Why can a jar of jam sit on a shelf before it is opened while fresh strawberries need refrigeration? Why can dried apricots last for months, even though they still contain water? And why does adding sugar, salt, or vinegar make such a dramatic difference in how long certain foods last?
The answer is more nuanced than simply asking how much water a food contains.
The key concept is water activity, usually written as aw. Water activity measures how much water in a food is available for microorganisms and chemical reactions. It is different from total moisture content, and that distinction explains a huge part of the science behind shelf-stable foods.
So, what is water activity food preservation? In simple terms, it is the use of water activity to control the amount of water available for microbial growth and spoilage. When water is bound tightly by ingredients such as sugar or salt, microorganisms have less access to it, even though the food may still contain a substantial amount of moisture.
That is why foods such as jam, dried fruit, cured foods, and some pickled products can have a surprisingly long shelf life.
Understanding water activity gives you a better way to think about food preservation. Instead of viewing water as simply “present” or “absent,” food science asks a more useful question:
How available is that water?
What Is Water Activity in Food?
Water activity is a measure of the availability of water in a food for biological and chemical processes.
It is represented by aw and is expressed on a scale from 0 to 1. Pure water has an aw of 1.00. Foods have lower values because their water interacts with sugars, salts, proteins, starches, acids, and other components.
A useful simplified definition is:
Water activity is a measure of how much water is available to microorganisms and other processes in a food.
This is important because microorganisms do not simply need “water” in the general sense. They need access to water that they can use.
Two foods can have similar moisture contents but very different water activities.
That difference is one of the most important ideas in understanding shelf stable food science.
Water Activity vs. Moisture Content
Moisture content tells you how much water is physically present in a food.
Water activity tells you how available that water is.
Those measurements are related, but they are not interchangeable.
Imagine two foods that each contain 30% water. If one food has ingredients that strongly bind much of that water, its water activity may be significantly lower than the other food.
The first food could therefore be less hospitable to microbial growth despite containing the same total amount of water.
This is why simply drying a food until it “feels dry” is not a complete explanation of preservation. Likewise, measuring moisture alone doesn't tell you everything about whether a food can support microbial growth.
Why Does Available Water Matter?
Microorganisms such as bacteria, yeasts, and molds require available water to grow.
If water activity becomes low enough, microbial growth becomes increasingly difficult or stops altogether.
Different microorganisms have different minimum water activity requirements. Many common bacteria need relatively high water activity, while some yeasts and molds can tolerate considerably drier conditions.
This creates an important food-preservation strategy:
Lower the water activity enough to make the food less favorable to the microorganisms that could spoil it or make it unsafe.
That can be accomplished in several ways, including:
- Removing water through drying
- Adding sugar
- Adding salt
- Combining ingredients that bind water
- Using preservation methods that work alongside reduced water activity
Water activity is therefore not just a laboratory measurement. It helps explain why traditional food preservation methods work.
How Does Water Activity Prevent Food Spoilage?
Water activity affects whether microorganisms can grow.
When available water is plentiful, microorganisms have an environment in which they can reproduce. As water activity decreases, that environment becomes less favorable.
At sufficiently low water activity, many microorganisms cannot grow.
The important point is that lower water activity does not necessarily mean a food contains no water.
A raisin is an obvious example.
A raisin is not completely dry. It contains water, but much of the original water has been removed, and the remaining water is also influenced by the food's high concentration of sugars and other dissolved substances.
The result is a much lower water activity than you would find in fresh grapes.
Water Activity and Microbial Growth
Water activity influences the growth of:
- Bacteria
- Yeasts
- Molds
Bacteria generally require more available water than many yeasts and molds. This is one reason drying and concentration can be especially effective against bacterial growth.
However, lowering water activity does not automatically make every food indefinitely safe.
Some microorganisms are remarkably tolerant of dry or high-sugar environments. Certain yeasts and molds, for example, can survive and grow at water activities that prevent many bacteria from growing.
That's why shelf stability often depends on multiple preservation factors, not just one.
What Is the Difference Between Water Activity and Moisture Content?
The difference between moisture content and water activity can be explained in one sentence:
Moisture content measures the total amount of water in food, while water activity measures the availability of that water.
This distinction is critical.
A food can have relatively high moisture content while having lower water activity if much of its water is bound or otherwise unavailable.
Conversely, a food can have a lower moisture content but still contain enough available water to support certain microorganisms.
