Solving Moisture Issues in Snack Foods

Rancidity, moisture migration, texture changes, mold – snack foods are susceptible to a range of possible complications. Watch Mary Galloway teach how to prevent them. 

Achieving the perfect taste or texture is only the beginning – from then on, your customers expect perfect consistency, year after year.

In this brief webinar, we explored the issues that can cause unexpected problems in snack foods, how manufacturers can avoid getting blindsided, and surefire methods for delivering consistency. In this webinar, you’ll learn:

  • Why predicting lipid oxidation can be counterintuitive
  • How moisture migration can cause unpleasant surprises
  • How to reliably predict texture changes
  • Efficient ways to reformulate snacks for more market appeal


Mary Galloway is the application scientist for AQUALAB and manages the Food Research & Development lab. She is a contributing author on several publications concerning water activity and its influence on physical properties. Mary uses her years of experience to help customers understand and solve their moisture-related product issues.

Webinar Transcript

Mary Galloway, presenter: Good morning. Thank you for joining us. Today we’ll discuss snack foods and how to manage moisture.

Intro: The top three moisture issues in snack foods

I’ll present on the top three snack food pitfalls: rancidity (lipid oxidation), texture changes and moisture migration within the product. Then we’re going to talk about how we can use this information for product formulation and how to achieve consistency in your products.

Snack food is a very diverse group of products. We have chips, crackers, candies, meat products, and healthy things that have a nutritional value. They’re ready to eat, they tend to be in the low to intermediate moisture area, and they’re packaged to easily consume. We want the consumers to just tear into them — that’s what makes them a snack food.

Generally snack food brands are striving for a specific customer experience — when you eat a chip or a cracker you want a nice crunch, and if you’re eating beef jerky, you want a very different texture.

Most brands are not worried about mold issues because they live in a lower water activity range. The water activity range for mold is 0.7 and most snack foods are below that. So how can water activity be useful if we’re not talking about mold?

Well, the question is, what happens when problems arise?

What if you make a trail mix that now has rancid nuts? Or a bar that has gotten hard, or started molding before expiration? That one’s been a fairly hot topic in the media lately. And what about a filled cake with unappealing sticky moisture inside the package?

Can we foresee these problems and figure out how to avoid them? And can we use this to help with new formulations?

Total moisture measurements are key to solving problems

Moisture content is needed for the right texture, that’s what’s going to help deliver a good customer experience. When they eat the cracker, chip, or beef jerky I mentioned before, it’s the texture that they’re looking for.

That’s why we need to know moisture content. However, moisture content isn’t going to help when we have moisture related issues — what we really need is a total moisture measurement, which is moisture content related to water activity.

Water activity is the key to figuring out these crucial moisture related problems, not moisture content. I’ll go into that a little more in the future.

So I have some snack foods here. We’re going to focus on the three main issues in snack foods that I mentioned before — lipid oxidation (rancidity), changes in texture (going soft, going hard, or both), and moisture migration within multicomponent products.

Issue #1 – Lipid oxidation

So for lipid oxidation, foods that have an issue with this are foods that have a high fat content. Generally we’re talking about chips, nuts, fried items, cheese, seeds, those kinds of things. But it’s not just the high fat content, it’s this other part — low moisture content and a low water activity.

Let me explain why that’s a problem.

This is a stability diagram. What’s really useful and interesting here is the lipid oxidation curve. This is showing water activity across the x axis, that increases from left to right. Then the moisture content and relative reaction rate is on the y axis there.

If we follow the trajectory of the lipid oxidation, we’ll see that it starts really high at low water activity levels, then swings down. The reaction rate is actually reducing until we hit about 0.325. Then it surges back up as the water activity increases after that point. So as we’re looking at this, keep those high fat snack products I mentioned in mind.

Take a potato chip for example — the water activity for a potato chip is around 0.1 – 0.2. If you look at that range on the graph here, you’ll see it has a very high lipid oxidation rate in this zone here. But we also notice that it plateaus, and is at its very lowest between 0.3 and 0.5 water activity. What that means is that if we can move the water activity up to 0.3 – 0.5, that reduces that risk of lipid oxidation to the very lowest rate.

