10-POINT GUIDE TO IMPROVING PRODUCTIVITY WITH HUMIDITY IN FOOD MANUFACTURING

MANAGE HUMIDITY, INCREASE PROFITABILITY

The water content of food is a deciding factor in its appearance, taste, shelf-life and ultimately its weight. Fruits and vegetables can be as much as 80-99% water, while foods such as meat, fish and pasta can be between 50-79% water.

For food manufacturers, managing the water content of their product is a vital strategy in maximising yield and maintaining quality. Evaporative losses and moisture gain can occur whenever the surface of the produce is exposed to the atmosphere.

The two main factors that influence the volume and speed of water movement from and into food produce are the relative humidity of the surrounding atmosphere and the duration of exposure.

This document presents an introductory 10-point guide for food manufacturers on understanding humidity and proactively managing it to enhance productivity, reduce waste and maintain product quality.

Source: The USDA National Nutrient Database for Standard Reference

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1. What is Relative Humidity?

Absolute humidity: The amount of water air contains, e.g. 5g.

Relative humidity: The amount of water air contains, expressed as a percentage of the maximum amount it could contain at the same temperature, e.g. 50%RH.

The amount of water air can hold depends on its temperature. A volume of cold air can physically hold less water than the same volume of hot air. So heating air increases the amount of water it can hold and, vice versa, cooling air reduces its ability to hold water.

Heating air does not remove water from it. As the air temperature rises, its capacity for absorbing water increases and, unless more moisture is added, its relative humidity drops.

However, as this process happens, if the air comes into contact with anything that has a greater moisture content than itself, the air will absorb moisture from the product in question until an equilibrium is reached.

Understanding temperature's impact on air humidity and this movement of moisture is very important when considering the effects of humidity on a food production area. It also highlights the need to investigate and understand the temperature and humidity profile across the area.

Textual description of diagram: Air at 2°C showing 100% relative humidity with 5g water vapor, indicating it can hold 0% more water. Air at 10°C showing 50% relative humidity with 5g water vapor, indicating it can hold 50% more water. Air at 20°C showing 25% relative humidity with 5g water vapor, indicating it can hold 75% more water. This illustrates that cold air can physically hold less water.

2. Why is Indoor Air Drier in the Winter?

As the outside air is cold in the winter, the amount of moisture it can physically hold is low. Even though the amount of water vapour in the air is low, its cold temperature means the outdoor air will be at near saturation point with a high relative humidity.

Cold winter outdoor air has very little capacity to absorb any further moisture. This is evident when you hang wet washing outside on a cold day and it takes a very long time to dry.

However, when cold winter air enters a building and is heated, its relative humidity drops because its capacity to hold moisture increases.

For instance, when a metre cube of cold outside air at 0°C and 80%RH enters a building and is heated to 20°C, its relative humidity could drop to around 20%RH. It could potentially hold 80% more moisture.

At this dry condition, the air will draw moisture from any available source it comes into contact with. In a food production environment, this includes any moist food product being processed that is exposed to the atmosphere.

Ventilating a heated production area during the winter, by leaving doors and windows open, will not raise the indoor relative humidity and solve this dry air problem. The more cold outdoor air that enters and is heated, the more moisture will be absorbed by the airflow and drawn from the food produce.

Textual description of diagram: Illustration showing a window with cold, humid air (0°C, 80%RH, 3g water) outside and warm, dry air (20°C, 20%RH, 3g water) inside, with text indicating relative humidity drops as capacity increases.

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3. What are the Benefits of Managing Humidity?

Humidity control has many benefits in food production but ultimately the objective is to improve productivity and maintain optimum product quality. Some benefits are quite specific to a production process, like using steam to stop produce sticking to its conveyor, but others are more widely employed.

Here is a selection of the most common reasons for humidity control in food production facilities, across both humidification and dehumidification.

“improve productivity and maintain optimum product quality”

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4. What is the Ideal Humidity Level?

The ideal air humidity for any food production area will depend on the objectives of the manufacturing application and the moisture content of the product.

For instance, if the objective is to prevent evaporative losses from a product and maintain its weight, the air's humidity level is determined based upon the product's ideal internal moisture content.

An equilibrium needs to be maintained between the product and the atmosphere, at a level that prevents moisture being transferred from product to air or vice versa. A graph called a sorption isotherm shows for any product, what the air humidity should be to maintain a specific internal moisture content (see fig 1).

