01
What is moisture?
moisture refers to the water contained within a substance. Many substances around us and in manufacturing environments, such as food, paper, wood, powders, and chemicals, contain water.
Even substances that appear dry may not be completely free of water. Furthermore, even substances of the same type can have varying moisture content depending on storage conditions, drying conditions, manufacturing conditions, and the surrounding environment.
Therefore, in manufacturing and quality control, the focus is not simply on whether or not there is water, but rather on understanding the amount of water present.
When understanding moisture, it's helpful to separate "how much water is contained in a substance" from "how that moisture is expressed numerically using a specific standard."
02
What Is Moisture Content? How to Express moisture as a Percentage
A common indicator that expresses the percentage moisture contained in a substance is "water content." However, the way the value is expressed differs depending on what mass is used as the basis.
moisture The amount and moisture content are different.
moisture Amount represents the amount of water contained in the object itself. On the other hand, moisture content represents the proportion of water contained in the object.
In the moisture-based standard, the entire moist sample is used as the standard.
In the wetness-based method, the total mass of the sample, including water, is used as the basis for expressing the proportion of water contained within it.
Moisture content based on wetness = Mass of water ÷ Total mass of sample including water × 100
The dry weight basis uses the dry state of the substance as the standard.
On a dry basis, the amount of water contained in a substance is expressed based on its dry mass.
Dry moisture content = Mass of water ÷ Mass of dry material × 100
Even with the same "moisture content of ○%", check the standards.
Because the denominators are different for wet-weight and dry-weight standards, the moisture content values will not be the same even for the same sample.
When comparing moisture values, it's important not only to look at the numbers themselves, but also to check the definitions and standards used to express those values.
03
What is the difference between moisture and humidity?
While both moisture and "humidity" are terms related to water, they primarily deal with different things.
| Item | Main target | What does it represent? |
|---|---|---|
| moisture | Food, paper, wood, powders, and other materials | The amount or percentage of water contained in a substance |
| Humidity | gases such as air | The state of water vapor present in a gas |
moisture captures the water contained in a substance.
For example, when measuring moisture of paper, the focus is on how much water is contained within the paper itself.
Humidity is the amount of water vapor in gases such as air.
On the other hand, when considering the air surrounding the paper, the state of water vapor in the air is expressed as humidity.
moisture and ambient humidity can also be factors.
While moisture and humidity are different things to measure, they are not entirely unrelated. Some substances may absorb or release moisture depending on the surrounding environment, such as temperature and humidity.
04
Why is it necessary to know about moisture?
The amount moisture contained in a substance can be related to the condition of the product or raw materials, processing, and storage.
The state of a substance changes depending on moisture
When moisture changes, the physical properties and state of the material, such as mass, hardness, viscosity, and fluidity, may change depending on the material.
Affects quality and processing condition
In the manufacturing process, differences in moisture can affect processability, finish, and product variability. Therefore, moisture content ranges are sometimes set and managed according to the specific material being worked on.
It serves as an indicator of the storage and drying conditions.
In foods, raw materials, and powders, moisture content changes due to storage and drying. Measuring moisture provides information to determine the state of the material.
Less moisture isn't always better.
When we talk about moisture management, we tend to think of "keeping things as dry as possible," but the appropriate moisture varies depending on the product and process.
Not only is insufficient drying problematic, but excessive drying can also affect quality and process. The key is to understand the appropriate moisture level for the intended purpose.
05
How do you measure moisture?
moisture measurements do not directly measure all objects using a single method. Various physical and chemical phenomena that change with moisture are used to determine moisture amount and moisture content.
What I want to know is the amount of "moisture".
The purpose of moisture measurement is to determine how much water is contained in the object being measured.
However, there isn't just one way to obtain that value. Changes in mass, chemical reactions, electrical properties, and interactions with light and electromagnetic waves that result from changes in moisture can be used for measurement.