The reason for that is that in the lower water activity area on the left, fat molecules are exposed to the air, so the air is doing the oxidation at that point. Then we hit the lowest lipid oxidation rate, the water actually envelops the fat molecule and protects it. Then as we increase water activity again, the oxygen in the water itself becomes a reactant and starts oxidizing the fat. So if you can bump up the water activity of your product to between 0.3 and 0.5, you’ll no longer have an issue with liquid oxidation.

The real problem here is that you’ll lose crispness in that area — but for these products, that’s what the consumer wants, right? They want a nice snap of a chip. So how do we overcome that? By balancing the texture with the possibility of rancidity.

So oxygen is our enemy, honestly. That’s what’s going to cause rancidity. What can we do to reduce it? Well, use an oxygen absorber — and you’ll see that in some of these products. Or you can introduce a nitrogen flush or another environment flush, that’ll displace the oxygen in there. Basically, if you reduce the oxygen in the package, then you don’t have as much oxygen to react with the fat and cause rancidity.

The other thing is to pick the right packaging. This diagram explains water vapor transmission rate, or how much water comes into the package. You want to make sure you maintain the right kind of packaging. So the lower the vapor transmission rate, the better — it’s more sealed against the water in the air.

Another thing you need to look at is the OTR, the oxygen transmission rate. You’ll want that to be low as well, because if your package has a really good water vapor transmission rate, but has a high OTR, you’re still letting a lot of oxygen in, and that’s going to cause rancidity.

The other consideration is that light has a huge effect on the oxidation reaction. If you can minimize light in the package, you’ll be a lot better off. So no clear packaging, and no packaging with windows. Even if you have amazing packaging all around, but add a little window to see the product, that can be a real weak spot.

Issue #2 – Changes in texture

These are slightly different because we’re not talking about foods that have high fat content. Some of these are vegetable crisps, dried fruit, cookies, crackers, bars, some confections, gummies, licorice maybe, and some functional ingredients. These products have low to mid range moisture content and the same for water activity.

What can cause a loss of texture for these products? We’re looking here at a diagram of the atmosphere and how packaging prevents moisture coming through. That’s your greatest enemy here — the environment surrounding your product, or exterior conditions.

If you have packaging that’s wax paper lined or something like it, it won’t have a very good water vapor transmission rate – it’ll be too high, a lot of water and vapor will be able to get into or out of your product.

Because moisture can actually go both ways. We’ve had customers who, let’s say, make a bar that gets hard over time, and they’re trying to figure out how that can happen. It’s because the packaging isn’t really protecting it from exterior conditions.

If we have a higher humidity in the atmosphere outside, moisture can get through the packaging and increase moisture levels inside the product – but it can go the other way too. If your product is higher in moisture than the atmosphere, then it goes the other direction, so you can lose moisture through the packaging.

Another thing to consider is the storage conditions. Temperature and relative humidity are going to affect that as well. If you have a high temperature or high humidity storage condition, say in a truck, that will affect the moisture content and water activity of the product, depending on on how well they’re insulated with the packaging.

Generally, in 99% of cases, an increase in temperature will increase your water activity. If you produce a product and you’re very happy with – good water activity, good texture, everything wonderful, but the packaging isn’t as great – if you put it in a high temperature area, the water activity increases. And if it increases to the point where your product is undesirable, then you have a problem.

So I want to give a quick example of some kale chips that we’ve tested in the past. This is an isotherm. I’m gonna interject a little bit – I showed a little bit of one in the stability slide. If you’re not familiar with isotherms, I do talk about them a fair amount. We have really great resources on our website about isotherms, how they’re useful and what you can do with them. I recommend you go to the website and look for it. You’ll find some really good information.

So back on this isotherm – we’ve taken kale chips and put a sample on our instrument, put over moist air for the adsorption. And then we track the weight, and then we dry it down. That shows us how the product reacts in the presence of moisture or, or in a drying condition. We can tell a lot from this, especially when we’re talking about texture.

I have a little circle right here that says RHc, which means critical water activity or relative humidity. Because we’re talking about the air, it’s at 0.57, which means that for the kale chips, this point signifies a change in the texture. This is the point where the kale chips start to go soft. And that’s not what the manufacturer wants, he wants them nice and crisp.

This tells us that if we keep the chips below 0.57 water activity, then we maintain the crisp texture that we’re looking for, and still stay below the 0.7 water activity for mold.