Think of moisture content as asking:
“How much water is there?”
Water activity asks:
“How accessible is that water?”
For food preservation, the second question is often much more useful.
A Simple Everyday Analogy
Imagine a swimming pool.
If the pool is completely accessible, people can easily get into the water.
Now imagine that much of the water has been locked inside sealed containers around the pool. The total amount of water might still be substantial, but there is less water available for people to use.
Food ingredients can have a somewhat analogous effect on water.
Sugar, salt, and other dissolved substances interact with water and reduce its availability. The water hasn't necessarily disappeared. It has simply become less available for certain biological processes.
That is the basic idea behind water activity aw explained in practical terms.
Why Jam Doesn't Usually Need Refrigeration Before Opening
Jam provides one of the clearest examples of water activity in food preservation.
Fruit naturally contains water. If you simply leave fresh fruit at room temperature, microorganisms can eventually grow, and the fruit deteriorates.
Jam is different.
Traditional jam combines fruit with a significant amount of sugar and is typically heated during processing. The sugar reduces water activity by binding water and lowering the amount available for microbial growth.
The heat treatment also plays an important role by reducing microorganisms present during processing.
The result is a food environment that is substantially less favorable to many spoilage organisms than fresh fruit.
Sugar Isn't Just for Sweetness
When people think about jam, sugar usually brings sweetness to mind.
From a food-science perspective, sugar has another important role.
Dissolved sugar interacts with water. As the concentration of dissolved sugar increases, water activity generally decreases.
This is why high-sugar foods have historically been used as preservation methods.
The same general principle applies to products such as:
- Fruit preserves
- Jellies
- Marmalades
- Fruit spreads
- Syrups
- Candied fruit
The exact shelf life and safety of a product depend on its formulation, processing, packaging, acidity, water activity, and storage conditions.
So it would be inaccurate to say that “sugar preserves everything.” Instead, sugar is one important tool for controlling the food environment.
Why Dried Fruit Lasts So Much Longer Than Fresh Fruit
The science behind dried fruit preservation is especially easy to understand once water activity is clear.
Fresh fruit contains a large amount of water. That moisture supports the texture and metabolic activity of the fruit, while also creating conditions that can support microbial growth.
Drying removes a substantial portion of that water.
As water is removed, the concentration of remaining sugars, acids, minerals, and other components increases. The water activity falls.
That's why raisins, dried apricots, dates, prunes, and other dried fruits can have much longer shelf lives than their fresh counterparts.
Drying Does More Than Make Food Smaller
It is tempting to think of dehydration as simply removing water until a food becomes dry.
But the preservation effect is more specific.
Drying changes the food's internal environment.
As water leaves:
- Total moisture decreases.
- Solutes become more concentrated.
- Water becomes less available.
- Microbial growth becomes more difficult.
- The food generally becomes more shelf-stable.
The degree of drying matters. A food that is only partially dried may still have enough available water to support some microorganisms.
This is why commercially produced dried foods are formulated and processed to meet specific preservation targets rather than simply being dried until they look different.
Why Salt Preserves Food
Salt works on a similar principle.
When salt is added to food, it dissolves into the food's water phase. This changes the environment and reduces water activity.
Historically, salting was one of the most important methods of preserving foods before modern refrigeration.
Salted foods include many traditional products such as:
- Salt-cured vegetables
- Brined foods
- Salted fish
- Cured meats
- Some fermented foods
Salt preservation is not simply about making food salty. The concentration of salt, amount of moisture, acidity, temperature, processing conditions, and other factors all matter.
Salt also creates conditions that selectively affect microorganisms, meaning the overall preservation process can be more complicated than water activity alone.
How Pickles Stay Shelf-Stable
Pickles introduce another important concept: multiple hurdles.
Many pickled foods use an acidic environment, salt, heat processing, and sometimes reduced water activity. These factors work together to make microbial growth more difficult.
Vinegar contributes acidity. Salt can lower water activity. Heat processing can reduce microorganisms. Packaging can prevent contamination after processing.
This is an example of what's sometimes called a hurdle approach to food preservation.
Instead of relying on one barrier, food scientists can combine several barriers.
For example:
Acidity + salt + heat processing + appropriate packaging = a much less favorable environment for microbial growth.
This is one reason it is misleading to explain shelf stability using a single ingredient.
