How to Determine the Moisture Content in Paddy?

Moisture content, as we define it, is the weight of water in rice or paddy expressed in percentage. In post-harvest handling, MC is stated on a wet basis (MCwb). Simply put, it’s percentage of water in a wet grain.

The importance of measuring moisture content

It’s imperative to determine accurate moisture content. This is done with a view to effectively manage and market paddy, for each purpose requires different moisture content.

For e.g. 18% MC for storing grains up-to 2 weeks, 9% for long-term storage, etc.

Inaccurate moisture testing could lead to:

  1. Grain loss if excessively dried
  2. Increased drying costs and paddy loss if milled at high moisture content
  3. Lower head rice, when milled at wrong moisture content
  4. Weight loss when dried excessively
  5. Mold development
  6. Heat buildup in the grain
  7. Pest infestation
  8. Discoloration
  9. Reduced yield
  10. Loss of germination

How to measure paddy moisture content?

There are two widely used methods to measure moisture content. These are:

1. Primary Method: It is based on weight measurements and is ramified into 2 steps:
– Oven method
– Infrared method
2. Secondary Method: It involves measuring the electrical traits of grains using an electronic instrument

There are a number of different portable moisture meters available in the market. One simply has to make sure that the chosen meter is suitable for harvesting paddy or grains to be milled, depending on whatever you’re planning to do.

Let’s take a look at the moisture content required for different post-production activities:

Paddy Harvesting

When harvesting paddy, one needs to keep in mind that lower moisture content can possibly lead to grain shattering and higher moisture content can lead to losses owing to poor grain quality.
– Ideal moisture content: 20-25%
– Primary losses: Grain shattering and poor quality

Paddy Threshing
– Ideal moisture content: 20% for manual threshing and 20-25% for mechanical threshing
– Primary losses: Breakage/cracking, grain damage and partial threshing

Paddy Drying

The drying process should begin within 24 hours of harvest. Otherwise, there’s a very high possibility of quality deterioration and grain damage.

It should also be noted that seeds should be dried well below 12% moisture content while grains to below 14%.
– Ideal moisture content: 14% or lower
– Primary losses: Discoloration, spoilage and fungal infestation

Rice Storage
– Ideal moisture content:
14% or less if it’s to be milled or stored or a month
Less than 13% for storage up-to 12 months
12% for seed storage
– Primary losses: Pest infestation, fungal infection, loss of germination, etc.

Rice Milling
– Ideal moisture content: 13-14%
– Primary losses: Cracking and breakage

I sincerely hope this post would be helpful to all those planning to venture into the business of rice processing and milling. For any further assistance, feel free to contact Nextech Agri Solutions, one of the best rice mill consultants in India.

Paddy Drying Process In Rice Mills

At the time of harvest, the moisture content of the rice grains ranges between 18 -25%. Post the harvest, the most critical operation is paddy drying. Drying reduces the moisture content in the grain which is a requisite if it is to be stored. Delaying the drying process or drying it unevenly would result in a qualitative loss. Storing moist grains generally leads to grain discolouration or induces mold development. It further escalates the chances of pest attacks, regardless of the storage facility used. Higher moisture content also decreases the germination rate of rice seeds. The moisture should be further reduced if grains are to be stored for a longer duration.

Before starting with the drying process, certain guidelines need to be followed. The grains should be cleaned so as to avoid uneven drying and wet spots. Grains should be dried immediately after the harvest. Depending upon the storage duration, a certain level of moisture content should be maintained.
– 18% for a maximum of 2 weeks
– 14% or less if it’s to be stored for a month/if it is to be milled
– 13% or less if it’s to be stored for 8-12 months
– 9% or less for long-term storage

Grains with different moisture content should not be mixed if cracking is to be avoided.

The drying process involves different methods. Each method has its own elementary advantages and disadvantages.