Issue #3 – Moisture migration

All right, moisture migration. This is slightly different from texture changes caused by external factors entering the product. Here we’re talking about moisture migration within two or more of the components.
The products that have this issue are things like filled cookies, cakes, bars with inclusions or cookies with inclusions. So fruits, nuts, chocolate, fruit nut mixtures. I’ve had manufacturers talk about how they’ll put a fruit or nut together, then get some problems, and they don’t understand why.

Why does moisture move? It doesn’t have to do with moisture content at all. It has to do with physics and energy levels. And when we talk about that, we’re talking about water activity.

So in this chart, we’ve got blueberries here on the left at 0.66 water activity, and we’re going to add them to these almonds on the right that have a 0.43 water activity. What’s going to happen? Well, when you put these things together, the moisture is going to move because the water activity levels don’t match. In this case, the water is going to move from the blueberries to the almonds.

So how do you manage that? You’ve got to put these ingredients together, you’ve got to build your product, so how can you manage the moisture migration? This chart shows one example: You can actually predict what the final water activity will be after you mix them. You’d predict the final water activity level those blueberries and almonds together will end up at – and if you’ll have problems.

Here’s another example I have of a super simple cold press bar. We’ve got date paste as the blue trace here. Then we’ve added some cashews – they’re very flat, they’re very dense, so they don’t pick up moisture very well. And then we also have coconut that we decided to throw into the mix.

These are the isotherms for each one of those components. This chart comes from a program we have here at AQUALAB. It’s predicted that the water activity with all these together is at this blue line right here. That’s a calibration point. And then the combined isotherm between these two products is here in purple. It says that when we mix all of these together, the water activity is going to be 0.63.

Now we go back and assess – is that okay? Well, the cashews are going to, have the biggest effect from this, meaning that they’re going to increase in moisture. But maybe that’s all right, maybe the texture is still low, right? Maybe in this bar, it’s acceptable.

So to reiterate, you pick your ingredients, you predict the final water activity, and then you assess for each of those components. In this case, maybe it’s fine, and we can move along. And if it’s not fine, you can make adjustments, but you can do this before you mix anything at all.

Another way you can do it is to come at it from a different angle. Pick a common water activity, then adjust each of your components’ water activity to match.

So I use this example kind of a lot – this is a snack cake that’s filled, and then iced. It has three different components, and they all have completely different textures. That means they have three very different moisture contents. Here are the isotherms. You’ll see here that the icing is in blue, there’s a lot of sugar, obviously, in the icing, and that tends to be very flat. We have a lot of fat in the cream filling, here’s the isotherm for that. And then we have the cake in green.

In this case, we’ve decided the water activity needs to be 0.7. At 0.7, all of these are going to have the right texture. The cake isn’t going to be too hard or too soft. The cream filling will be nice and creamy, and the icing is going to do a good job of protecting the cake as the moisture barrier.

But notice that they all maintain the same water activity even though they have very different moisture content. So here, the cake is at 20% moisture content, the cream filling is around 15%, then the icing is around 5%.

So that’s another way we can come about it – pick a specific water activity where we like all of our individual components, then put them all together. Because they’re all the same water activity, no moisture is going to move.

All right, so what if those methods aren’t available to manage moisture migration? Well, you can slow the diffusion process, but eventually that moisture is going to move. Maybe you can slow it down enough that it’ll maintain its shelf life for the time period that you want. Like I said, it’s still going to happen, but maybe you can slow it down so you still can achieve your desired shelf life.

The other idea is you can actually create a physical moisture barrier. Take as an example, chocolate. If you’ve ever had a pre-packaged ice cream cone, you’ve seen that they coat the inside of the cone with chocolate, and that’s the moisture barrier between the ice cream and the actual cone itself.

If you can’t do any of the above, you can do separate packaging. Think cheese and crackers – even shelf stable cheese and crackers. The cracker needs to be crisp, the cheese needs to be soft, and sometimes you just can’t make that happen. But you can just completely separate them in their packaging.

Using total moisture for easier product formulation

All right, how do we use this information for formulation? Let’s say we’ve got products that we know are in the lipid oxidation trouble area, or the change in texture, or the moisture migration trouble area. Then we know what our biggest enemy is, and we can be aware of these and avoid them.

How do we do that? Let’s say we want to come up with a new variety or new flavor of something. You can use that previous information and transfer it to your new variety.

