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Head officeF2-2-15 Houshin,Higashiyodogawa,Osaka,Japan
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Questions and Answers


Q.1 How should we re-use desiccants in food packages?

If the effect remains, desiccants can be re-used for storing foods and drying shoes at home.

In lime desiccants (RAYM®), granular calcium oxide turns into powdery calcium hydroxide as it absorbs moisture. If a packet's contents sound granular when shaken, it is still effective.

Blue SILICA GEL gradually turns pink as it absorbs moisture. Pink SILICA GEL is no longer effective.

DESI PAK shows no changes in shape or color. The residual effect cannot be judged by appearance.

Q.2 How should we dispose of desiccants?

Dispose of desiccants as non-combustible waste.

When a large amount of desiccants are to be disposed of industrially, they should be treated as industrial waste.

Lime desiccants (RAYM®) should be disposed of where no water is present, as the material calcium oxide generates heat when it comes into contact with water.

Q.3 What should we do when a lime desiccant is ingested by mistake?

Desiccant composed of calcium oxide reacts with water and generates hydration heat. In case burns are suspected, seek medical advice.

If the contents have already adsorbed moisture and turned into powder (calcium hydroxide), gargling is normally sufficient. Calcium hydroxide is non-toxic and approved as a food additive. However, its aqueous solution is strongly alkaline and irritates mucous membranes. If swallowed, drink milk or water with egg-white (one egg-white mixed in a glass of water) and seek medical advice.

Q.4 What should we do when SILICA GEL or DESI PAK is ingested by mistake?

SILICA GEL and DESI PAK are inactive and chemically stable. They are not digested or absorbed in the body.

If ingested by mistake, gargle with water and drink water, milk, or tea. In case of contact with the eyes, wash with plenty of tap water without rubbing with hands.

Q.5 What should we do when a desiccant is cooked with food and ingested?

Desiccants contain no toxic substance. Cooking can cause the contents to seep out from the packet, but they have no adverse effects on the human body.

No special treatment is necessary. If you are worried, seek medical advice and show the packet to the doctor.

Q.6 A desiccant packet swelled in a food package. Why?

The swelled packet is a lime desiccant.

The main component in lime desiccant is calcium oxide. It chemically turns into calcium hydroxide by absorbing moisture. During the process, granules turn into powder, increasing 2 to 2.5 times in volume.

Therefore the packets are made large enough to accommodate the fully swollen contents without puncture following moisture absorption.

Reaction formula: CaO + H2O = Ca (OH)2

Q.7 How should we discriminate between desiccants and oxygen absorbents?

Desiccants keep the humidity in the package low by adsorbing water vapor to prevent moistening of the food.

Oxygen absorbents prevent oxidation, discoloration and molding of foods by absorbing oxygen.

These should be used according to the properties of the food and purpose of storage. Typical applications are given below:

Application to foods



Typical applications

Moisture prevention



Dried laver, rice crackers, cookies, dried mushrooms, freeze-dried foods, health foods.

Mold prevention


Oxygen absorbent

Savory delicacies, dried small sardines, dried mushrooms, dried noodles.

Steamed buns stuffed with bean jam, Western-style confectionery, dried small sardines, uncooked noodles, soybean paste, savory delicacies.

Discoloration/deterioration prevention


Oxygen absorbent

Candies, savory delicacies, dried mushrooms, sesame seeds.

Dried laver, nuts, savory delicacies, processed meat, sesame seeds.

Insect damage prevention

Oxygen absorbent

Cereals, nuts, sesame seeds, dried mushrooms, fodder.

Non-food application



Typical applications

Moisture prevention


Plastic films, resin materials, pharmaceuticals.

Mold prevention


Oxygen absorbent

Artifacts, woodwork, bamboo ware, leather goods.

Textiles, leather goods, pet food.

Corrosion/fogging prevention


Metal parts, electronic appliances, precious metals, glass ware.

Condensation prevention


Air cargo, container transportation, glass ware.


/deterioration prevention

Oxygen absorbent

Pharmaceuticals, herbal medicines, cosmetics, dyestuffs.

Q.8 What are the types and characteristics of desiccants?

Desiccants are classified into chemical desiccants and physical desiccants. Chemical desiccants, such as RAYM®, adsorb moisture by being combined with water through a chemical reaction.

