Jam is a preserve made primarily from cooked fruit and sugar, born from the need to extend the shelf life of fruits and vegetables beyond their harvest season or as an alternative way to market produce with less visual appeal.

In this section, we’ll discuss the benefits of making jams as well as the considerations to keep in mind when sterilizing or pasteurizing them—all while preserving that puree-like texture, with or without fruit pieces, that’s so characteristic of these delicious recipes.

Jam: A delicious way to make the most of fruits and vegetables

Jam is created by turning fruit or certain vegetables into a pulp through cooking, adding sucrose, glucose, acid, and sometimes gelling agents and organic colorants.

Besides being a delicious way to enjoy fruits or vegetables, making jam is also a practical way to use:

Fruits or vegetables that are not suitable for sale due to quality or appearance.
Surplus produce.
Seasonal products, when supply is higher and prices are better.

This way, even when a fruit or vegetable is out of season, you can still enjoy a tasty jam.

Producing canned jams offers a great business opportunity for farmers, allowing them to create a new revenue stream with surplus fruit. It’s also beneficial for chefs, who can use seasonal fruits and vegetables—at their peak flavor and best prices—to make jams that can be used in their dishes or sold to customers.

Jam consumption

According to ReportLinker, a portal compiling key market statistics, the demand for jam has grown by an average of 1.5% per year since 2016, with European jam consumption expected to reach around 2.2 billion kilograms by 2026.

France is the largest jam market in Europe, with 962 million kilograms consumed in 2021. Germany, Spain, and Poland follow as major European consumers. Portugal has seen the highest year-over-year growth, with an 8% increase.

While jam can be a delicious way to enjoy fruits and vegetables, it’s best to consume it in moderation due to its high sugar content, ranging from 45% to 65%.

The high glycemic index of jam causes sharp spikes in blood glucose levels, which, over time, can increase the risk of type 2 diabetes, obesity, and cardiovascular diseases.

As a result, there is a growing trend toward reducing the amount of sugar or sucrose in jam products or using alternative sweeteners.

Fun fact:

Did you know that ancient Greek and Roman civilizations were already making preserves with honey and quince? However, it wasn’t until the Middle Ages that a method similar to today’s jam and jelly-making process began to be used.

Types of jams

While there isn’t an official classification for jams, this is a good opportunity to introduce and clarify the differences between four very similar foods that have distinct nutritional profiles:

Jam

A preparation made by cooking whole, chopped, or pureed fruit and/or vegetables with added sugar until a thick texture is achieved.

It must contain at least 30% fruit and a sugar proportion between 40–59%.

Preserve

Unlike jam, preserves are made by cooking the pulp (or purée) of one or more types of fruit and/or vegetables with sugar.

They must contain at least 35% fruit in the final product and a sugar proportion greater than 60%.

Compote

Very similar to jam, as it is made by cooking whole or chopped fruit, but with a sugar content lower than 14%.

Jelly

Made by cooking the juice of one or more types of fruit, with a minimum sugar content of 35%.

Jam preserves

Today, the market offers a wide variety of jams, preserves, compotes, and jellies made from fruits and some vegetables, such as:

Strawberry
Apricot
Plum
Raspberry
Blueberries
Red berries
Orange
Chestnuts
Cherry
Apple
Mango
Pineapple
Tomato
Roasted peppers
Caramelized onion
Zucchini
Eggplant

These products are primarily composed of fruits and sugars but may also contain pectin, which can be natural (from the fruit itself) or added to help with gelling and achieving the right texture.

Additionally, additives like acidulants and preservatives are commonly included to ensure consistency, improve appearance, and maintain product quality. In some cases, colorants are added to enhance or improve the final color.

How to make jam preserves

Our first recommendation when making jam, preserves, compotes, or jellies is to ensure you have the necessary jars and lids, and check that none are broken or deformed.

Next, prepare the required fruits or vegetables. High-quality artisanal jams are typically made with seasonal fruit at its peak ripeness. Using locally sourced produce is also ideal, as it minimizes handling, reduces the risk of bruising, and is more sustainable.

These specific characteristics do not exclude less visually appealing produce. Jams are an excellent way to use fruits and vegetables that may not sell due to their appearance.

The selected fruits and vegetables should be carefully washed to remove any dust or soil. Depending on the type and variety, you may need to peel, pit, and deseed them.

Use a stainless steel knife to peel the produce to prevent the pulp from darkening.

To avoid oxidation, immediately immerse the peeled produce in cold water containing 10 grams of citric or tartaric acid per liter, or alternatively, acidulated water with lemon juice at a ratio of 15 tablespoons of juice per liter of water.

Then, proceed to obtain the pulp. This involves cooking the fruit to soften the skin and break down cellular tissues. This process unifies the pectin and makes the mass homogeneous, turning it into pulp.

During the cooking process, add the necessary ingredients.

Keep in mind that acid and pectin proportions vary depending on the type, variety, and even the ripeness of the fruit or vegetable used.

Another fun fact:

Did you know that the discovery of jam was closely linked to the discovery of different sweeteners? Honey was used first, followed by sugar cane, and later, beet sugar.

Sugar or sucrose is essential for the gelling and preservation of jam. The proportion of sugar relative to the total dry weight should not exceed 60%. If the sugar amount is too high, especially above 70%, there’s a risk that sugar crystals will form during cooling, affecting the uniformity and smoothness of the jam, making it less pleasant to the palate. To prevent this, we recommend adding sugar in stages and controlling the cooking temperature.
Many fruits lose their characteristic color during cooking, darkening or fading. If this happens, you can add a commercial organic colorant to create a more visually appealing product without introducing off-flavors or odors. The most commonly used colorants are red and green, as fruits with these colors tend to be the ones that most often lose their hue.

