ELEMENTARY MAIZE MEAL QUALITY CHECKS #1: MOISTURE CONTENT TESTING

Quality control plays an important role in every stage of the production of maize products, from intake to packing.

Large mills have fully equipped laboratories where routine quality checks are carried out. However, the small miller cannot afford to equip and run such a laboratory, and therefore needs an area in the mill where the simpler, basic tests can be carried out.

Moisture content is one of the tests that need to be conducted:

Silo/ intake

There should already be an accurate moisture meter at the silo/ intake as it’s important to test the moisture of the incoming maize. A maximum level of 13% is recommended, allowing the miller to add some water during conditioning to achieve a milling gain, while still ensuring a low moisture content in the bag when the product is packaged.

Maize conditioning

The moisture tester at the intake should also be calibrated so that moisture tests can be conducted on the conditioned maize to ensure that the moisture on the mill is correct. The oven method (see below) could also be considered.

Feed to the mill

    Maize products

    The maximum permissible moisture level of maize meal at the time of packaging may not exceed 14% in South Africa and many other African countries.

    Millers aim to get as close as possible to this level using moisture that costs virtually nothing compared to maize, but this is only achievable if the levels of the maize are not too high, as they can add very little moisture or else risk going above 14%.

    The customer on the other hand wants a product with a good shelf life, because if the moisture content is too high, the maize might go rancid or bitter – especially during the hot summer months and in areas of high humidity.

    Pneumatic conveying causes a slight level of moisture loss and mills like the Roff C-80 add extra moisture to compensate for it.

    There are various moisture testing machines available from which the miller can choose. The simplest and most accurate method of moisture testing is the oven test.
    The customer on the other hand wants a product with a good shelf life, because if the moisture content is too high, it runs the risk of going rancid or bitter – especially during the hot summer months and in areas of high humidity.
    There are various moisture testing machines available from which the miller can choose. The simplest and most accurate method of moisture testing is the oven test.

    A736957

    METHOD

    A 10g sample of meal is weighed to the nearest 1mg, and placed into a container of known weight. The container is placed into a drying oven, preheated to 130°C, and dried for two hours. The sample is removed and placed in a desiccator, and cooled for 30 - 45 minutes after which it’s weighed to the nearest mg. The moisture content is calculated as follows:


    Moisture content = Initial weight of sample in grams
    Dried mass of sample in grams

    This method can also be used to test the moisture of maize at the intake, particularly when there’s a need to check the accuracy of the moisture meter. For whole maize, the sample would have to be ground up before testing on a simple hand grinder.

    FREQUENCY OF MOISTURE TESTING

    • Silo/ intake: Every truckload of maize received
    • Conditioned maize: When conditioning the maize
    • Maize to the mill: At least twice a shift
    • Finished products: At least twice a shift

    Important: Don’t forget to check the moisture of the chop (germ), as it’s vital that it doesn’t turn rancid. Testing is particularly necessary if the germ isn’t sent to a feedlot on a daily basis.

    KEEP RECORDS OF YOUR TESTS

    It’s recommended that millers keep records for each type of test done in the mill, so that customer and other complaints can be traced back to the date of manufacture.

    A simple way of recording the results is to add a section on to the extraction logbook. The miller notes the time of the test, the product and the results obtained. If the results are entered into a computer, the same method of recording will apply. 

    MUST-HAVE LABORATORY EQUIPMENT

    • Good quality moisture tester
    • Electronic laboratory scale
    • Stainless steel table to work on (or table with a smooth surface)
    • Perspex spec measurer
    • Laboratory sifter (set of hand screens with critical sizes in a small mill)
    • Small oven that can heat to 160°C
    • Hand grinder or coffee mill

    A736854

     

    Maize mealMaize millingMaize milling machineProduct quality checkProfitable business

    Leave a comment

    All comments are moderated before being published