Physical desiccants, such as DESI PAK and SILICA GEL, adsorb water vapors in capillary pores without changes to the substances.

Product name

Main component

Absorption capacity



Appearance of material


Calcium oxide



+ +

Changes from granules (CaO) to powder (Ca(OH)2)




+ + +

+ +


Silica Gel

Silicon dioxide


+ +



Q.9 Can desiccants be reactivated?

Lime desiccants (RAYM®) cannot be reactivated, as moisture absorption changes the substance from calcium oxide to calcium hydroxide.

Physical desiccants (DESI PAK® and SILICA GEL) can be reactivated by heating, as moisture adsorption does not change the substances. However, it is necessary to heat desiccants for packaging for a long time at a relatively low heat (below 100șC), as the packets are made of plastic film or unwoven fabric.

Q.10 Lime desiccants are made of calcium oxide, which rapidly generates heat when it comes into contact with water. What are the safety measures taken by the manufacturers?

NSKK, the council organized by lime desiccant manufacturers, provides the following standard for packet materials to ensure safety.

NSKK strength standard

Test item


Tensile strength




4.0 kg




3.0 kg


Burst strength


2.5 kg. cm2

Bonding strength/15 mm

0.6 kg

Q.11 What is the difference between Type A and Type B SILICA GEL?

SILICA GEL is classified into two types: one having a high moisture-absorbing capacity at low humidity and the other having a high capacity at high humidity. The former is referred to as Type A SILICA GEL and is used as a desiccant for storage of food and metal parts.

The latter is referred to as Type B SILICA GEL and is used for moisture control.

Type A simply adsorbs water vapor in the atmosphere in a normal humidity range. Type B adsorbs water vapor at high humidity and releases it at low humidity.

The name "SILICA GEL" for desiccants generally refers to Type A.

The capacity of SILICA GEL is standardized by the JIS as follows:

Test item



Moisture absorption at 20% RH (%)

8 min.

3 min.

Moisture absorption at 50% RH (%)

20 min.

10 min.

Moisture absorption at 90% RH (%)

30 min.

50 min.

Water content (%)

2.5 max.

2.5 max.

pH value

4 to 8

4 to 8

Specific resistance (

3000 min.

3000 min.

Q.12 What is the difference between the two physical desiccants, SILICA GEL and DESI PAK®?

Both SILICA GEL and DESI PAK® are referred to as physical desiccants, as they physically adsorb water vapor in the air into their capillary pores.

SILICA GEL is made of quartz sand, a soil component, chemically treated into silicon dioxide with a high purity. It is formed into beads having capillary pores.

DESI PAK® is an activated special soil component having capillary pores. It is referred to as a clay-type physical desiccant.

Q.13 How should we store desiccant packets remaining in opened packages?

If desiccants are left in the atmosphere, they absorb water vapor in the air and lose their drying capacity. Close the plastic bag containing the remaining packets tightly, e.g., with a rubber band, and store in a dry, cool place.

Q.14 Which are more suitable for corrosion prevention of metals, desiccants or oxygen absorbents?

The major cause of rust (oxides) is the presence of oxygen and water (water vapor). Corrosion can be prevented by removing either of the two.

When oxygen absorbents are used, the packaging material is required to be of a high oxygen barrier property. Care should be exercised in handling the packages, as defective sealing or a pinhole jeopardizes the oxygen barrier effect. Also, components of oxygen absorbents can cause discoloration of certain metals. This should be avoided by actual packaging tests before the application.

Though desiccants require a packaging material with a high moisture resistance, they are more economical than oxygen absorbents. Defective sealing and pinholes are of course undesirable, but not so jeopardizing as in the case of oxygen absorbents. Safety can be ensured by using a slightly larger amount of desiccant than required where moisture penetration is of concern.

Q.15 What desiccants are suitable for preventing metal corrosion?

MIL (Military specifications) of the United States requires desiccants to be nondeliquescent. Desiccants made of deliquescent salts, such as the calcium chloride type, are not suitable for storage of metal products, as the resultant liquid can accelerate corrosion if it comes into contact with metal.

SILICA GEL is made of an acid material. It is therefore undesirable that SILICA GEL should be in contact with metal products for a long time, even if it is enclosed in packets.