We utilize phenomena related to moisture in our measurements.
| Phenomena and properties to be utilized | Way of thinking | Typical methods |
|---|---|---|
| Mass change | moisture can be determined from the change in mass before and after drying. | Heat drying method/drying loss method |
| Chemical reaction | This utilizes the reaction between water and reagents. | Karl Fischer method |
| Electrical properties | This utilizes the electrical properties that change with moisture. | Electrical resistance type, electrical capacitance type, etc. |
| Interaction with light and electromagnetic waves | Utilizing absorption of light and electromagnetic waves by water. | infrared absorption type etc. |
There is no single measurement method that is always the best. The most suitable method varies depending on the object being measured, moisture range, the required accuracy, the measurement time, whether or not sample collection is possible, and whether continuous measurement is necessary.
06
Typical methods for measuring moisture
There are several methods for measuring moisture. Here, we will briefly summarize what each method uses to determine moisture.
Utilizing the change in mass due to drying
One method involves drying the sample and determining moisture from the difference in mass before and after drying. Typical examples include the heat drying method and the loss on drying method.
It utilizes a chemical reaction with water.
There are methods for quantifying moisture using chemical reactions between water and reagents. The Karl Fischer method, for example, is used for measuring trace amounts of moisture.
Utilizing electrical properties
There are methods to estimate moisture by utilizing changes in electrical resistance and capacitance caused by moisture.
Utilizing the interaction with light and electromagnetic waves
Water has the property of absorption electromagnetic waves of specific wavelengths. There are methods that capture such optical changes and determine measurements in relation to moisture.
Infrared-based methods can measure moisture without contact with the object, and are sometimes used for continuous measurements on manufacturing lines.
07
When and where you measure moisture is also important.
Even though both involve moisture measurement, the purpose differs depending on whether you're taking a sample and examining it in detail, or continuously monitoring its state during the manufacturing process.
Take a sample and measure it.
One method involves taking samples from raw materials, process products, and finished products, and measuring their moisture. This can be used to determine the state of a sample at a specific point in time.
Measured during the manufacturing process
Measuring moisture on the manufacturing line can sometimes provide a continuous view of how moisture changes during process.
The information obtained from point measurements and continuous measurements differs.
Measuring samples at regular intervals allows you to check moisture at each point in time. On the other hand, continuous measurement allows you to understand the changes in moisture content over time, including the changes that occur between samples.
Neither method is always superior to the other; they are used interchangeably or in combination depending on the measurement purpose.
FAQ
Frequently Asked Questions about moisture
Are moisture and humidity the same thing?
They are not the same. moisture primarily refers to the water contained in a substance, while humidity primarily refers to the state of water vapor present in gases such as air.
What is moisture content?
Moisture content is expressed as the percentage of water (moisture) contained in a substance. There are two main methods: the wet-basis method, which uses the total weight of the wet sample as the reference, and the dry-basis method, which uses the weight of the dry substance as the reference. When comparing values, it is necessary to confirm which method was used to express them.
Is it possible for the moisture content to exceed 100%?
In the dry weight basis, the mass of water is expressed as the ratio of the mass of the dry substance, so if the mass of water exceeds the mass of the dry substance, the percentage can exceed 100%. On the other hand, in the wet weight basis, where the entire wet sample is used as the denominator, the percentage will not exceed 100%.
How do you measure moisture?
Methods include utilizing mass changes due to drying, chemical reactions with water, changes in electrical properties due to moisture, and interactions with light and electromagnetic waves. The most suitable method varies depending on the object being measured and the purpose.
Is it better to have less moisture?
Not necessarily. The appropriate moisture range varies depending on the product, raw materials, and manufacturing process. Not only insufficient drying, but also excessive drying can affect quality and process.
Next
What I want to know next about moisture
Once you understand the basics of moisture, moving on to "how to measure it" and "how to measure it in the manufacturing process" will make it easier to understand the overall picture of moisture management.
Learn how to measure moisture.
This document outlines representative methods and selection criteria for moisture measurement, including drying, chemical reactions, electrical properties, and infrared radiation.
Learn more about the difference between moisture and humidity
You can review the basics of how to represent water vapor in the air, including relative humidity, absolute humidity, and dew point.
Measuring moisture during the manufacturing process.
This article explains in detail the differences between sampling and online/continuous measurement, and where in process moisture should be measured.
Learn about measurement using infrared rays
By utilizing the interaction between infrared radiation and matter, it is possible to measure not only temperature but also moisture, constituent, thickness, and coating amount.
