Objectives of quality control in milling

22 April 201910 min reading

“Quality control represents the first line technical assistance and problem solving function. It is important to have good internal specifications and quality control must see to those specific characteristics critical to the quality and function of the product and at the same time take into account the economics. Quality control must be involved with the life cycle of the product to follow it through the channels to the customer.”

Ronald Sebastian Milling Technologist Mechanical Specialist Consultant Morning Star Milling Corporation-Manila Quality control is not just a laboratory function, but is the responsibility of all departments concerned in flour production, e.g. wheat procurement, silo operation, screensroom, milling, packing, warehouse, logistics and management.

All these departments are concerned with quality requirements, while the laboratory is the connecting link between them, in terms of numbers and results which are an indication of the efficiency of the various departments.

It is important that everyone concerned in quality control receive sound training on the particular aspects for which they are responsible. Where ever sampling is done or test apparatus is used, no person should be allowed to sample or use the items without first being trained on exactly how the item functions and how to interpret the results obtained. All training must include basic principles as well as objectives. Where scientific apparatus is used, the training must be undertaken by the senior of the laboratory. All laboratory assistants must be given a training program from the start of their employment. This is the responsibility of the laboratory manager and his/ her, deputy or supervisor. The trainee must learn the specifications for each product and the reaction to unsatisfactory results, how to work out and correctly interpret the results and the necessary records to be kept, (and the reasons for this) including data which will identify the samples.

Safety factors must be emphasized and safety equipment made available and used. Trainees must also learn the importance of good housekeeping including cleanliness and that accuracy can be adversely affected if instruments are not used in, or left in a clean and orderly state.

Laboratory tests are carried out under strictly controlled conditions and the results are expressed in empirical terms. Any deviation from these conditions, e.g. temperature, time, acidity, etc. would give a different result.

Fortunately, most methods used in the milling industry, have universal applications and are carried out under the same controlled conditions, although the results are still dependent on the skill of the operators. Some methods, such as moisture tests, do not have a set procedure. The test (oven) can be carried out, using the same equipment, but different sets of conditions for time and temperature can produce different results.

While the use of a particular set of conditions may not affect moisture control in the mill, it could be important where a buyer carries out his own tests, using a different set of conditions and has supplied, or been supplied with a moisture specification. This could also apply to other specifications, such as, water absorption and physical dough tests. Although these tests are carried out under controlled conditions, mechanical differences often occur between different sets of apparatus. It is therefore important that the buyer and the seller agree that such differences can and will be taken into account.

What is quality control and how does it fit into the system? The feedback must come from the sales department whether the product good or is it bad. Quality control represents the first line technical assistance and problem solving function. It is important to have good internal specifications and quality control must see to those specific characteristics critical to the quality and function of the product and at the same time take into account the economics. Quality control must be involved with the life cycle of the product to follow it through the channels to the customer.

Quality control must report any product that does not meet the specifications. The manager must take the position of the customer and decide whether the consumer will be receiving value for his money. This must also be taken with the overall cost of production and cost of raw materials and the quality specifications of the raw materials at the time of production, as the quality of the raw material may not be consistent with the mills requirements for certain products.

Most modern mills employ a research and development department, who are responsible for taking note of any variances in the quality parameters of the raw materials and advise changes to extraction values and amend production specifications to suit. They are also responsible for making changes to the mixing and blending recipes to suit the wheat characteristics when deviations are negative.

Objectives of hygiene To ensure safety and purity of all products, for all precautions to exclude foreign matter. Cleaning schedules for premises, equipment, staff and all vehicles used in distribution. Education in food hygiene, personal hygiene and equipment cleaning. Rodent, insect and bird control. Advising on suitable cleaning equipment, materials and detergents.

Hygiene rule: 1. Wear clean overalls (uniforms) and head coverings. Top pockets and loose hanging clothing not permitted. 2. Wash hands before starting work, after every break and always after visiting the toilets. 3. Cuts and wounds must be covered with approved dressing. 4. Keep working area clean, neat and tidy at all times.

RAW MATERIALS Silo: In addition to taking in the wheat and arranging the storage system, the silo operator is responsible for preliminary inspection of all consignments and in addition, the important job of sampling. The importance of using the appropriate sampling equipment and exercising the sampling procedures for each load of a consignment. Batches of grain are rarely uniform in quality even when regarded as acceptable. Pests usually occur non-randomly in stored grain. Consequently the only sure way of obtaining complete and accurate information about the grain is to carry out a total examination. This may be possible if the quantity to be examined is small, but is usually neither practical nor economical when a large quantity is involved. The choice is either not to examine the consignment at all or to take samples to obtain some information, acknowledging that anything less than a total examination is bound to affect the accuracy of the results.

