Moisture Challenges in the Food Industry: Basics & Beyond

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04/02/2025 Added

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Moisture Challenges in the Food Industry: Basics & Beyond by Zachary Cartwright, AQUALAB by Addium. 2025 High Pressure Processing and Dehydration Workshop

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[00:00:00.000]Hi, everyone. My name is Zach Cartwright, and the title of my presentation today is
[00:00:09.600]Moisture Challenges in the Food Industry, Basics and Beyond. I was hoping to give this
[00:00:14.960]in person last week at the University of Nebraska. Unfortunately, due to the snowstorm, I got
[00:00:20.460]stuck in Minneapolis and wasn't going to make it there for a few days. So I'm going to go
[00:00:25.600]ahead and record this presentation. It is an abridged version. It's a little shorter.
[00:00:30.420]Originally, I planned on for about an hour, but I know that you might not want to sit
[00:00:35.300]here on your computer or on your phone for that long. So a little bit of a shorter version
[00:00:39.900]today, but if you have any questions afterward, my contact information will be at the end
[00:00:44.900]and I hope that you reach out to me. I will also send these slides over, so don't worry
[00:00:50.640]about remembering everything or writing things down. We can make sure that you get a
[00:00:55.580]copy of these slides. Now, the reason that I'm focusing on water today is because water is really
[00:01:01.980]such a critical factor in the food industry and other industries as well, like cosmetics and
[00:01:07.420]pharmaceuticals and even things like cannabis. But basically, when water isn't controlled, this is
[00:01:13.680]when we start to have problems with physical changes. You can think of caking and clumping of
[00:01:19.040]powders, or maybe you're losing the ideal texture of a certain snack food. Maybe there's an ideal
[00:01:25.560]crispness or a texture that your consumers are expecting. And if water isn't kept in check,
[00:01:32.120]then the physical structure will change, and it can really affect the organoleptic qualities
[00:01:38.540]or the flowability or whatever that physical trait is. If we don't control water,
[00:01:44.820]we can also have chemical changes or chemical reactions that take off. This can be things like
[00:01:50.520]lipid oxidation, which we'll talk about today, or maybe browning reactions or
[00:01:55.540]maybe the degradation of certain vitamins or active components. So water activity is directly
[00:02:02.820]related to the rate that reactions take off. And finally, when we don't keep water in check,
[00:02:09.240]if there's too much water there, if it's available, then things can start to grow.
[00:02:14.000]So you might have yeast or bacteria or different types of molds that will start to grow and cause
[00:02:20.480]spoilage or even get people sick. And so water is connected.
[00:02:25.520]To all of these different safety and quality attributes that we're trying to control
[00:02:30.640]within foods and overcoming moisture challenges.
[00:02:34.680]It really requires measuring, controlling and even understanding water at each and every
[00:02:42.340]step of the production process. So whether you're working really early on
[00:02:46.920]in research and development, or maybe you're in product development,
[00:02:50.780]and you're trying to think about how moisture is going to affect safety,
[00:02:55.500]and quality parameters of that product over its lifespan. Or maybe you work in sensory analysis,
[00:03:01.520]and you're trying to understand how different amounts of water is going to affect different
[00:03:06.380]organoleptic qualities. Maybe you're somebody who works on ingredients, and you need to
[00:03:11.520]understand how to validate incoming ingredients and set the right specs to make sure that any
[00:03:18.460]variation isn't going to be carried into production and cause trouble where you might be trying to hit
[00:03:25.480]a specific moisture spec or water activity spec. Production is where we see a lot of waste in the
[00:03:31.560]food industry, especially if you're using any type of heating process where you're trying to hit and
[00:03:37.320]reduce the amount of variation as it relates to moisture. So maybe you're somebody in production.
[00:03:45.400]Maybe you work in quality assurance and quality control, and you need to understand what water
[00:03:50.680]activity meter that you need or what moisture analyzer, or maybe you don't quite understand
[00:03:55.460]the difference between these parameters. Water is really important as it comes to packaging,
[00:04:01.540]especially if you're looking at different water vapor transmission rates for different types of
[00:04:06.500]packaging to preserve products. And finally, when it comes to shelf life, keep in mind that water
[00:04:12.660]activity is dynamic. It changes over time, and we can use this to really understand and even predict
[00:04:19.860]the shelf life of different products very quickly without having to wait months for accelerated
[00:04:25.440]testing or maybe years for full shelf life testing. So really to control moisture, it is a
[00:04:30.960]start to finish process, and you have to be able to measure, control, and understand the water at
[00:04:37.660]each of these steps, and we'll get into that just a little bit today. Overall, the goals of my
[00:04:44.220]presentation is I want you to be able to walk away today having a better understanding of water
[00:04:49.900]activity. I want you to know how water activity is different from moisture content and
[00:04:55.420]how each of these measurements, they do have their uses, but depending on where you are in
[00:05:01.340]that last figure from start to finish, depending where you are, you may want to use one or the
[00:05:07.100]other or maybe a combination of both. Today, we're going to talk about how water activity
[00:05:12.300]impacts microbial growth. We'll look at how water activity also affects lipid oxidation. This has
[00:05:19.240]been a really common thing that's come up recently in my discussions, so I decided to include a
[00:05:25.400]few slides. We'll talk a little bit about moisture sorption isotherms. These are used as an R&D tool,
[00:05:31.980]and even though we won't get into every application today, if you're an R&D scientist
[00:05:36.580]or a product developer and you have follow-up questions, once I get to those slides, please
[00:05:42.400]reach out and we can go more in depth. We'll talk about some of the R&D challenges that isotherms
[00:05:49.340]solve, and finally, we'll look a little bit into how variation can be reduced.
