The Raw Material and the Process

THE RAW MATERIAL AND THE PROCESS

Food processing is seasonal in nature, both in the demand for its out output and in the availability of its raw materials. In common with any other manufacturer the food processor would prefer his raw materials: to be continuously available in sufficient quality and quantity; to enable him to operate on a planned year-round basis; to be stable in storage; to be of uniform characteristics and to be of predictable prices.

In general, the process suitability (S) of a food raw material is determined by a balanced assessment of its properties such as: its availability (a); its geometric (g), physical (p), functional (f), growth (gr) and mechanical (m) properties and its thermal (t) and electrical characteristics (e), etc.

S = (a+g+p+f+gr+m+t+e+…)

The relative importance of these factors in their contribution to the suitability index will, of course, vary depending on the raw materials, the process applied to it and the end product made from it. Properties of major importance in the selection of food raw materials are:

(i) Geometric properties - shape, shape uniformity, freedom from surface irregularities, unit size, unit weight.

(ii) Other physical products - colour, texture, aero- and hydro-dynamic characteristics, frictional and surface properties.

(iii) functional properties - flavor, stress resistance, defect level, processability

(iv) Growth properties - growth and maturation characteristics.

1.1 Geometric Properties Of The Food

Foods of regular geometry are best suited to high speed mechanized processes. Potato varieties of smooth shape and with shallow eyes are preferred for mechanical peeling and washing. Again, smooth skinned tomato varieties are more easily washed than ribbed varieties (which also tend to harbor insects such as Drosophila). Shape

The dimensional relationships of food unit are important: in packaging; in controlling fill-in weight; in freezing, in canning and other heat processes; and in determining the way in which materials behave during pneumatic conveying and bulk storage.

Uniformity of Shape

This is of importance during filling into containers; conveying; heat treatment; freezing; dehydration; and during sorting/ and grading operations.

The roundness of biscuits and hamburgers; the sphericity of apples or potatoes; pears which are of uniform perform shape and cucumbers of regular uniform shape are examples of desirable shape-uniformity characteristics.

Freedom from Surface Irregularities

Cleary, surface projections and depressions occurring in a food unit present cleaning and processing problems.

Size and Weight of Food Units

Optimum dimensions exist for each process and raw materials complying with these specifications must be provided. Whilst sorting can assist in size and weight control, raw materials containing oversize and undersize materials present the processor with economic and disposal problems. Determination of unit weight maybe carried out by the use of automatic machines or assessed by manual weighing of representatives samples. Size is important in waste control (e.g. peel- and stone-to-fruit ratios are size dependant), whilst with processes handling individual food units (e.g. peeling or skinning machines) throughout is dependent on unit size.

1.2 Other Physical Properties of Raw Materials

Many physical properties, in addition to geometric properties warrant consideration when selecting food raw materials. These include: colour; texture; frictional characteristics and surface properties.

Colour Properties In low temperature processes (e.g. freezing or freeze drying), colour changes during processing are minimal, so the colour of the raw material is reasonable index of its suitability for these processes. Some varieties of apples and pears develop a pink tinge on canning, whilst canning rhubarb and some cherry varieties become bleached due to migration of colour into canning syrups. Chlorophyll is converted into brown green phaeophytin during the heat processing of green vegetables. Colour control is best exercised by selecting varieties of known processing performance, by using the correct pretreatment procedures such as blanching and using process conditions designed to retain the natural food colour.

Textural Properties

The textural characteristics of the raw material are of great importance. The first requirement is that the raw material must be sufficiently robust to withstand the mechanical stresses to which it is subjected during preparative operations. Secondly, the raw material must withstand the processing conditions so as to yield a final product of the desired texture. Fruit and vegetable varieties with improved mechanical strength have been developed, such as tough skinned peaches and tomatoes suited to mechanized washing, peeling and sorting. (Flavor savor – polygalactorunase / pectin)

The evaluation of textural characteristics is based either on sensory testing using trained panels or on instrumental procedures. Differences in these properties between the desired and undesired parts of a raw material may be used to clean, sort and grade the raw material. Air and water are frequently used to convey, mix and process materials.