Clay type desiccants, such as DESI PAK®, can be used safely with metal products, as they are nondeliquescent and nearly neutral. They scarcely cause corrosion, even if the contents come into contact with metal.


Q.1 Can oxygen absorbents in food packages be re-used?

Oxygen absorbents cannot be re-used, as their effect is lost during the initial use.

Q.2 How should oxygen absorbents be disposed of?

Oxygen absorbents should be disposed of at home as non-combustible waste. (Though organic oxygen absorbents can be incinerated, they are normally indistinguishable from ferrous oxygen absorbents.)

When a large amount of oxygen absorbents are to be disposed of after industrial use, they should be treated as industrial waste.

Q.3 What should we do when an oxygen absorbent is ingested by mistake?

Both ferrous and organic types are not digestible in the body. They are naturally excreted.

If swallowed by mistake, gargle with water and drink water, milk, or tea. Consult your doctor, if you are worried.

Q.4 Why did an oxygen absorbent generate heat when it was taken out of a food package?

Oxygen absorbents absorb oxygen within the package by the reaction of organic substances or iron with oxygen. This reaction is associated with heat generation. If an oxygen absorbent packet has a residual capacity of oxygen absorption, it can start the reaction when the package is opened. However, this heat generation is not so rapid as to ignite the packet or cause burns to your skin.

Q.5 Why are packages of dried small sardines and mushrooms often found vacuumized?

Vacuumized packages can contain oxygen absorbents to retain the quality of the contents. Let us explain this taking dried small sardines (niboshi) as an example.

Deterioration of niboshi comprises mold growth, oxidation of fat, and discoloration. These can be prevented by removing oxygen within the package.

Methods of retaining the quality of niboshi include (1) enclosing a desiccant, (2) replacing the air with inert gas, and (3) enclosing an oxygen absorbent, and combinations of these.

(1) Enclosure of a desiccant prevents mold growth by keeping niboshi in a dry condition. However, care should be exercised, as excessive drying can cause detaching of sardine heads and weight loss.

(2) Replacement of air with inert gas is a method in which air in the package is replaced with gas having no reactivity, such as nitrogen, to reduce the oxygen concentration in the package, thereby preventing oxidation of niboshi. However, complete removal of oxygen from the package is difficult, and oxygen penetrating through the packaging material during storage cannot be removed. This method is therefore not suitable for long-term storage.

(3) Enclosure of an oxygen absorbent not only removes all oxygen initially present in the package but also continues to remove oxygen penetrating through the packaging material by its residual capacity. For this reason, this method is considered optimum for long-term storage.

Q.6 Can oxygen absorbents be heated in a microwave together with food?

Oxygen absorbents should be removed from the food before heating in a microwave, as the packets can burst or ignite.

Certain types of oxygen absorbents can be heated in a microwave. Follow the instructions on the package.

Q.7 What are the types and characteristics of oxygen absorbents?

1) Oxygen absorbents are classified into ferrous and organic types.

The former utilizes the reaction of iron absorbing oxygen when it is oxidized.

The latter utilizes the reaction of organic matter absorbing oxygen when it decomposes.

The ferrous type generally absorbs oxygen more quickly and is more economical. However, the involvement of iron powder inhibits the use of metal detectors for final checking of products. On the other hand, organic oxygen absorbents are compatible with metal detectors.

2) Oxygen absorbents are also classified into self-reacting and water-dependent types.

The ferrous type requires water for its deoxidizing reaction. The self-reaction type contains water added to the oxygen absorbent, whereas the water-dependent type uses water contained in the food in the package.

The organic type is included in the self-reaction type. Some require water for a deoxidizing reaction, but others do not. The type that does not require water is suitable for dried food.

3) Organic oxygen absorbents include a type that generates carbon dioxide.

This is referred to as the hybrid function type, which generates the same amount of carbon dioxide as the absorbed oxygen. This maintains the gas volume at a constant level in the package and prevents the gas loss phenomenon. *See Q5 and Q11.

Various types are available for products having various water activity and oil content. We recommend that the performance of the oxygen absorbent be always confirmed by preliminary packaging tests.