[00:05:55.380]Let's start off with water activity. It's often defined as unbound or free water. It's water that
[00:06:05.160]may be available for different chemical reactions, different physical changes, or maybe it's there to
[00:06:11.520]support microbial growth. One of my favorite examples, a really great way to think about this
[00:06:17.840]is if you collect all of the water molecules in whatever sample or product that you're making,
[00:06:23.720]and if we have a sponge,
[00:06:25.360]let's say that this sponge represents the physical structure of the product that you're working on,
[00:06:31.240]and if we take the sponge and put it into this glass of water, then it's going to soak up and
[00:06:37.360]bind a certain amount of the water, and there will be also a certain amount that's left over,
[00:06:42.640]and this remaining water represents the water activity. It's water that's available for chemical,
[00:06:49.360]physical, and biological changes. Now if we were to put this sponge in here, and let's
[00:06:55.340]say that it binds up all of the water and there's no water left, in this case we have
[00:07:00.620]a water activity of zero. There's nothing available for these types of changes that
[00:07:06.020]we've been discussing. But really a better way to define water activity is that it's
[00:07:12.160]actually energy. It's a form of energy. It's a principle of thermodynamics, and in thermodynamics
[00:07:19.180]we learn that energy is a driving force, and in this case it's a driving force
[00:07:25.320]for those microbial, chemical, and physical changes. And the other thing that we learn in
[00:07:31.040]thermodynamics, if you remember, is that energy always wants to be at a lower state. Energy always
[00:07:38.240]wants to move from high to low, and the same is true for water activity. Water activity always
[00:07:43.800]wants to move from high to low, and so this is really helpful when formulating new products
[00:07:49.820]where we're trying to prevent moisture migration, because if we can formulate
[00:07:55.300]different components or different products to the same water activity, then no moisture
[00:08:00.440]migration is going to occur between those different components or those different products.
[00:08:06.620]Three major things are going to affect water activity. It's primarily affected by chemical
[00:08:12.420]and physical bonding, so if the water is bound up either physically or maybe chemically by a
[00:08:25.280]humectant that you've added, then when that water is bound up, it's no longer available
[00:08:30.340]and the water activity is going to decrease. The second thing that will affect water activity is
[00:08:36.800]the amount of water that's there. If there's less available, if the moisture content goes down,
[00:08:43.040]then there's not as much water that can be used for different processes or different reactions,
[00:08:48.760]so the water activity is going to decrease. And then finally, temperature is also going to
[00:08:55.260]really affect water activity. Generally, as temperature increases, the water activity
[00:09:00.580]is also going to increase. And if we go back and again, thinking about this in terms of
[00:09:06.480]thermodynamics, temperature is a form of energy, and if we're adding energy to that system,
[00:09:11.720]then the water activity is going to go up as well. There's a few exceptions to this rule,
[00:09:17.540]things like oils or other cases, you may see a little bit of an inverse effect,
[00:09:22.100]but most of the things that you're probably working on,
[00:09:25.240]especially in the food industry, you're going to see the water activity increase
[00:09:29.100]as the temperature also increases. This next slide is just about the available
[00:09:35.220]technologies for water activity, just so that you're aware of what's out there and what you're
[00:09:41.520]paying for. There's basically four different sensors that you'll come across. This is basically
[00:09:48.240]what you're paying for, the type of sensor in a water activity device. There's a chilled mirror
[00:09:55.220]sensor, a tunable diode laser or a TDL sensor, capacitance sensors, and resistive electrolytic
[00:10:03.600]sensors. So all of these are different approaches to measuring water activity.
[00:10:07.580]The two on the left, the dew point and the TDL, these are considered primary direct methods for
[00:10:15.040]measuring water activity, while the second set of sensors, the capacitance and the resistive
[00:10:25.200]electrical properties and electrical changes, and then correlating that to define a water activity.
[00:10:32.260]The two methods on the left, these are going to take much less time, one to four minutes or three
[00:10:39.080]to seven minutes, you'll see there for the TDL. These other two can take quite a long time,
[00:10:44.500]especially if you're waiting for a full length sample and waiting for equilibrium to occur.
[00:10:50.520]These can take a very long time. And this is something to definitely be aware of,
[00:10:55.180]if you are a producer or a quality lab that has to run through a lot of samples.
[00:11:00.960]The accuracy of all of these devices, honestly, or all of these sensors is pretty good. You'll
[00:11:07.000]see slight changes here. But these days, these all do pretty well if you're taking a full length
[00:11:13.120]reading. Next, I have the lifespan dewpoint sensor. I talked to people using these types
[00:11:19.540]of sensors from the 90s or even earlier. This sensor lasts a really long time. And
[00:11:25.160]if you take good care of it. The TDO, this is a laser method. It basically lasts forever. I
[00:11:32.940]think that as long as it's maintained, there's no reason that this should really ever stop working.
[00:11:39.260]These other ones, again, that rely on electrical properties, after a few years,
[00:11:44.440]you're going to start to see drift and you're going to lose some accuracy. Temperature, again,
[00:11:50.560]is really important when measuring water activity. We want to make sure that we're always measuring
[00:11:55.140]at the same temperature so that we're not adding any extra noise to the data that we're collecting.
[00:12:00.640]And you'll see here that some of these units are temperature controlled and others are not.