Frictional Properties

Before grain can slide down a chute or discharge from a bulk bin the forces of static friction due to inter particle action and particle-wall friction must be overcome. Once material begins to flow, the coefficient of dynamic friction must be exceeded in order that flow should continue. The friction properties of food materials thus play an important part: in gravity and pneumatic conveying; in flow into and discharge from bulk storage vessels and n mixing operations. Differences n frictional properties maybe used to effect separation of contaminants in cleaning processes and to sort put blemished or damaged units from sound material.

Specific Surface of Food Units This raw material property is important in processes involving gas/solid and liquid/solid reactions as respiration, extraction, smoking, bringing and oxidation. It is also an important economic factor in determining peel and core to fruit or vegetable ratios and washing losses. The specific surface properties of particulate foods are also of importance in fluidized processing and movement and in other surface-sensitive phenomena such as: contaminant retention; cleaning; radiant energy transfer (infra-red, dielectric and microwave heating) and in aero - and hydrodynamic transfer. Surface area may be determined by peeling followed by measurement of the peel area using a planimeter - a measuring instrument used to determine the area of an arbitrary two-dimensional shape

1.3 Functional Properties of Food Raw Materials

A raw material of ideal functionality is one which may be processed to give a first quality product whilst permitting maximum process effectiveness. The functional properties required of material will vary depending upon the process to which it is subjected. Many examples of varieties developed for special purpose are common knowledge, e. g sheep bred for wool or meat and cattle for meat and milk. Special wheat varieties yield soft, low protein flour suitable for biscuits and cakes whilst other high protein wheat’s are used for bread flours.

Flavor Properties

Flavor, perhaps more than any other property, is a matter of personal preference. In serving a mass market, extremes of flavor must be avoided. In some cases, the flavor often processed food is more of a function of additives than of raw material. Examples of this are the use of strongly flavoured syrups in some canned fruits and of protein hydrolysates and yeast extracts in meat soups. For these reasons, flavor is of less importance than other factors (e.g. colour and texture) in determining the suitability of a variety of processing.

Resistance to Processing Stresses

Some dessert varieties lose their rigidity on processing and are, therefore, unsuitable. Clingstone peaches have excellent texture when canned. For this reason this variety is used almost exclusively, in preference to the better flavoured but more delicate freestone and white peach varieties.

Freedom from Defects Food manufacture unfortunately, is a low profit activity, and based as it is on raw materials of natural origin, these representing a major cost factor, it is vital to procure low defect-level input materials. Cleaning, sorting and grading generate labour and plant costs and may cause product damage, producing material defects. These preparatory procedures are essential steps in processing but the plant used must be carefully designed and the operators thoroughly trained if defect levels are to be controlled. The combined effect of these defect-producing activities is evidenced by the large output of waste from most food factories. Defects which affect processing suitability include the following:

(i) Geometric deformities and inequalities

(ii) Mechanical damage due to impact, puncture or abrasion.

(iii) Colour defects

(iv) Insect, animal, fungal and microbial damage.

(v) Extraneous matter contamination.

(vi) Textural and functional defects.

(vii) Immaturity or over-maturity.

1.4 Growth properties of the raw material

The processor is getting involved in many aspects formerly the concern of the supplier, such as contract buying, growth programming, transportation and storage.

Contract Purchasing Of Raw Materials

Purchasing of raw material produce in the open market is substantially outmoded. These days the food processor contracts ahead with the farmer or grower for a definite acreage of produce. Under this system the processor may do any or all of the following:

(i) Agree the sowing plan

(ii) Supply seed of selected varieties, fertilizer and sprays.

(iii) Indicate expected harvest date.