Or say you’re interested in doing a clean label reformulation, so it has no preservatives, or maybe you’re reducing sugar or whatever. How do we take that into account? Well, we now know how ingredient changes affect the final product, so we can characterize new formulations.

Here’s a quick graphic I have here with water activity and moisture content, like we’ve been seeing on the isotherms. We have two different formulations. This could be two different bars, or a coating on a gummy so we don’t have the syneresis that happens with gummies sometimes where they get sticky on the outside. So we’re trying new coatings. Well, you could run isotherms on those, then compare how moisture interacts between them.

You can also relate the degradation of functional ingredients to water activity, which is really fantastic, because then you can take all this key information like moisture content, water activity, potency of your functional ingredient – vitamin C or a protein or whatever it is – and combine them and have all of it in one chart, all correlated, so you can produce the optimum formulation.

All right. So those are great, tell us what we’re getting into, show where pitfalls are, and help plan how we’re going to combat them.

Using total moisture to ensure product consistency

How do you consistently get the results? Now you know where you want to go, but how are you going to get there? What we need to be doing is producing with consistency.

In this graphic, in the center I have this adorable little smiley face. That’s where we want our customers to be, right? We want them to have brand loyalty because we’ve been producing consistency. They’ll know when they get your package that it’s exactly what they’re expecting, no nasty surprises, no mold or rancid nuts or anything like that. If we can achieve that, then the consumer is going to be inclined to try new products that we come out with, right? They had good experiences with product A and B, so when we come out with products C and D, they think, “Oh, I really liked those other ones, I’m willing to try this new one and see if I like it too.”

Unfortunately, that can go the other way too. Negative experiences will impact future perceptions as well. Let’s say we did have a product that they liked, but then the bar started going moldy, and they had a whole box they had to throw away. That’s going to make them very hesitant to buy your product in the future or try any changes you might want to introduce to them. So you’ve got to be aware of both of these – you need to focus on producing consistency.

So here’s a little graphic. This is a sample isotherm – let’s continue with the bar example. We have here in the red, a target water activity we’re shooting for. It also shows a certain moisture content we want that gives just the right texture. If we can maintain this zone here, we are going to hit that sweet spot. The beautiful thing about hitting the sweet spot, is that it’s going to give the consumer what they want every time.

It’s going to minimize some negative things and increase positive things. Let’s say we’re in this zone here, where we’re dropping water activity and lower moisture content, here we lose quality. That’s not what the consumer wants. When we go too high, we’re losing safety. We want to build in a buffer. If we have a product that’s going to be in a high temperature area, we know that’s going to increase its water activity, and that might change the texture or introduce mold conditions. Then in this area here, with a lower moisture content, we’re losing out on yield and revenue. You’re drying your product too much, it’s not in the optimal zone.

Generally these things are sold by weight, so you know that’s going to hurt the business. So if you can hit that sweet spot right here, that will help in every conceivable way, both the business and the product.


How can you use total moisture? Total moisture is when we’re talking about moisture content and water activity. Both of those need to be monitored because you want to make sure you’re maintaining the right texture. And you want to make sure the water activity is right so you don’t have any surprise issues with moisture migration or texture change or the other things we’ve already talked about.

So you can use this measurement to set process specifics to say, “Okay, that’s the sweet spot I want, this is what we’re going to do,” then monitor it. You can know if there will be changes in your production. Say your oven is running too hot – you’ll see that if you’re monitoring moisture content and water activity, and you can make an adjustment. You can do it before it gets to the end of the line, QA final testing, where you’d find out “Oh, we’ve missed the mark here.” You can make those adjustments in production early on. Then you know that if you’re always hitting those specifications, you’re going to get a reliable product, no surprises. You’ve already done all the pre-formulation. You’re using all the information you can.

Key points in review

So here are some of the key points I want to stress.

  1. With lipid oxidation, you’ve got to remember that you need to balance the texture and the oxidation level. You might have to get a little more creative, think a little differently, about how you’re going to combat that.
  2. You want to be able to manage the moisture within a product. You need to know the water activity and how it’s going to move.
  3. You can pre-formulate with key data, tie all that moisture information from all your individual components together, even predict degradation of your nutritional additives.
  4. You can use total moisture readings after you’ve formulated to figure out all these other factors that’ll help you produce a consistent batch every time.

Alright, that’s all for my presentation today. Thank you for attending!

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