[00:12:05.660]And finally, some instruments are able to measure samples that contain volatiles. So things like
[00:12:13.140]ethanol or propylene glycol or certain spices. And so if you're working on products that contain
[00:12:19.500]high amounts of volatiles, then you really need to use this TDL KIPP
[00:12:25.120]PASATEN sensors are able to handle some amounts of volatiles or they're able to use filters on
[00:12:31.500]them that you have to change out. But just be aware that if volatiles are in your sample,
[00:12:36.420]then you need to make sure that you're using the right type of sensor.
[00:12:40.620]The next few slides that I want to focus on really look at water activity versus moisture
[00:12:47.460]content. So moisture content is an amount and it's a quantitative measure of water. So again, if we
[00:12:55.100]take every molecule of water out of something and collect that, this represents the moisture
[00:13:00.840]content. And it's generally expressed as a percent on a wet basis. So zero to 100%. I know
[00:13:08.880]other industries, things like soils, you may see this on a dry basis and you may see numbers that
[00:13:14.520]wouldn't really make sense for what we use in the food industry. Moisture content is primarily used
[00:13:21.000]for things like yield and calculating revenue, maybe
[00:13:25.080]looking at different ingredient concentrations and also for different
[00:13:29.820]labeling requirements. So moisture content definitely has its place and a
[00:13:35.160]lot of production teams are really going to focus on moisture content because
[00:13:39.760]water is the cheapest ingredient in any formulation. I say
[00:13:44.860]this all the time and production teams definitely have that type of
[00:13:49.140]mindset so they usually are going to talk in terms of moisture content.
[00:13:55.060]There are a few different methods that we can use for moisture. There are primary
[00:13:59.560]methods and secondary just like water activity. The primary methods that you'll
[00:14:04.300]usually see are loss on drying methods. These are things like using an oven or a
[00:14:08.940]vacuum oven. You put your sample in there for a very specific time at a specific
[00:14:14.520]temperature and then using this calculation here on a wet basis you'll
[00:14:19.240]get a percentage or maybe you'll see a Carl Fischer titration setup. It may look
[00:14:25.040]something like this and this is basically using a specific chemical
[00:14:29.100]reaction that I have here and looking at how much of a reactant is consumed and
[00:14:36.040]using that to calculate the moisture content. Then there are also secondary
[00:14:40.800]methods. Things like moisture balances are typically pretty common. Moisture
[00:14:45.840]balances are difficult because they often use a halogen bulb and quickly
[00:14:51.160]burn the sample and you're removing things other than water.
[00:14:55.020]These generally don't tend to be a very precise way and have a lot of
[00:15:01.080]variation. Then there are other methods as well: NIR, dielectric, and so on.
[00:15:06.420]There may be other methods, but usually these have to be calibrated. Just
[00:15:10.660]like the secondary methods of water activity, they're not directly measuring
[00:15:15.440]moisture here. They're just using some type of electrical change or some type
[00:15:20.020]of change that has to be constantly calibrated in order to
[00:15:25.000]give you an idea of where the moisture content is. Some of the major difficulties
[00:15:30.040]with moisture content is that most of these methods are going to have a really
[00:15:34.480]high degree of variation, maybe plus or minus one percent at their best, and keep
[00:15:41.400]in mind that the accuracy of any moisture method is really unknown. We
[00:15:46.180]can't talk in terms of accuracy when it comes to moisture. We don't know when
[00:15:51.620]we've removed or accounted for every molecule
[00:15:54.980]of water in that sample or in that product and this means that when it
[00:15:59.240]comes to moisture we can really only focus on precision and repeatability. So
[00:16:04.880]we don't know how close we are to the accuracy but we do get an idea of how
[00:16:09.620]repeatable or how precise the methods are. Also keep in mind that every method
[00:16:16.340]that you use for moisture content is going to give you a different result and
[00:16:21.140]this makes it really hard if you're comparing data from different public
[00:16:24.960]locations or you're comparing data from one lab or one location to another. You
[00:16:30.000]really want to make sure that you're on the same page, that you're using the same
[00:16:33.600]method and this can also really lead to misleading labeling.
[00:16:39.900]One really good example is in the cannabis industry because THC
[00:16:45.080]content is calculated based on the moisture and if I'm a cannabis producer
[00:16:51.780]and I really want it to look like my bud has really
[00:16:54.940]high THC then I'm going to shop around and I'm going to pick
[00:16:59.520]the testing lab that uses a moisture method
[00:17:02.800]that is going to give me basically the result
[00:17:06.260]that I want. So if you have this presentation if you
[00:17:10.620]click here on this marijuana leaf it will take you actually to a
[00:17:14.480]publication or a short article where I discuss that a little bit more.
[00:17:19.060]Overall I thought it would be helpful just to compare water. I
[00:17:24.920]and moisture content here in a table. So water activity is a
[00:17:28.620]form of energy. Moisture content is an amount. Water activity is
[00:17:33.440]qualitative and even though we get a value for water activity
[00:17:37.100]why I say that is because we can directly connect water activity
[00:17:41.200]to the safety and the quality of the products you're working on.
[00:17:44.980]Moisture content is quantitative. It's mainly used to calculate
[00:17:49.600]yield and revenue. Water activity is a driving force. Moisture
[00:17:54.900]content is just an amount. It's not really a driving force. For
[00:17:58.740]water activity, we have known standards. These are different
[00:18:02.300]salt solutions that we can make that have known water activities.
[00:18:06.560]This allows us to verify the calibration of any water activity
[00:18:10.840]meter. Moisture content is just an empirical measurement.
[00:18:14.820]There's nothing that has an inherent moisture content that we can
[00:18:18.880]compare to, so we don't know the accuracy. And finally,
[00:18:22.960]water activity is unitless.