Does Vinegar Lower Water Activity?
Vinegar's primary preservation role is associated with acidity rather than being treated as a simple water-activity control.
Acidification can make a food less favorable to certain pathogens and spoilage organisms. Salt and sugar, meanwhile, can directly contribute to reducing water activity.
In a real food product, these factors can overlap.
That's why the preservation science of pickles involves more than simply asking whether vinegar is present.
What Water Activity Numbers Mean
Water activity ranges from 0 to 1.00.
A value close to 1 means water is highly available. A lower value means less water is available.
For example:
- Pure water: aw = 1.00
- Fresh, high-moisture foods: generally high aw
- Intermediate-moisture foods: lower aw
- Very dry foods: often much lower aw
The exact water activity of a food depends on its formulation and processing.
A useful food-science rule of thumb is that many common bacteria struggle as water activity drops below about 0.90, although specific organisms have different requirements.
A major food-safety threshold often discussed is aw 0.85, because lowering water activity below this level can significantly limit the growth of many pathogenic bacteria. But that does not mean a food below 0.85 is automatically shelf-stable or free from all microbial hazards.
Some yeasts and molds can tolerate substantially lower water activity.
For this reason, food manufacturers measure aw rather than relying on appearance or a simple moisture measurement.
Why Low Water Activity Doesn't Mean "No Spoilage"
One of the most important misconceptions about water activity is that low aw makes food immune to spoilage.
It doesn't.
Lower water activity can prevent or slow the growth of many microorganisms, but it does not stop every possible deterioration mechanism.
Foods can still experience:
- Mold growth
- Yeast growth
- Oxidation
- Flavor changes
- Color changes
- Texture changes
- Enzymatic reactions
- Chemical degradation
Water activity affects many of these processes, but not all of them in the same way.
A shelf-stable food can therefore remain safe from certain types of microbial growth while still losing quality over time.
Can Mold Grow in Low-Water-Activity Foods?
Yes.
This is a particularly important distinction.
Molds and certain yeasts can tolerate lower water activity than many bacteria. That's one reason a food can be relatively resistant to bacterial growth while still being vulnerable to mold under certain conditions.
Consider dried fruit.
Drying reduces water activity and significantly extends shelf life. But if dried fruit absorbs moisture from humid air, its water activity can rise.
That can change its susceptibility to spoilage.
This is why packaging matters so much for dehydrated foods.
Humidity Can Change Water Activity
A food doesn't exist in isolation.
It interacts with its environment.
If a dried food is exposed to humid air, it can absorb moisture. As its moisture content rises, its water activity may rise as well.
This creates a practical food-storage lesson:
A food that is shelf-stable when properly packaged may become less stable after absorbing moisture.
That is why resealable packaging, moisture barriers, and appropriate storage conditions matter for dried foods.
Opening a package repeatedly can expose the contents to humid air. Over time, the food can change even if it originally had a very long shelf life.
Why Refrigeration Still Matters
If water activity is so important, why do we refrigerate so many foods?
Because refrigeration and water activity solve different problems.
Refrigeration slows microbial growth and many chemical reactions by lowering temperature.
Water-activity control changes the availability of water.
Food preservation can use either strategy or combine them.
Fresh milk, for example, has plenty of available water, so refrigeration is important. Dry cereal has much less available water and can remain shelf-stable under appropriate conditions.
Some foods use both approaches.
A refrigerated food might have moderately reduced water activity but still require cold storage because its aw remains high enough to support certain microorganisms.
Water Activity and Temperature Work Together
Microbial growth depends on more than one variable.
Important factors include:
- Water activity
- Temperature
- Acidity or pH
- Oxygen availability
- Nutrient availability
- Competing microorganisms
- Preservatives
- Processing history
This means the same water activity can behave differently under different storage conditions.
A food's preservation system is therefore best understood as an interaction among several variables.
The "Hurdle Technology" Behind Shelf-Stable Foods
Food scientists often think about preservation as a series of hurdles.
Each hurdle makes it more difficult for undesirable microorganisms to survive or multiply.
Common hurdles include:
Low Water Activity
Drying, sugar, and salt can reduce available water.
Low pH
Acidic conditions can inhibit many microorganisms and are particularly important in controlling certain foodborne pathogens.
Heat
Cooking or commercial heat processing can reduce microbial populations.
Refrigeration
Lower temperatures slow the growth of many microorganisms.
