the way food could be preserved.

This evolution coincided with the growing need to store and transport food on a large scale, driven by urbanization and population growth. Glass jars, thanks to their durability, reusability and non-reactive properties, became an ideal solution to tackle this challenge. In addition, the transparency offered by glass containers allows consumers to see the contents, which adds a confidence and quality factor to the product.

Over the years, glass jar manufacturing technology has advanced significantly, improving the efficiency and safety of this method of preservation. Today, these containers are not only essential for the food industry, but they have also earned a special place in the homes of people seeking to preserve the quality and flavor of their homemade preparations.

Main characteristics of glass jars used for food products

Nowadays, we can find an infinite number of different designs of glass jars, with different formats and capacities and different opening sizes, etc.

Each country has its own regulations and a limited and accepted variety of glass jars, classified according to their diameter or sealing ring and capacity.

Although glass containers can be produced in a wide variety of shapes, there is a large repertoire of standardized designs in the packaging industry.

Regardless of their shape, all glass jars have some basic parts:

The opening or mouth
The neck, where the threads and the transfer or locking ring are located.
The shoulder
The body
The push-up or kick-up, which is the concave-shaped surface inside the jar.
The bottom

The most common closures for this type of containers are screw caps (or twist off). These caps have nails on the inside which, in combination with the threads, allow the closure of jars.

The caps are made of steel or tinplate, varnished on the outside to protect the metal and with a neutral sealant (usually polymers) on the inside.

Remember, not every glass jar and lid is made to endure high-temperature processing.

It’s crucial to understand the processing method you plan to use for your preserves when selecting containers. There are caps specifically designed for pasteurization, which can tolerate temperatures up to 90°C, and others made for sterilization, capable of withstanding up to 121°C.

What kinds of food are typically stored in glass jars?

Glass jars are used for solid and semi-solid foods as well as for liquids. The most common foods packaged in glass jars are:

Advantages and disadvantages of using glass jars for preserves

One of the first benefits we highlight is the material from which the container is made.

Glass, an inert substance, does not impart any flavor to its contents and can be reused indefinitely. While producing and handling glass is costlier and more fragile compared to other materials, it is widely regarded as safer and more environmentally friendly.

From an aesthetic point of view, glass is more pleasant, since its transparency shows the product inside and generates greater consumer confidence.

On the other hand, it should be noted that glass jars are characterized by a large diameter opening, which facilitates the packaging of solid or semi-solid foods.

A minor drawback is the screw cap; however, this issue is easily addressed. Leaving an empty space at the top of the container, a hermetic seal is achieved that prevents food from escaping through the joint during thermal processing in an autoclave, , which could otherwise lead to spoilage and contamination of the equipment and other containers.

How to produce preserves and ready meals in glass jars

First, you must prepare your product, which may be packaged either raw, semi-cooked, or fully cooked. Then, it must be placed in the glass jars. Before filling, ensure the glass jars are sterilized.

If the product is raw or cooked, you must leave an empty space between the food and the cap to avoid setbacks. If your product is composed of pieces, you will have to add a covering or governing liquid (water, sauce or oil) so that the temperature can be optimally transmitted.

Next, perform the necessary heat treatment, allow the jars to cool to room temperature, and then move on to labeling

Remember that the choice of container doesn’t dictate the heat treatment method: decide between pasteurization or sterilization depending on the type of food and the desired shelf life.

In general, most foods in glass jars undergo sterilization, since this type of container withstands high temperatures quite well.

Useful tips for the sterilization of food in glass jars

For selecting the ideal glass jars for your gourmet preserves or ready-to-eat meals, it’s advisable to opt for jars with minimal curvature and a small shoulder area. This design ensures easier cleaning and more convenient filling of the jars.

On the other hand, depending on the ingredients of your canned food, it is possible that your product may show a slight darkening on its surface. This is quite normal and does not affect the quality of the product at all. If you are interested in concealing this aspect so that it does not give a wrong impression, we recommend that you place the label of your canned food covering the dark areas.

Back pressure plays an important role in the outcome of the container characteristics. In glass jars with metal lids, it prevents the cap from opening during processing and also creates a vacuum inside the jar. The vacuum effect can be customized and is directly related to the force required to open the jar. In addition, it will allow an easy visual inspection of the correct processing of all containers by observing the curvature of the caps.

How do TERRA Food-Tech® autoclaves enhance the sterilization process for your glass jars?

The different characteristics of TERRA Food-Tech^® autoclaves for sterilizing glass jars make a small equipment a great production partner that is cost-efficient, fast and versatile.

Adjustable F₀ - P₀

Pasteurizes or sterilizes accurately using F₀ and P₀ values

Fast cooling

Fast cooling by water shower to avoid overcooking the product

Adjustable counterpressure

Programmable counterpressure value according to the type of container

Traceability for audits

Manage and record the process from start to finish with our software

Precise control

Continuous process monitoring thanks to the flexible temperature probe

Protection

Excellent safety measures for the user and his products

Are you looking to enhance the production efficiency of your preserves or prepared meals business?

At TERRA Food-Tech^®, we assist you in assessing the productivity you can achieve with various models and types of containers.

The insights from these analyses prove invaluable when choosing the most appropriate autoclave model for your project.

Such evaluations remain beneficial even after acquiring an autoclave, as they enable us to understand how production capacity may vary with changes in container size.

Moreover, we design tailor-made baskets and racks to suit the specific requirements of your business.

Need some inspiration? Dive into the success stories of our customers who utilize glass jars.

Many of our customers have opted for glass jars to package their gourmet preserves or ready meals. In our success stories section you will find several examples of companies that produce preserves in glass jars with our autoclaves.

Luca Montersino

Training and processing of food and confectionery products

CuorMio®

Canned food production for dogs and cats

Pibernat

Preparation of preserves made from meat, fish, sauces and sauteed foods

La Spigola

Production of artisanal preserves of fish and other products

Quattro Stagioni

Artisan preserves workshop

Tilberedt

Preparation of stews, vegetarian dishes and canned sweets

Looking to learn more about the sterilization of glass jars with TERRA Food-Tech^® autoclaves? Contact our experts today

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