1. Sun Drying: It is still a preferred technique in many parts of the world mainly because of its low cost. This method, however, is labour-intensive and should not be adopted if you plan to mill the grains.
2. Field Drying: This involves cutting rice panicles in the fields and stacking them into racks and piles. This method sometimes causes a massive heat build-up within the stacks and deteriorates the grains rapidly.
3. In-Store Drying: Grains with moisture content below 18% are dried slowly inside storage bins. These bins are equipped with aeration components and pre-heated air. It controls the humidity level of the air. It is a slow and gentle drying process and takes from days to weeks.
4. Heated Air Drying: This technique involves high temperatures to rapidly dry the grains. It can be stalled whenever the desired moisture content is achieved. It can be further ramified into 3 categories:
4a. Batch Dryer: Used by farmers and small rice millers, this is a labour intensive method and leads to uneven drying.
4b. Re-Circulating Batch Dryer: This is put to use by commercial rice millers and cooperatives. It requires moderate capital investment.
4c. Continuous Flow Dryer: Generally used by large commercial facilities.

The Process Of Making Parboiled Rice

Everyone in the country knows what white rice or a brown rice is. However the awareness about parboiled rice is very limited. So it often happens that you are asked about what is parboiled rice when you tell someone that you consume this third of the many breeds of Rice. In simple terms, Parboiled Rice means the type of rice which is partially boiled. But boiled where? The grain is simmered in the husk.

Since the process of parboiling involves three major steps which are soaking, steaming, and drying, the other name of the grain is ‘soaking rice’. As mentioned, the first and foremost process involves drenching of the grain. The act is carried out by transferring the rice into the soaking tank, setting the machine temperature at 20-30 degree Celsius and leaving the grain for 36-48 hours as per the need of the situation. Once the drenching part is done, the rice is then shifted for steaming process which requires heating up the grain for making the grain harder. The procedure isn’t much time consuming as it depends on the manufacturer what kind of grain color he or she wants to attain considering the higher the heating temperature, the lesser the processing time. Although, steaming at high temperature increases the chances of grain getting darker in color.

The final act involves drying the grain. It must be noted that withering the grain in huge quantity isn’t easy. Especially in the case when the rice are parboiled. So, the grains are sun-baked with the help of a large number of workers who have to work actively and are required to timely turn and mix the rice. Approximately 20-40% of moisture gets reduced in the initial stage of drying while the remaining percentage later.

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Different Paddy Parboiling Methods in India

Parboiling involves partial cooking of rice paddy, and soaking, gelatinizing, and drying before milling. The main objective of parboiling is to impart hardness to the grain (without hampering the husk) so that the grain can withstand the milling operations. The paddy is parboiled in the hull to soften the kernel so that the surface starch, bran, and other components can blend. After this, the water from the rice is drained and the rice is dried with steam. The dried rice then undergoes machinery procedures to polish the kernels and remove the hull.

There are three different types of Paddy Parboiling methods in India, namely:

  1. Single-staged parboiling system which is meant for small grain and boiled cream-colored rice

  2. Two-staged parboiling system which is meant for small grain, boiled and steamed white-colored rice

  3. Three-staged parboiling system which is meant for long grain rice like Basmati, etc.

A quick synopsis of Paddy Parboiling Methods in India

The raw paddy is first cleaned and then transferred to the soaking tank paddy storage bin. The raw paddy (only if its grain is long or of medium size) is then steamed for two to four minutes which is followed by the moving of processed paddy to the soaking tanks.

When the rice is in paddy form, it is soaked in water at an ambient temperature of 20-30°C and takes 36 – 48 hours to reach the requisite moisture content of 30%. On the other hand, if the paddy is soaked at a temperature of 60-65°C (hot water soaking), it reaches the moisture level in a mere two to four hours. One advantage of hot water soaking is that it reduces the steaming time which completes the parboiling process, quickly.

The smell, color, taste, and the solubility of the components of rice depends on the water temperature and the duration for which it is soaked in the water. The timing must also not be too long and the temperature also must not be too high otherwise the components would dissolve in water, the seeds would start germinating, and starch fermentation would occur.