Preservatives
Certain ingredients can inhibit specific microorganisms or chemical reactions.
Packaging
Packaging protects food from oxygen, moisture, light, and new sources of contamination.
A shelf-stable product may rely on several of these hurdles simultaneously.
That is why food preservation cannot always be reduced to a single ingredient or number.
How Food Scientists Measure Water Activity
Water activity isn't normally determined by simply squeezing a food or measuring its water percentage.
It is measured using specialized instruments called water activity meters.
A sample is placed in a sealed measurement chamber. The instrument evaluates the equilibrium relative humidity associated with the sample and uses that information to determine its water activity.
The concept is related to vapor pressure.
In simplified terms:
aw = vapor pressure of water in the food ÷ vapor pressure of pure water at the same temperature
This relationship explains why water activity is not the same as moisture content.
Two foods can contain the same amount of water but have different vapor pressures because their ingredients interact with that water differently.
Why Temperature Matters When Measuring aw
Water activity measurements are temperature-dependent.
As temperature changes, the behavior of water and the vapor pressure associated with it can change.
That means accurate measurement requires controlled conditions.
For commercial food production, water activity measurement can be part of quality control and product-development processes.
It can help manufacturers verify that a formulation reaches the intended level of microbial stability.
Water Activity Is Especially Important in Product Development
Suppose a food company wants to create a shelf-stable snack.
It could begin with ingredients that contain water and then adjust the formula using drying, sugar, salt, acids, or other components.
Rather than guessing whether the final product will remain stable, food scientists can measure its water activity.
That measurement can help answer questions such as:
- Can bacteria grow in the product?
- Could yeast become a problem?
- Is the formulation dry enough?
- Will moisture migration affect stability?
- Does the packaging provide enough moisture protection?
- Will the product remain stable throughout its expected shelf life?
This makes water activity an important quality-control tool as well as a theoretical food-science concept.
Moisture Migration: A Hidden Shelf-Life Problem
Water activity becomes even more interesting when a food contains different components.
Think about a snack made with a moist fruit filling and a dry outer layer.
If the two components have different water activities, moisture can migrate from one part of the food to another.
Over time, the filling may become drier while the outer layer becomes softer.
This can affect:
- Texture
- Crispness
- Stability
- Microbial growth
- Consumer quality
The food may still contain approximately the same total amount of water, but the distribution of that water has changed.
This is one reason food formulation and packaging are closely connected.
Why Packaging Matters for Shelf-Stable Food
Water activity describes the food's internal environment, but packaging helps maintain that environment.
A dried product may have low water activity when manufactured. If its package allows significant moisture transmission, the product can gradually absorb water from the surrounding atmosphere.
That can raise water activity and shorten shelf life.
Good packaging can therefore act as a moisture barrier.
For shelf-stable foods, manufacturers may consider:
- Water vapor transmission
- Oxygen transmission
- Seal integrity
- Light exposure
- Storage temperature
- Humidity
- Package size and headspace
The goal is not merely to make a food stable once. The goal is to keep its preservation characteristics stable throughout its intended shelf life.
Is Water Activity the Same as Dryness?
No.
A food can feel dry without having extremely low water activity.
Likewise, a food can feel moist while having a lower water activity than you might expect because its ingredients bind water.
Texture is useful as a sensory clue, but it isn't a substitute for measuring water activity.
This is particularly important when developing homemade shelf-stable foods.
A recipe that produces a product that “looks dry enough” isn't necessarily a scientifically validated preservation process.
Can You Tell Water Activity by Looking at Food?
Not reliably.
You cannot determine a food's exact water activity simply by looking at it, touching it, or tasting it.
Appearance can provide clues about moisture, but water activity depends on how water interacts with the entire food matrix.
For example, two foods could both appear moist but have very different water activities.
If shelf stability or food safety depends on a specific aw level, measurement is the reliable approach.
Common Foods Explained Through Water Activity
Let's look at several familiar foods through the lens of water activity.
Fresh Fruit
Fresh fruit typically has high moisture content and high water activity.
That makes it perishable and susceptible to microbial growth.
Refrigeration can slow deterioration, but fresh fruit generally does not become shelf-stable simply because it has natural sugars.
Raisins
Raisins start as high-moisture grapes.
Drying removes much of their water, while their natural sugars become more concentrated.
Their lower water activity makes them substantially more shelf-stable than fresh grapes.