Once all ingredients are added and the mixture is cooked, allow it to cool.

Sterilization of jams

There are three key factors to consider when sterilizing jams, preserves, compotes, and jellies:

Cooking temperature
Acidity of the fruit or vegetable, which determines the pH
Water activity (Aw)

You’ve probably noticed that these products are typically stored on a shelf rather than in the refrigerator, indicating they have been pre-sterilized and can be kept at room temperature. This is because they have an acidic pH, allowing for low-temperature sterilization, below 100°C.

It’s worth noting that in some cases, if multiple preservation techniques are combined—such as reducing water content, increasing osmolarity, and adjusting pH—a pasteurization treatment may be sufficient to preserve the product.

While low-temperature sterilization below 100°C might be considered pasteurization, it is technically not. Due to the high acidity of these foods, low temperatures can effectively eliminate almost all microorganisms and bacteria, which is the outcome typical of sterilization.

Generally, sterilization involves higher temperatures, above 100°C, which allows for the elimination of nearly all microorganisms and provides the preserve with a longer shelf life without requiring refrigeration.

In contrast, pasteurization is less intense, as it is performed at lower temperatures. This means microorganisms are only partially eliminated, the product must always be refrigerated, and it typically has a shorter shelf life.

To market your jam preserves, confitures, compotes, and jellies, you must comply with food safety, quality, and hygiene regulations for canned foods and prepared dishes. This means it is mandatory to apply thermal treatment using professional equipment and to record the treatment results for each batch, as our TERRA Food-Tech^® autoclaves do.

pH of jams

The pH of a food is one of the factors that determines the temperature and time needed for thermal treatment, indicating which types of microorganisms can proliferate or be eradicated. A lower pH means higher acidity and a reduced risk of microbial growth, and vice versa.

Optimal pH values for preserved jams

The ideal pH range for jam to gel properly is between 2.8 and 3.5. This range, combined with thermal processing, ensures that the product can be safely stored at room temperature for extended periods, using low-temperature thermal treatment.

Fruit jams are generally quite acidic, so additional ingredients to lower the pH are usually unnecessary. However, if you need to reduce the pH, we recommend using small amounts of citric acid or lemon juice, which can adjust the pH without significantly affecting the flavor.

For vegetable-based jams (such as tomato, onion, pepper, etc.), these are often low-acid foods with a pH above 4.6. In these cases, pH alone is insufficient as a preservation method, as most microorganisms thrive in a near-neutral pH, between 5 and 8, especially between 6.5 and 7.5. Therefore, recipes of this type often incorporate citric acid or use higher-temperature thermal treatments.

F₀-P₀ values for jam sterilization

To sterilize jam preserves, you should typically set the temperature to around 80–90ºC, keeping in mind that higher temperatures can cause sugar caramelization. For this low-temperature sterilization, P₀ is generally applied, which typically ranges from 0.5 to 40, depending on the product’s pH.

These values are approximate, as F₀ and P₀ thermal values depend on the type of product, its ingredients, and how it was previously prepared. We recommend evaluating each product individually by accurately measuring its pH and conducting subsequent checks to assess the entire process, allowing you to select the most appropriate F₀-P₀ values for each recipe.

Common issues in jam sterilization

Although it is rare to find bacteria growing in jams due to the low water activity and high sugar concentration, which prevent bacterial growth, it is essential to avoid any risk by sterilizing. There is a type of bacteria that tolerates the osmotic pressure caused by high sugar concentration: osmophilic bacteria.

We must also be mindful of molds, which thrive in environments with high sugar concentrations.

Additionally, filling containers at a temperature below 85°C can lead to the growth of molds and yeasts on the surface.

Regarding organoleptic characteristics, prolonged heat exposure can cause:

Recommended containers for jam sterilization

Jams, preserves, compotes, and jellies are typically sold in glass jars, though single-serving portions are often packaged in small trays.

In addition to glass jars, other types of containers are increasingly used for these products. For example, compotes are also commonly found in small plastic trays or even pouches.

Glass jars are the most recommended for sterilizing jams. Glass is a translucent material that allows the contents to be seen, does not rust, and can withstand high temperatures. However, remember to leave some headspace between the jam and the lid when filling the jar.

A practical tip during the packaging process is to fill the containers while the jam is hot. This helps create a vacuum effect due to the product’s heat.

There are many types of containers available, and at TERRA Food-Tech^®, we provide insights into each to help you understand their advantages and disadvantages.

Sterilizing jams with TERRA Food-Tech^® autoclaves

TERRA Food-Tech^® autoclaves offer the ability to cook products before subjecting them to thermal treatments like pasteurization or sterilization. Thanks to the counterpressure they generate, they prevent container deformation. To avoid undesirable overcooking, these autoclaves ensure rapid cooling after the thermal treatment.

If you seek reliability, safety, and efficiency in producing gourmet preserves, a food autoclave is the ideal choice.

With TERRA Food-Tech^® autoclaves, you can not only sterilize but also cook and pasteurize—three functions in one device.

Our food autoclaves ensure compliance with safety, quality, and hygiene regulations for canned preserves and prepared dishes. They are essential for anyone looking to market these products.

TERRA Food-Tech® autoclaves were created to meet the needs of micro-entrepreneurs, chefs, cooks, farmers, livestock producers, and social organizations who have made gourmet preserve production their life’s work.

Canned jam success stories

Many of our clients produce fruit and/or vegetable jams in preserves. As we’ve mentioned, this is an excellent option for entrepreneurs. In our success stories section, you’ll find some of these clients and get to know their stories and experiences with our autoclave firsthand.

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