[00:18:24.880]It ranges from zero, something with no, water activity up to one,
[00:18:29.080]the same water activity as pure water. Moisture content is a percent
[00:18:34.340]on a wet basis in the food industry from zero to 100%.
[00:18:39.800]Next, I love including this example. I use it all the time,
[00:18:45.000]but I think it really helps us to see how things can have very
[00:18:48.820]similar water activities, but drastically different moisture
[00:18:52.400]contents. So if you were to think about this,
[00:18:54.860]which of these has the higher moisture content? I'm always
[00:18:59.440]surprised it's usually split, maybe 50-50. But keep in mind
[00:19:03.620]that honey is in liquid form, so it has to have a higher
[00:19:07.900]moisture content. And then which of these has a higher water
[00:19:12.680]activity? And you may think that it's the honey because the
[00:19:16.800]moisture content is drastically higher. But in this example,
[00:19:20.740]the water activity is actually the same for these two.
[00:19:24.840]And if you were to take those cookies and put them in the
[00:19:28.560]honey, how long would it take for the cookie to start to
[00:19:32.420]become soggy? And if these are truly at 0.6 water activity for
[00:19:37.320]both of them, then no moisture migration is going to occur and
[00:19:41.560]those cookies will retain the texture that we're after.
[00:19:45.420]Next, I wanted to talk about preventing microbial growth. So
[00:19:51.260]keep in mind that microorganisms, of course, they need water
[00:19:54.820]in order to grow. And if that microorganism is surrounded in
[00:19:59.560]an environment by a lower water activity than the inside of the
[00:20:04.180]microorganism, like in this example, we're at 0.95 on the
[00:20:08.460]inside of this imaginary microbe, and let's say it's 0.9
[00:20:12.880]on the outside, then that cell, that microorganism is going to
[00:20:17.440]have a lot of osmotic stress, and moisture migration is going
[00:20:21.720]to start to occur. So water is going to move from the
[00:20:24.800]interior to the exterior, and it's going to have a loss of
[00:20:29.300]turgor pressure. Okay, so this cell or this microorganism is
[00:20:33.340]going to be really stressed out. And in order to compensate for
[00:20:37.960]this, the microorganism can start to lower its own water
[00:20:42.360]activity by switching some of its metabolic processes. So it
[00:20:46.880]might start to bring in amino acids and polyols and sugars and
[00:20:50.740]different things. It might also change the structure of
[00:20:54.780]the cell membrane in order to bring these different things in.
[00:20:59.000]And if that microorganism can reduce its water activity to
[00:21:03.900]match the environment, so let's say that it can come down to
[00:21:08.180]0.9 water activity, then it's able to grow and reproduce. So
[00:21:12.800]there's no problem here. It's able to adapt to the
[00:21:15.840]environment. But let's say that it tries to adapt. It changes
[00:21:19.700]those metabolic processes, but it's only able to get down to
[00:21:24.760]0.92 in this example. If the microorganism can't match the
[00:21:30.640]environment, then it's going to go dormant. And this is great
[00:21:35.100]for us as food producers, especially if you work in food
[00:21:38.600]safety, because we can use water activity to control what's able
[00:21:43.200]to grow. So keep in mind that this is not a kill step, but it
[00:21:47.820]is a control step. So we can make something safe, but not
[00:21:54.740]on the water activity and its ability to prevent microbial
[00:21:58.560]growth. This next slide is just a table of different well-known
[00:22:04.940]published limits for different microorganisms. I just want you
[00:22:09.600]to notice, I guess these are all pathogenic microorganisms, and I
[00:22:13.720]just want you to notice here that Staphylococcus aureus is at
[00:22:17.300]0.86, and this is why some products legally have to be
[00:22:21.960]below 0.85 water activity.
[00:22:24.720]Because no pathogenic bacteria is able to grow.
[00:22:28.820]Keep in mind that water activity is just one of many hurdles that
[00:22:33.720]we can use as food producers or people in the food industry in
[00:22:37.660]order to prevent a microorganism from growing.
[00:22:41.500]We can also use things like heating or refrigeration, or
[00:22:44.900]maybe you're using acid, or you're limiting the amount of
[00:22:48.380]oxygen, and so on.
[00:22:50.020]And so this is from one of my favorite figures, where it
[00:22:54.700]just shows that you can use different strategies or
[00:22:57.220]different combinations of these hurdles to prevent
[00:23:00.520]microbial growth.
[00:23:01.560]This is often what I see with products that I work with.
[00:23:05.640]Maybe there is some type of heating step that's being used,
[00:23:09.720]and then water activity is the second major hurdle.
[00:23:12.840]Or maybe water activity is the secondary hurdle, and then pH
[00:23:18.380]is that tertiary hurdle, really preventing things to grow.
[00:23:21.840]So depending on your product that you're working on,
[00:23:24.680]or maybe even a different formulation of the same product,
[00:23:27.440]you might need to use a different combination of these different hurdles,
[00:23:31.220]and maybe one of them is water activity.
[00:23:34.180]So just keep that in mind.
[00:23:35.760]It's just one of the tools in our toolbox to prevent microbial growth.
[00:23:41.040]Next, I wanted to talk a little bit about reducing lipid oxidation.
[00:23:46.300]Like I mentioned earlier at the start, this has come up a lot recently
[00:23:50.960]and in some of my own discussions, but keep in mind that
[00:23:54.660]lipid oxidation is really going to occur when we have unsaturated fatty acids
[00:24:00.140]and they're reacting with oxygen and this forms lipid hydroxychloroquine.
