Determination of moisture content by oven drying method.
Title:
Determination of moisture content by oven drying method.
Objective:
To determine the moisture content of the given samples by oven dry method.
Need and scope of the experiment:
All food grains, when harvested early contain some amount of moisture. To store these grains safely for longer period, moisture content need to be reduced to a safe storage level by drying. During drying, observations of grain moisture at specific time interval are needed to understand the drying behavior.
Definition:
The water content in any food sample is called moisture content. The moisture content is the ratio of the weight of water to the weight of the solids in a given mass of grains/food. This ratio is usually expressed as percentage. Moisture content is expressed in % wet basis and % dry basis.
- The moisture content, m, % wet basis is
m = [Wm/(Wm + Wd)] X 100
Where, Wm=Weight of moisture (g)
Wd= Weight of bone dry material (g)
2. The moisture content, M, per cent, dry basis is
M = (Wm/Wd) X 100
Where, Wm=Weight of moisture
Wd= Weight of bone dry material
Relation between % wet basis moisture content and % dry basis moisture content is
M = [m/(100-m)] X 100
Materials and Apparatus Required:
- Grain sample
- Glass petri plate or metal container
- Hot air oven
- Desiccator
- Weighing balance
Moisture content determination methods:
Moisture content can be determined by direct methods and indirect methods.
Direct Methods:
These methods are simple and accurate and mainly used for research purpose but time required is more than indirect methods. Hot air oven method and Brown-Duvel distillation method are the examples of direct method.
The hot air oven method can be accomplished in a single stage method if moisture content of sample is less than 13% or by double stage method if the moisture content of sample is more than 13%.
Single stage method:
- Grind the 2-3 gram of grains.
- Keep the ground sample in hot air oven for 1 hour at 130°C.
- After 1 hour, remove the sample and place in desiccator and then weigh.
- Calculate the moisture content by above formula.
Double stage method:
- Take 25-30 gram whole grain sample and keep in hot air oven at 130°C for about 14-16 hours so that moisture content is reduced to about 13 %.
- Follow the steps given in Single stage method.
Indirect methods:
Indirect methods are based on the measurement of some properties of grain that depends upon moisture content of the grains. Some example of the indirect methods is Electrical resistance method and Dielectric method.
Procedure:
Procedure for determining moisture content by hot air oven method is as follows.
- Clean the container or glass petri plate and weigh it. Note this weight of empty container as W1 (gram).
- Take some grains (5-6 grams) in the container and weigh it. Note this weight of container and grains as W2 (gram).
- Keep this container in oven and heat the samples at 130°C for about 16 to 24 hours. Ensure that sample will show constant weight.
- Note this final constant weight as W3 (gram).
Determine the moisture content by given formula.
Observations:
| S.N | Sample Name | Replication 1 | Replication 2 | Replication 3 |
| 1 | Weight of container W1 g | |||
| 2 | Weight of container + grains W2 g | |||
| 3 | Weight of container +dried grains W3 g | |||
| 4 | Moisture content, %wet basis m = [(W2-W3)/(W2-W1)] * 100 |
Result:
The moisture content of the ………(write sample name here) is ……% (wet basis( and ……% (dry basis).