Jam
Jam combines fruit with significant amounts of sugar.
The sugar reduces water activity, while heat processing and acidity may provide additional preservation hurdles.
Honey
Honey is a classic example of a food with high sugar concentration and relatively low water activity.
Its concentrated sugars make water less available to microorganisms.
However, honey can absorb moisture from its environment, so storage conditions still matter.
Salted Foods
Salt can reduce water activity by interacting with water in the food.
Traditional salting and brining methods use this principle to create less favorable conditions for microbial growth.
Crackers
Crackers and other dry baked foods have relatively low moisture and low water activity.
Their main shelf-life challenges may involve moisture absorption, oxidation, and quality loss rather than the same microbial growth concerns associated with fresh foods.
Does Freezing Lower Water Activity?
Freezing and water-activity control are related but not identical.
When food freezes, some water becomes ice and is no longer available in the liquid phase for microbial activity.
However, frozen food should not be thought of simply as a food with “low water activity.”
Freezing works primarily by lowering temperature and changing the physical state of water.
When food thaws, the preservation conditions change again.
This is another example of why food preservation is best understood as a combination of environmental factors.
Why Some Foods Still Need Refrigeration After Opening
A shelf-stable food can have a very different preservation environment once its container is opened.
Consider a commercially processed jar of jam.
Before opening, the sealed container protects the product from environmental contamination and helps preserve its intended conditions.
After opening, the food is exposed to:
- Air
- Moisture
- Spores
- Yeasts
- Bacteria
- Repeated temperature changes
- Utensils and other sources of contamination
Even if the product's water activity remains relatively low, new organisms may be introduced.
That's why package instructions matter.
A product that is shelf-stable unopened may still need refrigeration after opening.
Water Activity and Food Safety Are Not the Same Thing
Water activity is an important food-safety parameter, but it is not a complete safety test.
A particular aw value can tell you a great deal about the potential for microbial growth. It does not automatically tell you whether a food is safe under every condition.
Other factors matter, including pH, processing, packaging, storage temperature, contamination, and the microorganisms involved.
This distinction is especially important for homemade preserved foods.
If you're trying to make a shelf-stable product at home, don't assume that reducing moisture or adding sugar automatically creates a safe preservation method.
Validated recipes and established food-preservation procedures are much safer guides than intuition.
How to Lower Water Activity in Food
There are several broad food-preservation strategies that can reduce water activity.
1. Dehydration
Removing water through controlled drying is one of the most direct methods.
Examples include:
- Dried fruit
- Jerky
- Dried vegetables
- Powdered ingredients
- Dried herbs
The challenge is reaching and maintaining the desired level of dryness.
2. Adding Sugar
Sugar reduces water activity by interacting with water.
This is especially important in products such as:
- Jam
- Jelly
- Preserves
- Candied fruit
The concentration matters. A small amount of sugar is not equivalent to the high sugar concentration found in a traditional preserve.
3. Adding Salt
Salt lowers water activity and has been used for centuries in preservation.
The amount and distribution of salt matter, as do the other properties of the food.
4. Concentrating Food
Evaporation can remove water while leaving sugars, salts, acids, and other solids behind.
This concentrates the food and typically lowers its water activity.
Fruit preserves and concentrated sauces can use this general principle.
5. Combining Preservation Hurdles
In many foods, water activity is just one part of a larger preservation strategy.
A product may combine reduced aw with acidity, heat treatment, preservatives, refrigeration, or protective packaging.
This combination can provide stronger control than any single method.
Practical Tips for Understanding Shelf-Stable Foods
When evaluating whether a food is shelf-stable, don't ask only whether it contains water.
Ask these questions instead:
Is the food commercially processed?
Commercially produced shelf-stable foods are generally formulated and processed with specific safety and quality targets.
Is the container sealed?
An unopened sealed package provides a very different environment from an opened container.
Is the food acidic?
Acidity can significantly influence which microorganisms can grow.
Is the food dried or concentrated?
Drying and concentration can reduce available water.
Is sugar or salt present at meaningful concentrations?
Sugar and salt can lower water activity, but the concentration matters.
Has the food absorbed moisture?
Dry foods can become less stable if they take up moisture from humid air.
What does the package say?
For commercially prepared foods, storage instructions should take priority over general rules.