[00:24:05.160]hydroperoxide. So it looks something like this, where we have our fatty acid and oxygen is getting
[00:24:10.820]into the system, maybe due to the packaging, or maybe it's already present, or maybe it's
[00:24:16.920]actually in the water that's in that product. And then we're getting these reactions. And then this
[00:24:24.240]hydroperoxide is actually going to start to degrade. And it breaks down into really small,
[00:24:31.820]volatile molecules, things like aldehydes and ketones. And it's these small products or these
[00:24:39.200]small breakdowns that are going to lead to really volatile off flavors or off aromas that consumers
[00:24:48.340]are going to notice. So the effect of water activity and the way that we can use water
[00:24:54.240]activity is that at lower water activity levels, less than 0.25, oxidation rates
[00:25:01.080]actually start to increase. And the reason for this is that oxygen can directly start to interact
[00:25:08.300]with those unsaturated fatty acids. So there's no protective barrier from the water and oxygen
[00:25:16.060]can get in there and start to wreak havoc. If we move at higher water activities above about 0.45
[00:25:23.820]water activity, this is where oxidation rates also increase. And this is because the oxygen
[00:25:30.940]and the water itself can start to interact with the unsaturated fatty acids. So if we were to map
[00:25:38.280]water activity versus reaction rate, you'll notice the curve here, lipid oxidation,
[00:25:43.860]it's a little hard to see, but you'll notice that we have a low point around 0.3 or 0.35
[00:25:50.420]water activity. So if you're working on a product where you're trying to reduce
[00:25:55.020]lipid oxidation, this might be the sweet spot for you to prevent that from occurring.
[00:26:00.800]And I see a lot of teams that over-dry products. They think they're okay from
[00:26:05.900]lipid oxidation because they're drying way down to 0.2 or maybe 0.1 water activity.
[00:26:12.040]But keep it in mind that this may actually be causing lipid oxidation to increase
[00:26:18.040]in that product. Next, I wanted to talk about how we can actually combine water
[00:26:25.620]activity and moisture content together. So when we do that, we have water activity
[00:26:30.660]here on our x-axis and moisture content on our y. And a lot of instruments just take
[00:26:36.800]a single water activity reading. They tell us the water activity at a specific time and
[00:26:42.360]a specific temperature. But if we were to map this entire relationship between energy
[00:26:49.020]and quantity of water, this is called a moisture sorption isotherm. And as we move along this
[00:26:55.880]curve, it can affect reaction rates. Like here's the lipid oxidation that we just
[00:27:00.520]talked about. It can affect physical changes like caking and clumping or maybe loss of
[00:27:06.400]an ideal texture. And if we go high enough on this curve, this is where mold and yeast
[00:27:11.880]and bacteria can start to grow. So we can use an isotherm as a way to balance all of
[00:27:18.860]these different safety or quality characteristics or parameters that we may be concerned with.
[00:27:25.380]Keep in mind that water activity is equal to relative humidity.
[00:27:30.380]And what I mean by that is that if you produce a product at 0.3 water activity,
[00:27:35.280]but it sits in a 60% relative humidity environment, then if you give that product
[00:27:41.460]enough time, it's going to move up this curve and equilibrate to 0.6 water activity.
[00:27:48.080]So water activity is dynamic. It's always trying to come to equilibrium with the surrounding
[00:27:54.780]environment. And that's why the packaging and monitoring your environmental conditions,
[00:28:00.240]it's so important, because water activity can change over time.
[00:28:06.180]So overall, we can use a moisture sorption isotherm to balance the safety and the quality
[00:28:12.320]of what you're working on, but also the yield and the revenue. So this gives us a way to
[00:28:17.520]talk in terms of water activity and moisture content. Right here, everything we need is
[00:28:23.180]on the same graph. I like to call isotherms a complete moisture map. They tell us everything
[00:28:30.100]that we need to know about the water in a product or an ingredient or formulation. And keep in mind
[00:28:37.100]that all of these things, ingredients, products, formulations, each of them are going to have their
[00:28:42.020]own unique moisture sorption isotherm. So it's really important that we study this for every
[00:28:48.040]individual thing that you may be working on. And we can also study these in either direction. We
[00:28:54.260]can look at them in an adsorption direction. So we can look at how water is picked up,
[00:28:59.960]and binds to a product. Or we can look at a desorption isotherm. And we can look at the way
[00:29:06.100]that water is released or removed from a product. So depending on what you're working on, and what
[00:29:11.880]the starting water activity will be, then this will kind of dictate maybe which direction we
[00:29:17.780]want to look in. When it comes to isotherms, there's basically three methods that you'll
[00:29:24.740]come across. First of all, you may be familiar with, maybe this is something that you've done
[00:29:29.820]in school or grad school, but most companies have moved beyond this, but I'm still surprised
[00:29:36.100]at a few companies that still use controlled chambers. These are basically controlled
[00:29:41.980]humidity environments where you can control the humidity inside to a certain percentage,
[00:29:48.080]and then maybe you use six to nine different chambers. It may look something like this,
[00:29:53.540]kind of an old school method, but doing this, you're just going to get a few data points,
[00:29:58.380]and then you have to try
[00:29:59.680]to model an isotherm to that data. And you see here, it does okay, but we can definitely
[00:30:05.980]do better. It requires a ton of work and a ton of time in order to make an isotherm in this way.
[00:30:13.520]The second method that came out in the 90s is called dynamic vapor sorption, or DVS. This is
[00:30:20.940]a really good method for evaluating sorption kinetics, and this is an example for spray-dried
[00:30:28.460]milk powder.