Principles of representative sampling The results of sample analyses can be expressed in precise terms. However, precise analytical results may be of little practical value, and may be misleading if the samples are obtained without taking into account the non-random or aggregated distributions of foreign matter, damaged grains, insects, etc.

Certain principles of representative sampling must be observed: • The consignment should be divided into primary units of equal size or status, which may be sampled. For bagged grain, each bag may be regarded as a primary unit. For bulk grain, the primary unit may be expressed in terms of weight, if the grain is being moved, or volume, when it is static - as in a truck or bin. • All primary units should have an equal opportunity of being sampled. This is possible only during the construction or dismantling of a stack, the loading or offloading of a truck, or when bulk grain is being moved. • The method should select, without bias, a representative number of primary units from the consignment. Many countries adopt the recommendations of ISO 950 “Cereals - Sampling (as grain)”.

Double-tube sampling spears These spears comprise two metal tubes, one fitting closely inside the other and each with several common slots. Spears may vary in length from 45cm to 3.5m, and in width from 12mm to 50mm. turning the inner tube through 180° opens or closes the intake apertures, and so collects grain from a transverse section of the container.

Double-tube sampling spears are designed primarily for obtaining samples from vertical lines of penetration in bulk grain, although small versions may be used for sampling bagged grain. They are superior in many ways to the simple bag sampling spear, but are still instruments of haphazard rather than representative sampling.

Equipment for obtaining primary samples from bulk grain Bulk grain is sampled either when it is static, i.e. when it is contained in a truck, barge or storage bin, or when it is on the move, i.e. when it is being discharged through a spout or on a conveyor belt. A wide range of sampling equipment has been developed to meet the special requirements of these various situations, some for small-scale operations and other items for situations where grain is handled in very large quantities.

Double-tube sampling spears Spears 1.8m long and 3.5cm outer diameter are commonly used, but longer 3.7m double-tube spears are available for sampling grain in exceptionally deep trucks and barges.

The sampling spear should always be inserted into bulk grain at a slight angle from the vertical, with the slots facing upward. The slots must be opened only when the spear has reached the sampling position, and must be closed before it is removed.

Manually-operated deep bin probes The simplest probe of this type consists of a hollow spear head, which serves as a sample cup, with a spring-loaded cap attached to a metal or wooden rod about 1 meter long. Extension rods are attached to increase the depth of penetration. When the sampling point has been reached a slight upward pull on the rod lifts the cap of the spear head, allowing grain to fill the cup. The probe is then withdrawn completely and the sample removed. A single probe yields up to 300g of sample material.

The deep bin fin-probe consists of a double-tube sampler with a set of extension rods. When the sampling position is reached a twist of the extension rod opens the sample intakes. This action is facilitated by the fin which prevents the outer tube from turning. A reverse twist closes the sample intakes before the probe is withdrawn from the grain. Up to 600g of sample representing a 1.5m long vertical ‘cut’ may be obtained.

A considerable amount of physical effort is required to push any of these probes into grain. None can be expected to penetrate more than approximately 5 meters.

Pneumatic grain samplers Pneumatic grain samplers overcome the main disadvantages of manual operation by using powered-suction to penetrate the static bulk of grain, and by taking a continuous sample. They are quicker to operate than manual samplers, and can be used easily to obtain samples from the sides and floors of bulk grain containers.

Working sample size In practice, it is necessary to compromise between what is theoretically attainable and the natural desire to obtain results of analyses as quickly as possible. Providing the associated margins of error are recognised and accepted, it is generally suggested that working samples of between 500 and 1000 grains should be used for the determination of common defects such as insect damage, broken grains and discoloured grains. Equivalent minimum working sample weights are:

Samples of these sizes can be analysed in 10 to 20 minutes, depending upon the skill of the inspector and available equipment.

Mill Laboratory, Control in The Screens Room, Mill And The Warehouse The laboratory is the focal point of the quality control system, receiving and analyzing samples from all departments. The workload of the laboratory is determined by the size of the mill, the number and types of flour produced, whether production runs are long or short, whether speciality flours are produced and a classification system operating and, naturally, on the equipment available.

Fortunately, many of the tests required to check production, packing and bulk loading samples take a relatively short time to complete, e.g. colour grades, water absorption, falling number, chittick tests (% carbon dioxide) and spot tests.

Articles in Article Category
18 January 20217 min reading

Ensuring safety of grain in storage

Dr. Stathis Kaloudis Senior Engineer, Centaur Analytics, Inc. Centaur ...

29 November 20224 min reading

Molinera Itata: Tradition and world-class technology in oat processing