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Pickles and jams

Here is Why Pickles and Jams Don’t Spoil Easily: A Simplified Food Science Perspective

Pickles, jams, and jellies are some of the few foods that have been surprising consumers with their ability to stay for long periods without spoiling, given their moist nature.

Just like honey (which doesn’t have an expiry date), pickles and jams possess special structural and biological properties that make them resistant to spoilage microbiological and physical conditions.

Before I go further into exploring these special properties, let’s first bring everyone to speed with some definitions.

What Are Pickles?

Pickles are basically fruits, vegetables, or meats that have been preserved in either a brine solution (a solution containing table salt), vinegar, or other acidic preservatives.

In the US and most parts of the world, pickles are usually associated with canned or jar-packed cucumbers.

Pickling is however not just a cucumber thing and can be done on a wide variety of foods such as the ones I have mentioned above.

The history of pickling dates back to thousands of years before human civilization.

This is one of the few creative techniques used by ancient people to preserve their foods for future use.

Today, pickling is not only a food preservation method but also serves as a way of improving the quality of the preserved food.

You can find a variety of pickled products at your local supermarket shelves or online stores over the internet.

What Are Jams and Jellies?


Jams and jellies are part of a group of foods known as condiments in food science and technology.

This simply means they are supplementary foods used with other main foods to give them a better taste.

These products are edible gels that are neither liquid nor solid and are usually used for spreading on bread and sandwiches.

Jams and jellies are typically made from a mixture of crushed fruit pulps cooked with sugar and a gelling aid compound known as pectin to a semi-solid consistency gel.

I will give a more detailed description of the science of gelling so that we can appreciate how the process contributes to their long shelf life.

Just like the pickles, jams and jellies are also ancient preservation methods used by fruit lovers to make seasonal fruits available even during their off-season.

Why Are Pickles and Jams Not Easily Spoiled by Bacteria?

To understand this question, let’s revisit how these foods are made and packaged.

Their production process and the ingredients used to make them are actually the reasons why they will not spoil faster.

In summary, the reason why pickles and jams are not easily affected by food spoilage microorganisms is due to the highly concentrated salt and sugar solutions synonymous with these products that inhibit growth of spoilage bacteria and fungi.

Due to the hypertonic nature of pickles and jams, all the water that is necessary for living organisms to thrive is bound and inaccessible to spoilage microorganisms in the products.

How Are Pickles Made?

The process of making pickles is fairly simple and straight forward.

  • To make a pickle, you will need a brine solution or a solution of an edible organic acid such as acetic acid or citric acid.
  • You also need the fruit or vegetable to be pickled. This can either be whole or sliced.
  • It is recommended to blanch (partially cook and cool) the product to kill enzymes that cause spoilage.
  • The product is then immersed into the chosen boiled solution in a jar and some other optional ingredients such as seasonings, colorants, garlic, spices, and stabilizers are added.
  • The jar is then tightly sealed and left to pickle over time.

Why Pickles Don’t Spoil Faster

The process that goes on inside the jar to produce the final pickled product is known as lacto-fermentation.

This is simply a process where lactic acid microorganisms find the brine environment favorable and thus convert natural sugars in the picked product into lactic acid.

The lactic acid drastically reduces the pH of the pickle juice (makes it more acidic) to a level that is unfavorable to most food spoilage microorganisms.

As you can see here, the bacteria are fighting in two battlefronts; the acidic environment and the salty environment.

The acidic environment is obviously prohibiting for any living organism to thrive.

The salty environment on the other hand creates a hypertonic solution that draws away water from the bacteria cells through the process of osmosis rendering them hopeless on that battlefront.

Since they are single-celled organisms, their cells will be denatured by plasmolysis as a result of losing water.

This makes pickles able to sit on the shelves for more than two years without spoiling.

How are Jams and Jellies Made?

The process of making jams and jellies is more complex and involving than the pickling process.

This is why you will not find many people preparing them at home.

To get the required consistency and quality, you will need some precise measurement of ingredients and following of the recipes to the latter.

It is however not impossible to do it at home. Many sites on the internet have simple recipes that you can follow to make your own jam or jelly at home.

The process essentially follows these steps:

  • You need to have the ingredients which include; ripe high pectin fruit (preferably citrus fruit), pectin, and normal sugar (sucrose).
  • The process begins by extracting the required fruit juice by squeezing and simmering while constantly stirring.
  • The other ingredients; pectin and sugar are added respectively and boiled while constantly stirring until a gel is formed. The setting temperature is usually around 220oF and can be measured using a food thermometer.
  • The product is then filled hot into sterilized jars or cans.