[00:30:29.540]But I just want you to bring your attention here to this red curve. So again, we might
[00:30:34.280]collect six to nine data points, but this time they all fall much better on the same
[00:30:40.200]curve.
[00:30:40.740]And then finally, the third method you may find is called a dynamic dewpoint isotherm,
[00:30:47.580]or a DDI method. This is a really high-resolution isotherm. It's really good for studying
[00:30:54.000]sorption properties in a changing environment. And for the same sample,
[00:30:59.400]I just want you to bring your attention here to the DDI curve. So this is for the same sample,
[00:31:06.100]but you'll notice that this has much more data points, usually hundreds of data points.
[00:31:11.720]And you'll see these inflection points where you get a lot of moisture uptake. And if your
[00:31:16.660]product or your sample is susceptible to physical transitions or physical changes, then this
[00:31:22.800]DDI curve can be used to pinpoint exactly what water activity ranges you need to stay
[00:31:29.260]within to avoid those physical transitions from occurring. So a DVS method would step
[00:31:35.940]right over that. You don't really see where that happens. But using a DDI is usually really
[00:31:42.400]the best starting point for most products to get an idea of the sorption properties.
[00:31:49.200]So just in summary, if we put these on the same graph, DDI maybe takes a day or two.
[00:31:54.320]It's a very high resolution where DVS is a slower
[00:31:59.120]genetic test where you're equilibrating at each step. So depending on your product
[00:32:04.580]and your research question, one of these methods may work better over the other.
[00:32:09.720]And I know I'm kind of quickly going through these today, but I just want you to know that there are different methods.
[00:32:14.620]And if you have follow up questions on these two types of methods, I'm happy to follow up with you.
[00:32:23.020]Isotherms are mainly used in research and development and product development. They're used for a very
[00:32:28.980]wide range of things to overcome different R&D challenges. Things like avoiding unwanted texture change.
[00:32:36.680]If you're trying to preserve a specific texture or flowability of a powder, then this can give you the insights you need to set the right water activity specs.
[00:32:47.180]If you're trying to evaluate a film or a coating or even an encapsulation, then isotherms can very quickly show you how well that film is keeping moisture out of something.
[00:32:58.840]Like if you're working on a seed and you want to keep water out to prevent it from germinating, or maybe you're working on something like a blueberry and you want to keep moisture inside,
[00:33:09.600]then an isotherm can help you in either of those instances to understand how well the film or the coating is working.
[00:33:17.900]Isotherms can be used to predict shelf life. So instead of waiting years for full shelf life testing or months for accelerated testing, using isotherms
[00:33:28.700]and the correct model, and using this with fixed law of diffusion, then very quickly you can predict the shelf life,
[00:33:38.260]taking into account all the storage conditions, your packaging information, and the sorption properties of the product.
[00:33:45.800]This means that we can also use this approach to optimize the packaging and make sure that you're using exactly what water vapor
[00:33:54.060]transmission rate you need in order to hit a specific shelf life.
[00:33:58.560]So this can be used to make sure that you're not over or under packaging, that you're using the right packaging for each of the formulations that you're working on.
[00:34:07.960]Isotherms can be used to assess temperature fluctuations. Temperature is always changing, especially if your product is going to go sit in a hot Amazon warehouse or something like that.
[00:34:20.300]Then using isotherms, we can predict at what temperatures will lead to different safety or quality concerns.
[00:34:28.420]Normally, isotherms are used to accelerate formulation processes, so you can use an isotherm to understand how mixing different ingredients or different final components is going to affect the overall, the equilibrium water activity.
[00:34:43.200]And you can get an idea of how moisture will migrate or move between different components or ingredients before physically having to go out and make a bunch of new things.
[00:34:54.160]So there's a lot of applications here. Again, I'm just kind of listing them out.
[00:34:58.760]But if your team struggles with anything on this list and you want to go into more details, please reach out to me and I'm happy to go through that with you.
[00:35:08.320]Okay, finally, we're going to talk about hitting moisture targets during the production process.
[00:35:15.580]So every time that I meet with a production team, these are some of the key challenges that I often hear.
[00:35:22.400]Definitely reducing variation and being more consistent.
[00:35:26.340]Maximizing the amount.
[00:35:28.380]The amount of moisture content or the amount of moisture in the product.
[00:35:32.000]Being able to avoid any rework or lost batches that may be occurring.
[00:35:38.620]It takes a lot of time and effort if you have to go back and rerun something.
[00:35:42.840]Seasonal fluctuations always tend to cause headaches.
[00:35:47.120]In hotter, more humid times of year, it's much harder to make the same product.
[00:35:53.640]And finally, training new operators is always difficult.
[00:35:56.680]There's people in our industry.
[00:35:58.240]That have been working on the same production lines for 30 plus years.
[00:36:03.540]And they're retiring.
[00:36:05.020]And we have to get somebody new in there.
[00:36:07.400]Who's able to know every detail about running the process.
[00:36:12.300]And making the product.
[00:36:13.460]And often this leads to different difficulties.
[00:36:16.360]And different wastes in the production process.
[00:36:19.240]I'm always asked about inline moisture measurements.
[00:36:23.880]Usually what some teams will try is near infrared or NIR.
[00:36:28.220]This works by taking light and reflecting it off the product that's running through.
[00:36:34.460]And then focusing that on some type of detector.
[00:36:37.960]And then you compare it to some type of internal reference.
[00:36:41.820]And this is going to be converted to a percent moisture content.
[00:36:46.160]But some of the major challenges with using NIR is that constant calibration is required.
