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One of the most crucial steps in developing a new food product is ensuring your product remains good until the end of its shelf life. It should remain safe and delicious to eat. You don’t want crusts that turn soggy, creams that turn hard, or fruit jams that develop molds.
Ideally, you want to tackle these problems early on in the development process. That way, it wouldn’t cause any delays, or worse, force you to recall products.
Often these shelf life challenges are due to the presence of too much, or too little moisture. But, if you know how much ‘available water’ your product contains, known as water activity, you can prevent many of these challenges.
We’ll discuss three shelf-life scenarios in which moisture matters.
Scenario 1: Preventing soggy fruit biscuits
We all intuitively know that a crispy cookie with a soft fruity filling might not remain crispy for long. The cookie often gets soggy, whereas the fruit filling might turn chewy. The same for a freshly made cream pie, we know the crust won’t remain crunchy for long. Within a day or two the crust will be soft.
Preventing water movement
This is all due to the movement of water. Water will always move through food products, from places where there’s a lot of available water, to places where there’s not as much. Water likes to distribute itself evenly. In our biscuits, water moves from the soft fruit filling to the crunchy cookie. In the pie, water moves from the filling to the crust.
If you do not want this water movement to happen, you have to ensure that the ‘water activity’ of both components is the same. Water activity is a measure of the amount of available water in a product. If the water activity of your crust and fruit filling are the same, water won’t move.
Luckily, it is very easy to measure the water activity of most foods. A simple water activity meter can determine the water activity within a few minutes, by simply placing a sample of the product in a measurement cup.
How to ensure equal water activity values
If the water activity of your two components is a long way apart you have to start changing your product. There are a lot of ways to do so. For instance, you can add more sugar to your fruity filling. Sugar binds water, and makes it less likely to move. Or, you can opt for modifying your cookie style to make it moister from the onset. Alternatively, you can add a barrier in between the fruity filling and the biscuit, to make it harder for the moisture to move.
There are many options, we’ve discussed several in detail in “Preventing Soggy Pie Crusts“. But, all rely on knowing the water activity of your components first, to strategically improve the product.
Scenario 2: Ensuring a long shelf life
Microorganisms can spoil our food, making it harmful or just unappetizing to eat. But, just like humans, microorganisms need water to grow and thrive. If there’s not enough water, they can’t grow. This provides food manufacturers with a great way for ensuring a long shelf of their products. Once the water activity of your product is below a certain threshold, it can be kept for a very long time, without any microorganisms growing on it.
Bacteria are most easy to stop this way. They stop growing at water activity values below approximately 0,87. Molds and yeasts need less water and won’t stop growing until values below 0,60. By again measuring the water activity of your product, you’ll know whether or not microorganisms can still grow, and if so, which.
By lowering water activity
To ensure microorganisms can’t grow, you’ll need to lower the water activity sufficiently. Again, there are several ways to do so. For one, you can decrease the amount of water, for instance by baking or frying a product. Or, you can add ingredients that hold on to water, ensuring that it is no longer available to use by microorganisms. Sugar is great at holding onto water and one of the reasons that a product like fruit jam contains a reasonable amount of sugar.
Scenario 3: Ensuring powders don’t clump
Milk powder, icing sugar, and wheat flour are all supposed to be soft free-flowing, smooth powders. However, if not stored correctly, they can start to form clumps. These clumps might not be a big issue if used by consumers at home. You can break them by hand, or simply work your way around them. But, in many larger-scale manufacturing facilities, clumped powders can wreak havoc. Powders may no longer flow through pipes, or get stuck in feeders.
Clumping of powders happens because the powders absorb water. The water causes the individual particles to stick together and form a clump.
Whether powders absorb moisture depends on the amount of moisture in the powder itself, the amount of moisture in the surrounding air and on the powder properties itself. Some powders are a lot more susceptible to becoming clumpy than others. Icing sugar and milk powder for instance are both more susceptible to forming clumps than wheat flour is.
In this instance, you again will want to know more about the water activity of your product. But, in this instance, the analysis is slightly more complicated. You’ll want to know the relationship between the amount of water in the air and the amount of water in your product. You can do so by making an isotherm. It’s a slightly more advanced method, again based on water activity.
Once you know under which conditions your powder starts to clump, you can start preventing it from happening. You might need to adjust your packaging, or the storage conditions. Or, you might need to add an anti-clumping agent (which you’ll often see added to icing sugar).
Why Moisture Matters
Powders that clump during storage. Pie crusts or cookies that turn soggy during shelf life. Or products that spoil too fast. They’re all caused by the unwanted presence of water. You can predict if and how it might happen by measuring the water activity of your products.
Once you have those crucial values, you can act. Adjust your storage conditions, change packaging, tweak recipes, or adjust production processes to ensure your products remain good during shelf life. A relatively simple analysis can prevent you from having to delay a new product launch, or recall products.
Knowing what to analyze and when, can help you develop better, safer products. Water activity specifically is a key metric to keep an eye on when developing products. If you are struggling with the shelf life of your products, and think water might be key:
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