This internal moisture content is often referred to as the equilibrium moisture content (EMC).

Besides from preventing evaporative losses, many food production processing require a specific humidity level to facilitate a reaction or effect in the produce. For instance in bread production, humidity control during dough proofing will prevent a skin from forming on the dough. While at a later stage in the production, humidity control during oven baking slows moisture evaporation to maintain an optimum baking time, as well as determining the properties of the crust.

Table 1 gives some examples of typical humidity levels in a variety of food production applications.

Textual description of diagram: Fig. 1 - Moisture sorption data (median values between wetting and drying) in atmospheres of various relative humidities, showing curves for different fruits and products against relative humidity.

“equilibrium needs to be maintained”

5. Do I Need to Humidify or Dehumidify and by How Much?

Once an ideal air humidity level has been determined for a specific process or area, it is necessary to calculate whether you need to add moisture (humidify) or remove moisture (dehumidify) to maintain this level.

This may seem obvious for an open area like a warehouse, but for more enclosed or extreme conditions, it may not be so clear. For instance, 15%RH may seem like a low humidity but to maintain this level inside an oven would normally require the addition of moisture due to the high temperature.

A psychrometric calculation must be performed that determines the difference in air moisture content from a starting temperature and relative humidity condition to the desired condition.

This calculation will take into account the volume of air involved, the start and end air conditions and all external factors that influence the air. These external factors could include the number of air exchanges an area experiences, the outside air's temperature and humidity, and any existing available sources of moisture in the area.

This calculation should be carried out by a humidity control professional. It will result in a volume of moisture per hour that needs to be added or removed from the atmosphere. This then determines the size of the humidifier or dehumidifier that must be employed to achieve the perfect environment.

Textual description of diagram: Example psychrometric calculation chart showing dry bulb temperature on the x-axis and moisture content on the y-axis, with lines indicating desired room condition (80%RH, 30°C) and outside air condition (40%RH, 38°C).

“a psychrometric calculation must be performed”

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6. Does Product Temperature Affect Air Humidity?

If an object's temperature is different from the ambient room temperature, then the air coming into contact with the object will be affected. It will either be warmed or cooled, with subsequent effects on the air's relative humidity and potentially the object.

For instance, a cold item will lower the temperature of the air that comes into direct contact with it. As cool thermal energy passes from the object to the air, a cold micro-climate results. The conditions in this micro-climate will be different from the ambient conditions of the room. Along with a lower temperature, a higher relative humidity will occur.

We see this effect on a cold glass on a summer's day. As the air next to the glass cools, its relative humidity rises to saturation point. The water the air contains can no longer be accommodated by the cold air. As the relative humidity rises to dew point, the air's moisture condenses on to the glass' surface, making the glass wet.

Likewise an item that is warmer than its environment will create a warm micro-climate with a lower relative humidity than the ambient atmosphere. This can cause a product to dry, as moisture is drawn from its surface.

So even when a production area's humidity level is at a supposedly optimum condition, a temperature difference between produce and air can cause production issues with either evaporative losses or moisture gain. The greater any temperature difference is, the greater this negative effect.

Textual description of diagram: Two circular diagrams illustrating micro-climates. The left shows a product at 38°C in an ambient room at 4°C, 80%RH, leading to EVAPORATION from the product. The right shows a product at 4°C in an ambient room at 24°C, 45%RH, leading to CONDENSATION on the product. These illustrate evaporative loss and condensation issues due to temperature difference.

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7. What Humidifier Options Are There?

Humidification systems can introduce moisture directly to a room or into a central air handling unit (AHU). To introduce water to the air it can be boiled and released as steam, evaporated from a wet surface, or turned into an aerosol.

Steam humidifiers generate their own steam by using electricity or gas to boil water. Alternatively, they can use a building's existing supply of steam to provide sterile humidification. Steam can be supplied directly from the humidifier to the room via a fan unit, or into a central AHU with steam pipes.

Steam humidifiers are frequently used for small or medium sized facilities, if particularly close humidity control is required or for specific applications, such as ovens, where a steam pipe provides a more practical solution.

Textual description of image: Industrial steam humidifier pipes installed in a food production facility.

Evaporative humidifiers are typically used in AHUs and offer high output and low energy operation. Air passing through the AHU travels through a moist evaporative cassette, absorbing water as it does so.

Textual description of image: A portable evaporative humidifier unit with a water tank.