[00:36:53.020]And if that model isn't being updated in real time.
[00:36:57.640]Then there's a lot of problems.
[00:36:58.200]And there's already an inherent bias that's occurring because of this.
[00:37:02.320]And most of these models aren't going to respond very well to variation.
[00:37:07.380]Whether it's variation in color or even distance to the product.
[00:37:11.860]And this requires that different reference values constantly be added.
[00:37:18.100]And I hardly ever see any production team really stay on top of this.
[00:37:22.680]Like we talked about earlier, this is a secondary method that requires constant calibration.
[00:37:28.180]With NIR, you're also going to see drifting that occurs.
[00:37:33.260]This happens mainly due to dirty mirrors or dirty components or even electrical drifting.
[00:37:40.480]This occurs in any type of electrical device, even devices at Aqualab.
[00:37:45.460]And this is why it's so important to constantly calibrate and verify that things are working correctly.
[00:37:51.480]The final kind of issue here is that NIR is just going to measure the percent of the
[00:37:58.160]moisture content of the top layer.
[00:38:00.660]And it's not going to take into account the average moisture content of everything going through.
[00:38:06.760]So you're just basically measuring moisture at one specific place within the samples going
[00:38:12.520]through, but you're not getting the entire picture.
[00:38:15.300]And the distance of the sensor to the product needs to stay constant.
[00:38:19.760]And this is basically impossible, especially if you're working on things like pet food or
[00:38:24.400]other types of products where things can pile up.
[00:38:27.580]And it can be very difficult to keep that distance constant.
[00:38:31.460]What we found at Aqua Lab is that instead of looking at moisture and trying to measure
[00:38:38.540]moisture in line or even trying to measure water activity in line, which is basically
[00:38:43.860]impossible because we don't have a closed chamber or a closed system, is that the key
[00:38:50.840]number to watch is actually the temperature and the temperature differential that occurs
[00:38:56.360]due to evaporative.
[00:38:57.560]Maybe this figure will help explain it a little better.
[00:39:02.100]We basically look at the temperature of the burner and then the temperature after the
[00:39:07.600]heat has gone through the wet product.
[00:39:11.040]We call this difference a delta T, a change in temperature.
[00:39:15.580]If we're monitoring this delta T at the right locations with any type of drying system,
[00:39:22.440]then we can correlate the delta T to the final moisture content.
[00:39:27.460]This allows us to go from your current control, where you may have a wider moisture content
[00:39:36.640]and more variance than you want, to improving that control and reducing the variation.
[00:39:43.340]Once we do that, then we can start to increase the average moisture content.
[00:39:49.240]When we do that, we're increasing the production.
[00:39:52.080]We're using more water instead of ingredients to make the same product, and we're also reducing
[00:39:57.360]the amount of energy that's used, maybe by 5% or sometimes around about 10%.
[00:40:04.900]This is an example of using the Delta T approach.
[00:40:08.260]This is for pet food, where the starting moisture content was 7.5%.
[00:40:14.660]You can see, even before I press play, that there's a lot of variation.
[00:40:18.740]Some of the product is under-drying, and the moisture is too high or over-drying, and we're
[00:40:24.280]going lower than this lower spec.
[00:40:27.260]Using the Delta T approach and using the information from temperature probes or sensors and turning
[00:40:33.800]on this type of solution can really help to increase the average moisture and reduce,
[00:40:42.260]make a smaller window for the upper and lower spec, and really help improve with the variation
[00:40:48.680]while increasing the average moisture content.
[00:40:52.500]So the benefits of using this Delta T approach is that it can really help to eliminate the
[00:40:57.160]over or under dried product.
[00:40:59.980]It can increase the yield and it really depends on the type of product that we're talking
[00:41:04.200]about.
[00:41:05.200]If it's a spray dried powder, then maybe we're just increasing by 0.25% and in that in itself
[00:41:11.980]may be a huge gain.
[00:41:13.580]Or if it's pet food or something else, I have seen this improve the moisture content by
[00:41:18.560]several percent.
[00:41:20.460]Using this approach is like using cruise control.
[00:41:24.020]And this means that there's less operator error.
[00:41:27.060]You just get things up and running, and then you can allow a delta T approach to take over
[00:41:31.880]and consistently hit your moisture target.
[00:41:35.860]Because we're looking at things inside the dryer and not waiting for downstream sampling,
[00:41:41.260]we have a quicker resolution of any dryer issues that may be occurring.
[00:41:46.660]It's really clear and easy to use for operators.
[00:41:50.240]And it's going to lower the overall energy consumption, maybe about 5% to 10%, depending
[00:41:56.280]on the product.
[00:41:56.960]And the dryer type.
[00:42:00.520]Dryers-- this has been used for all types of dryers.
[00:42:04.900]It looks like my camera just died.
[00:42:06.240]It overheated.
[00:42:07.400]But hopefully, you can still hear me.
[00:42:09.280]But this is going to work for all types of dryers.
[00:42:12.080]Probably the best application is spray dryers, because it's the most straightforward.
[00:42:18.080]It's really easy to find the hot and cold points.
[00:42:22.200]But this has been used on a much wider range of dryers.
[00:42:25.380]And I've just kind of listed them out
[00:42:26.860]here.
[00:42:27.860]I won't go through all of them.
[00:42:28.940]But things like belt or rotary or ring, all types of dryers.
[00:42:34.620]Basically any time that there is a longer hold time and you're running for a really
[00:42:39.520]long time, this introduces a great opportunity in order to use this approach to make these
[00:42:46.760]types of improvements.