To get a full recipe of making jams and jellies, I would recommend this source here.

For now, let’s keep it at what makes these gels stay that longer on the shelves.

Why Jams and Jellies Have Longer Shelf Lives.

As you can see in this basic recipe, there is sugar which is a basic ingredient in jam and jelly making.

The amount of sugar required for the product to gel is usually more than 50% of the ingredients used.

Similar to salt, sugar also makes the food environment unfavorable to bacteria.

In this case, the sugar will act by denying the food spoilage microorganisms water, which is an essential factor for growth and survival.

Sugar achieves this by reducing what food scientists technically call a product’s water activity or simply denoted as (aw).

Let me deconstruct this jargon a little here.

aw and Food Spoilage

You see, in food science, it has been proven that almost everything on earth including a dry piece of wood or a concrete stone contain some amount of water.

These waters cannot be measured by the normal moisture levels used to determine the amount of water in a product.

The water can be present in a substance but bound so that it is inaccessible to microorganisms.

Water activity thus helps us to know how much water is unbound and available to microorganisms.

According to scientific research, the values of water activity are usually between 0 and 1, whereby 0 means there is no aw (no available water) and 1 means the water is available for bacterial growth.

Most spoilage microorganisms will not grow below 0.90 aw whereas no single known microorganism can grow below 0.60 aw.

Unlike other foods, jams and jellies have an aw of 0.8. This means that the water is not accessible to spoilage bacteria.

Note I have specified bacteria here because molds are an exception to this rule as we shall see later here.  

For this reason, the gel structure in jams and jellies denies most spoilage microorganisms the water they really need to survive.

This means the products can stay for extended periods of time without going bad.

How Long Can Pickles and Jams Stay Fresh?

So, how long is long when it comes to the shelf life of these products?

The shelf lives for pickles and jams are considered long because of the physical nature of the products in comparison to other similar products such as fresh vegetables or juices.

In general, pickles can stay for up to 2 years in sealed cans or jars while jams and jellies have an average shelf life of 1 year when opened and refrigerated.

You can check more of these and other food products shelf lives here.

This, however, doesn’t mean that you can carelessly handle these products and expect them to last that long.

As seen earlier in my previous article here, the shelf life will still depend on how well you follow the manufacturer’s storage instructions.

Why Would Pickles and Jams Spoil?

As much as these foods have a reputation of staying longer on the shelves, nothing actually lasts forever. Not even our own planet.

This means that you should expect spoilage after some time.

The reason for this is partially what I mentioned at the water activity section about molds.

Molds can be quite stubborn.

Most of them can grow at lower water activity levels of below 0.7aw.

With jams and jellies having a 0.8aw, it means the molds can still have a party on our jams and jellies if left exposed.

That is why it is recommended you refrigerate it after opening for longer shelf life.

Pickles on the other hand can also spoil before the two-year window.

The reason for this is the existence of some salt-loving bacteria called halophiles that can survive very high salt concentrations.

You therefore need to ensure that you do not let them inside your pickled products by following manufacturer’s usage instructions.

If you are making them at home, you need to store them in the refrigerator and away from other contaminants.

Read Also: What is Temperature Danger Zone of Food: Find Out Why Food Spoil Faster in Summer

How Can You Tell if Pickles and Jams Have Gone Bad?

After reading all this, you might be wondering how you can tell a bad pickle or jam from a good one.

There are the common metrics of physically examining the product for color changes, container bulges, bubbles, or changes in consistency.

There are also other organoleptic tests such as bad odor, slimy texture, or unpleasant taste from the product.

The easiest and most ignored way is to simply look at the date markings which give the expiry dates.

It is important to keep these small checks in mind because these products especially those made at home can cause severe instances of botulism if not canned or jarred correctly.

With this information, I hope you can enjoy your pickles and jams with peace of mind.

6 thoughts on “Here is Why Pickles and Jams Don’t Spoil Easily: A Simplified Food Science Perspective”

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  5. Hello Dan,
    I find the article very OK.

    With the following points captured, it’s on point.

    Hypertonic nature of pickles and jams makes water inaccessible to spoilage microorganisms in the products.

    Blanching kills enzymes that cause spoilage.

    Microorganisms having to fight acidic environment and the salty environment.

    Jam making process

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