Q.8 We use a ferrous oxygen absorbent for our food products. What should we do if we introduce a metal detector to the production line to check metal pieces mistakenly mixed in the products?

Ferrous oxygen absorbents are incompatible with metal detectors, as they respond to it. You should use organic oxygen absorbents, such as TAMOTSU®.

Q.9 Can oxygen absorbents and desiccants be used together in the same packages of dried foods?

When desiccants are used with general oxygen absorbents, they adsorb the water that is necessary for the oxygen absorbents, lowering the capacities of both. It is therefore not desirable to use them together for long-term storage of foods.

Since TAMOTSU® D Type does not require water for its oxygen-absorbing reaction, it is compatible with desiccants and causes no capacity loss. The use of TAMOTSU® D Type in combination with a desiccant is effective for quality retention of low moisture foods, such as dried laver, rice crackers and tea, as well as pharmaceuticals and herb medicines.

Q.10 We want to use an oxygen absorbent for our new product. How should we select the type and size?

A suitable type should be selected according to the water activity of the food and insertion time. Individual conditions may affect the selection.

Select a size (air capacity or oxygen capacity) larger than the volume of air (oxygen) enclosed with the food. Care should be exercised, as manufacturers use either air capacity or oxygen capacity to indicate the size of oxygen absorbents. Their relationship is as follows:

Air capacity / 5 = Oxygen capacity

Oxygen capacity x 5 = Air capacity

Q.11 How should the air loss phenomenon be avoided?

Oxygen absorbents enclosed in a package absorb oxygen, which occupies 1/5 of the air, reducing the air volume by 1/5 (air loss phenomenon). The following methods are available to avoid this:

1) Use of the type generating carbon dioxide gas

There is a type of organic oxygen absorbent that generates the same amount of carbon dioxide gas as the absorbed oxygen.

2) Combination with inert gas replacement

Replacement of air in the package with inert gas, such as nitrogen, is available as a method for preventing oxidation of the food in the package. However, it is difficult to remove all oxygen from the package, and oxygen gradually penetrates through the packaging material. It is therefore necessary to use oxygen absorbents as well for long-term storage of the food.

* Do not use under-capacity packets of oxygen absorbents to avoid the air loss phenomenon. Residual oxygen in the packages and oxygen penetrating through the packaging material cause deterioration of the product.

Q.12 Do oxygen absorbents prevent fermentation?

It is difficult to inhibit the propagation of facultative anaerobic bacteria, such as yeast that entails fermentation.

Take measures to prevent the propagation of such bacteria, such as reduction in the initial number of bacteria on the food, review of the ingredients of the food and low-temperature distribution.

Methods of inhibiting fermentation by the use of food additives are also available. Contact us for details.

Packaging Materials

Q.1 We want to use an oxygen absorbent for our product. What packaging material is required?

Select a packaging material with low oxygen permeability given below:

(1) Packaging material laminated on polyvinylidene chloride-coated (K-coat) film

(2) Packaging material laminated on aluminized film

(3) Packaging material laminated on aluminum foil

(4) Packaging material laminated on special film with low oxygen permeability, such as EVOH

Typical combinations of packaging materials suitable for oxygen absorbents:

<KON/PE>, <KOP/CP>, <KPET/PE>, <PET/aluminized film/PE>

Typical packaging materials not suitable for oxygen absorbents:

<OP/CP>, <OP/PE>, <ON/PE>, <cellophane/PE>, <PET/PE>, partly coated bags, PE bags, packages not heat-sealed.

Airtightness should be ensured for metal cans and molded plastic containers as well.

Care should be exercised regarding the packaging forms and distribution methods, as pinholes and defective sealing of packaging materials jeopardize the effects of oxygen absorbents.

Q.2 How should we prevent condensation on packaged vegetables and fruits?

When food with a high water content is enclosed, water vapor from the food can increase the relative humidity in the packages to above 100%. This causes condensation on the inner surfaces of the packages. Such condensation water coming into contact with the food or being collected at the bottom can deteriorate the food. The use of a desiccant or water-absorbing sheets may reduce such condensation, though this is dependent on the type of food.

Another solution is the use of a gas-permeable material, such as perforated film, instead of airtight packaging. This allows water vapor to leave the packages, inhibiting condensation.

Compiled November 1, 2011

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