A Quick Rule for Water Activity
If you remember only one concept from this article, make it this:
Food preservation is not simply about removing water. It is about controlling the water that microorganisms can actually use.
That's the heart of what is water activity food preservation.
A fresh grape and a raisin both contain water. But the raisin has much less available water because drying and its concentrated sugars create a different environment.
Jam contains water, too. But its high concentration of dissolved sugar reduces water activity and works alongside other preservation hurdles.
Pickles may combine acidity, salt, heat processing, and packaging.
Different foods reach shelf stability through different combinations of barriers.
Water Activity and Plant-Based Foods
Water activity is relevant across the entire food system, including plant-based foods.
Many plant foods are naturally high in moisture and therefore highly perishable when fresh. Drying, concentration, fermentation, acidification, freezing, and other preservation methods can extend their usability.
Understanding the science can also make everyday food choices more intuitive.
A dried fruit snack isn't shelf-stable because it somehow contains “no water.” It has a preservation advantage because its available water is much lower than that of fresh fruit.
For people interested in plant-based living, food preservation can be a practical way to reduce waste and make better use of seasonal produce. That interest can extend beyond the kitchen into everyday lifestyle choices, including supporting businesses such as The Dharma Store, which connects plant-based living with mindfulness, compassion, and ethical choices. For a wearable expression of that outlook, its Vegan T-Shirts collection reflects the same plant-focused message.
What Water Activity Teaches Us About Food Preservation
The biggest lesson from water activity is that food science often depends on what we cannot see.
A food may look wet but have relatively little water available to microorganisms.
Another food may look dry but still have enough available water for certain organisms to grow.
The difference comes from the interaction between water and everything else in the food.
Sugar, salt, proteins, starches, acids, temperature, and packaging can all influence the food's preservation environment.
That is why moisture content vs. water activity is such an important distinction.
Moisture tells you the quantity.
Water activity tells you something about the availability.
For predicting microbial growth, that availability can be the more meaningful measurement.
Frequently Asked Questions About Water Activity
What is water activity in food preservation?
Water activity is a measure of how much water in a food is available for microorganisms and other biological or chemical processes. It is represented as aw on a scale from 0 to 1.00. Lower water activity generally makes it harder for microorganisms to grow.
What is the difference between water activity and moisture content?
Moisture content measures the total amount of water in a food. Water activity measures how available that water is. Two foods can have similar moisture contents but different water activities because their ingredients interact with water differently.
What water activity prevents bacterial growth?
Many bacteria have difficulty growing as water activity decreases, with a commonly referenced threshold around aw 0.90 for many bacterial species. An aw below 0.85 significantly limits the growth of many pathogenic bacteria, but it does not mean every microorganism is unable to grow. Some yeasts and molds can tolerate lower water activity.
Why does dried fruit last longer than fresh fruit?
Drying removes water and lowers water activity. The remaining water is less available for microbial growth, while naturally occurring sugars and other solids become more concentrated. This makes dried fruit much more resistant to many forms of microbial spoilage than fresh fruit.
Does sugar reduce water activity?
Yes. Dissolved sugar interacts with water and reduces its availability. This is one reason high-sugar foods such as traditional jams, jellies, and preserves can have long shelf lives when properly formulated and processed.
Does low water activity make food shelf-stable?
Not necessarily by itself. Low water activity can inhibit many microorganisms, but shelf stability can also depend on acidity, heat processing, packaging, preservatives, temperature, and other factors. A food should not be assumed to be safely shelf-stable based only on how dry or sugary it seems.
The Takeaway: Available Water Is the Key
The next time you see a shelf full of jam, dried fruit, or another food that doesn't require refrigeration, think beyond moisture.
Those foods haven't necessarily been made completely free of water.
Instead, food scientists have changed the environment so that much less of the remaining water is available for microbial growth.
That's the central idea behind water activity.
Water activity measures the availability of water, not simply the amount of water.
Drying lowers available water. Sugar can bind water and lower its activity. Salt can do the same. Acidification, heat, packaging, and refrigeration can add additional preservation barriers.
Together, these principles explain a surprising amount of everyday food preservation.
Once you understand water activity, the shelf life of a raisin, the stability of jam, and the preservation of many traditional foods stop looking mysterious. They're examples of food science built around one deceptively simple question:
How much of the water is actually available?
The information in this article is for educational purposes only and should not be considered medical advice. Always consult a qualified healthcare professional regarding dietary or health concerns.