Spray humidifiers are often used in larger commercial or refrigerated areas. Spray systems can either pressurise the water with a pump to create an aerosol, which is released from a series of nozzles, or combine it with a compressed air supply to atomise the water.

Ultrasonic humidifiers use a rapidly oscillating diaphragm submerged in water to create a mist. This is dispersed into the air with a fan. These types of humidifiers are frequently used in refrigerated displays or cold areas, as the mist has a very small droplet size that is readily absorbed by the cold air.

Textual description of image: Close-up view of an ultrasonic humidifier's internal components, showing a diaphragm and water.

“introduce moisture directly to a room or into a central air handling unit”

8. What Dehumidifier Options Are There?

To remove moisture from an atmosphere it can either be condensed out on a cold surface or absorbed by a desiccating substance. Commercial dehumidifiers use one of these two strategies to lower an atmosphere's humidity level.

In deciding which technology is most appropriate for a food manufacturing application, it is important to consider the required humidity level and the room temperature. Condensing dehumidifiers are ideal for areas that require a humidity of 50%RH or more and ambient temperatures of above 15°C. Below these levels desiccant systems are often more effective.

Both systems can be employed as direct room dryers or connected to a building's central air handling system.

“commercial dehumidifiers use one of these two strategies”

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9. What Hygiene Measures Are Required?

The hygienic operation of any food production environment is paramount. Any humidity control system employed must be capable of maintaining exceptionally high hygiene standards.

Besides concerns around the physical construction of the unit, and ensuring the materials are food grade, the main hygiene consideration is associated with the potential for bacterial build-up in any water system.

As most commercial dehumidifiers send their waste water directly to drain or vent it outside, the potential for microbial growth, and subsequent release into the atmosphere, is minimal. As humidifiers are introducing potentially inhalable droplets into an atmosphere, the risk associated with these systems should be considered.

Steam humidifiers boil water and produce sterile steam for humidification, so they present minimal hygiene risk. Evaporative humidifiers are typically located in an air handling unit (AHU) and do not produce respirable aerosols, so also present little risk to health. Although, it is worthwhile considering whether airborne pollutants, returning from the manufacturing area to the AHU, could be a potential source of nutrients on the surface of the evaporative media and cause unhygienic operation.

Spray and ultrasonic humidifiers should always be run on a potable water supply and include water filters to prevent contaminants from entering the system. Alongside a fresh filtered water supply, the humidifier must incorporate automated flush and drain cycles to ensure water entering the humidifier cannot remain static in pipework during periods of non-operation.

Additionally water treatment systems can be employed to treat the water, either with silver ion or ultraviolet sterilisation. This kills or inactivates any remaining microorganisms.

Any humidification or dehumidification system operated in a commercial premises must be regularly serviced in line with the manufacturer's recommendations. This should include disinfection of any wetted surface.

When installed, operated and maintained correctly, humidity control systems create a healthier environment for staff.

Textual description of image: Circular graphic with 'QUALITY H2O APPROVED' text and a water droplet symbol, representing hygiene standards.

“exceptionally high hygiene standards”

10. What's the Payback of a Humidity Control System?

Many food manufacturers experience financial losses by not understanding and proactively managing their factory's humidity levels. Losses from production issues are simply accepted as an unavoidable part of the manufacturing process. Investing in humidity control systems can provide rapid return on investment but before setting out on a project, it's helpful to fully explore the benefits and costs.

Financial benefit will obviously come from the primary objective for the humidity control system. If this is to prevent evaporative losses the calculation can be relatively simple, based upon the expected improvement in yield.

It is important to consider whether the improvement in yield is based upon the sales value of the final product or the value of the primary ingredient/s needed to make up the loss.

Alongside, the enhanced yield, is there any improvement in the energy or labour costs required as a result of this improved productivity? For instance, machine downtime to correct a problem or having to waste a percentage of a production run, can all take its toll on the overall efficiency of a manufacturing operation.

When reviewing the cost of a humidity control system, it is important to consider not just the initial purchase price but also the energy consumption, installation cost, commissioning (if required), routine servicing and whether any consumable components are regularly needed.

Textual description of image: Close-up of raw meat cuts, representing potential yield loss due to improper humidity.

Textual description of image: A smiling baker holding fresh bread, symbolizing improved product quality and productivity.

Textual description of image: A close-up of artisanal cheese, representing products where precise humidity control is crucial for quality.

“rapid return on investment”

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