Moisture Measurement

What is Moisture?

Moisture is defined as amount of water that can be removed from air, solid or liquid(non water) without alternation of chemical structure of air solid or liquid (non water). 

Moisture Content Representation:

  1. Moisture Content (wet basis, %)
  2. Moisture Content (dry basis, %)

1. Moisture Content (wet basis, %):

The moisture content on the wet basis is obtained by dividing the weight of water present in the material by the total weight of material.

Moisture Content (wet basis)% =(Ww/Ww+Wd)x100

Where,      Ww is weight of water in material.

                   Wd is weight of dry matter in material.

2. Moisture Content (dry basis, %):

The moisture content on the dry basis is obtained by dividing the weight of water present in the in the material by the weight of  dry matter of material. moisture measurement

                                              Moisture Content (dry basis, %)=( Ww/Wd)x100

Where,      Ww is weight of water in material.

                   Wd is weight of dry matter in material.

Moisture Measurement Method

There are two methods of moisture measurement

1.Direct methods:-Direct Method can be classified into 3 method of moisture measurement.

(I) Oven Method

(II) Brown duvel Fractional disttilation method

(III) Infra red method

2.Indirect Methods:-There are 3 types of indirect method

(I) Electrical Resistance method

(II) Dielectric Method

(III) Chemical method

1.Direct methods

(I)Oven Method :

Oven method is also have 3 Types

(A) Air oven method

(B) Vacuum oven method

(C) Water oven method

(A) Air oven method:

(a) One stage method: It is used for grains under 13% moisture content.

Procedure-

  • Take 2-3 grams of represntative ground sample of grain.
  • Place this sample in a air oven at 130°C for about 1-2 hours.
  • Afterwards the sample are taken out placed in desiccators to cool down.
  • The drop in weight of grain is measured.
  • Moisture content of material is based in the difference between the initial weight and final weight of grains.
air oven method

(b) Two stage method: it is used for grains abobe 13% moisture content.

Procedure-

  • Take 25-30 grams of whole grains sample.
  • Place this sample in an oven at 100°C for 72-96 hiurs.
  • Take out the sample from oven and placed in desiccators to cool down.
  • The drop in weight of grain is measured.
  • Moisture content of material is based in the difference between the initial weight and final weight of grains.
(B)Vacuum oven method:

It is used for fruits and vegetables

Procedure-

  • In this method, 2-3 grams of representative sample of ground material is placed in vacuum oven(25mm vacumm) at 100°C for 72-96 hours
  • The drop in weight of grain is measured based on its initial weights
(C)Water oven method:

When warm or hot water( about 100°C) is circulated around the walls to heat the oven. This method maintains more unifrom temperature than air oevn method.

Procedure-

  • Place 25-30 grams sample in an oven at 100°C for 72-96 hours.
  • Measure the drop in weight.
(II) Brown duvel Fractional disttilation method:

In this method moisture is removed by heating the grains in oil and determining the volume or weight of water removed from the grain in condensed vapour or from the loss fo weight of the sample.

Brown duvel Fractional disttilation method

Procedure-

  • Take 100 grams of whole grains sample along with 150ml of mineral oil in a flask.
  • Boil the sample, so that moisture from the sample is evaporated, collected and condensed in graduated cylinder.
  • The milimetre of moisture collected shows the percentage of moisture content
  • The determined moisture content is on wet basis.
  • In this method the temperature of mineral oil in flask should reach to 200°C within 26 minutes.
  • The time required for moisture determination is about 30 minutes.
  • If the temperature of mineral oil reaches to desired temperature within time, the moisture contenent determination is found to be fairly accurate.
(III) Infra red method:

In this method, grain moisture content is directly measured by evaporation of water from a sample of grain with an infra red heating lamp. A commercial infra red moisture meter is also available in market.

Infra red method

Procedure-

  • The instrument consists of a balance, a pan counter balanced by a fixed weight and a variable length of weighing chain.
  • An infra red lamp is mounted on an arm above the pan with provision to change its heights.
  • A scale corporate in percentage moisture content is incarnated in the stem of the instrument.
  • At the end of the test when the balance is zeroed, a direct reading of moisture content is obtained.
  • The sample of grains may be ungrounded, but when ground sample is used, the time needed to evaporate the water is reduced.

2.Indirect Methods:

There are 3 types of indirect method

     (I) Electrical Resistance method

    (II) Dielectric Method

   (III) Chemical method

(I)Electrical Resistance method:-

The electrical resistance or conductivity of a product depends upon its moisture contents. Resistance is an electrical quantity that measures how the material reduces electric current flow through it. This principle is used in resistance measuring devices. The moisture meter measure the electrical resistance of the material and is calibrated against moisture determination from oven or other primary method. The universal moisture meter gives fairly accurate reading of moisture content on wet basis.

electric resistance method
(II)Dielectric Method:-

Such devices measure the dielectric constant of grains. Dielectric constant is quantity measuring the ability of a substance to store electrical energy in an electric field. Grains are filled in chamber. The sides of the chamber are formed by the plates of a condenser between which a high frequency current is passed to measure capacitance of the sample. The capacitance varies as per water present in the sample, the degree of compaction and grain temperature.

Dielectric Method
(III)Chemical method:-

In this method water is removed by adding a chemical which decompose or combines with water. From the chemical reaction a gas is produced which can be measured volumetrically or which decrease the original weight of sample. This method is used for determining the moisture content of forages and grains by shaking an excess of calcium carbide with 30 grams of material. About 10-25 minutes are required to reaction.

chemical Method

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