[00:42:48.520]And then industries where this approach is already being used include the pet food industry,
[00:42:53.960]things like dried meats, nutrition bars, different
[00:42:56.760]types of baked snacks, dried ingredients, milk powders, and dried fruits and vegetables.
[00:43:03.660]And this list just continues to grow.
[00:43:05.940]This is just what I was able to kind of think of off the top of my head.
[00:43:09.460]But I know that we've worked in other industries as well, even things like pharmaceuticals
[00:43:14.120]or building materials.
[00:43:15.800]Anywhere where moisture is being removed is a great opportunity to use a Delta T approach
[00:43:22.400]instead of using NIR or waiting for downstream sampling.
[00:43:26.660]Okay.
[00:43:27.980]From here, wrapping things up.
[00:43:30.480]My camera didn't quite make it, but hopefully you're still there.
[00:43:34.160]I just wanted to wrap up by saying that overcoming moisture challenges really does require measuring,
[00:43:40.700]controlling and understanding water at every step of the production process.
[00:43:45.000]So today we talked briefly about moisture sorption isotherms and how these can be used
[00:43:50.380]for product development.
[00:43:52.200]We talked just briefly, I mentioned it earlier, but water activity can be used.
[00:43:56.560]Water can be used to really understand water's impact on different organoleptic or sensory
[00:44:01.040]qualities.
[00:44:02.980]Water activity can be used over moisture content to set specs on incoming ingredients, especially
[00:44:09.760]dry ingredients.
[00:44:11.580]Water activity and moisture can be used or they can actually be targeted and hit your
[00:44:19.760]targets using that delta T approach in production.
[00:44:23.980]We talked a little bit about different instruments.
[00:44:26.460]And primary and secondary methods, hopefully this really helps direct your quality assurance
[00:44:31.960]and quality control teams.
[00:44:34.280]And finally, packaging and shelf life.
[00:44:36.520]We didn't really get into it too much today, but the same isotherms that we used down here
[00:44:41.660]in research and development, these can be used to very quickly predict shelf life and
[00:44:47.460]optimize the packaging for the things that you're working on.
[00:44:51.540]So complete moisture control is possible, but as you see it, it requires
[00:44:56.360]understanding water activity and moisture and isotherms and the delta T approach
[00:45:01.180]and putting all of that together from start to finish.
[00:45:04.920]So I just want to finish here today by looking back at our goals and making sure that we hit on everything.
[00:45:11.600]So first, what is water activity? Water activity is a form of energy,
[00:45:17.320]and I hope you remember that next time you think about water activity or you take a water activity measurement.
[00:45:23.980]How is it different from moisture content?
[00:45:26.260]Water activity directly relates to safety and quality.
[00:45:30.900]It's a measure of energy. Moisture content is primarily used for yield and revenue, and it's expressed as a percent.
[00:45:38.400]Water activity impacts microbial growth because every microorganism has a limit.
[00:45:44.080]And if you go below a specific water activity, that microbe will no longer grow.
[00:45:49.220]So we can have something that's safe, but not necessarily sterile.
[00:45:52.960]We talked about water activity and how it impacts lipids.
[00:45:56.160]There's a sweet spot for lipid oxidation around 0.3 or 0.35 water activity where the
[00:46:02.920]reaction rate is at the lowest.
[00:46:06.140]A moisture sorption isotherm we talked about.
[00:46:08.740]This is connecting or correlating water activity to moisture content.
[00:46:13.460]There are three methods that we went over today.
[00:46:16.300]But the DDI, the dynamic dew point isotherm, is generally the best starting point.
[00:46:22.620]We talked about a whole range of different R&D challenges.
[00:46:26.060]Isotherms can solve, whether it's looking at texture change or different coatings or
[00:46:30.760]accelerating formulation processes.
[00:46:33.340]There are lots of uses for isotherms in research and development.
[00:46:38.360]And finally, variation can be reduced in production using the delta T approach.
[00:46:44.020]There is a wide range of dryers and products where this is already being applied.
[00:46:48.820]And if you're somebody that works in production or you work closely with your production teams
[00:46:53.560]and you think that this would be helpful, I'd be happy to help.
[00:46:55.960]I'd be happy to discuss that with them.
[00:46:58.780]Here's my contact information.
[00:47:01.680]If you have any questions about these slides or if you'd like a copy, please reach out
[00:47:06.160]to me, zachary.cartwright@aqualab.com.
[00:47:10.100]I also always like to promote my podcast that I work on.
[00:47:14.000]It's called The Drip.
[00:47:15.420]It uses or it discusses science, music, and mantra.
[00:47:19.500]I've interviewed lots of people within the food industry, and also we talk about different
[00:47:24.980]music.
[00:47:25.860]Different quotes or different things that bring balance to different scientists' lives.
[00:47:30.320]So if you're looking for something new to listen to, especially within the food industry,
[00:47:35.020]please check out The Drip.
[00:47:36.500]It's available on Spotify, Apple, Amazon, basically anywhere where you listen to podcasts.
[00:47:44.000]So if you have any questions, please reach out to me.
[00:47:46.940]I'll leave or finish here today with my email address on the screen.
[00:47:51.340]But thank you so much for your time, especially if you watch this.
[00:47:55.760]All the way to the end, I really appreciate that.
[00:47:58.080]So have a great one, and hopefully we'll see you in person next time at the University
[00:48:03.520]of Nebraska.
[00:48:04.520]Thank you.
[00:48:04.580]Thank you.
[00:48:04.620]Thank you.
[00:48:04.800]Thank you.

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Moisture Challenges in the Food Industry: Basics & Beyond

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