(iv) Provide technical advice via his field men. (v) Provide harvesting or vinning equipment and, sometimes, labour.

(vi) Arrange or provide transport keyed to his production and handling systems.

This system is applied to an ever growing list of food raw materials from wheat, barley and rye, to vegetables such as potatoes, peas and beans. It is a most effective method of assuring suppliers of the required materials at the required time and in the required quantity.

Selective Breeding of Raw Materials

The development of suitable varieties for processing requires close cooperation between breeders, research stations and processors and considerable progress has been made. Selective breeding of processing raw materials is now commonplace. Typical examples include: high dry matter content potatoes, tomatoes and onions, tomatoes giving puree of improved colour and flavor; Brussels sprouts of improved freezing properties; and bitter-free cucumber varieties.

Maturation Properties

The maturity of raw material is important in controlling both the quality of the final product and the effectiveness of processing. Processing varieties are required to mature both uniformly (to facilitate mechanical harvesting) and predictably, to permit adequate planning. Over maturity results in a proportion of reject material, excessive product damage and spoilage during storage. Sterilization efficiency may be reduced due to the high microbiological loads often encountered with over-mature materials. Under maturity implies a reduced yield and the final product is liable to have sub-standard colour, flavor and texture. In some foods (e.g. meat, cheese, wines), a period of maturing is essential whilst, in others (e.g. eggs), maturing is undesirable. Fruits and vegetables may be harvested over a range of maturities, depending on their destined end-use.

Prediction of Maturity

Forecasting of harvest dates is of great a value to the planner. In many commodities (e.g. meat, milk, eggs), harvest patterns are wells established. Armed with specific growth data on the variety of crop and knowledge of the average metrological records of the growing area, it is possible to make a long-range forecast of the probable harvest date for any sowing. Corrections can then be made, during the growing period, for the actual weather conditions and the long range forecast may be adjusted accordingly. Extension of Harvest Season

The use of early, middle and late varieties has done much to spread the season over which food raw materials become available for processing. The widespread adoption of the broiler and battery systems has extended the availability of chicken meat and eggs. Availability may be extended by using preserved raw materials such as brined, dried and pulped crops or by sorting part-processes of raw foods. Usually, increased costs are incurred with these procedures and their economic feasibility must be considered carefully before adoption.

Mechanization and the Raw Material

The food industry, faced with soaring labour costs and low profitability has mechanized its operations wherever practicable. Mechanization, whilst offering undoubted advantages, unless carefully engineered, can cause excessive product damage.

Product Damage

The main causes of damage during food preparation are: operator damage caused by careless manipulation; unsuitable mechanical handling procedures; poor equipment design and incorrect containerization.

Damage manifests itself in many ways: the appearance of the food is affected; mould and rot infections invade bruised and punctured areas; infestation by insects and vermin occurs and enzymic and chemical spoilage is accelerated. Damage spoilage spreads to adjacent material causing financial loss and impairment or invalidation of process effectiveness. In the extreme this represents a positive health hazard.

Produce is damaged: by impact with other produce or hard surfaces; by excessive pressure caused by overlying food; by puncturing by sharp projections and by abrasion caused by movement and vibration.

Mechanical Harvesting

The change from selective to mechanical harvesting of the “once-over” or destructive type has produced substantial reductions in labour costs but has many disadvantages. Amongst the more important of these are excessive damage and consequent quality reduction and increased capital investment and maintenance costs. Currently, mechanical harvesting machines utilize one or more of the following seven principles: (i) Shaking of trees or bushes carrying crops (sometimes used in conjunction with abscission promoting sprays)

(ii) Combining of berry fruits such as blueberries and strawberries.

(iii) Cutting of cabbages, lettuces, cauliflowers, etc., the plant being served at ground level.

(iv) Pulling of carrots, radishes and celery in which the stems are gripped by opposing, driven belts.

(v) Stripping of cucumbers and maize ears using differentially driven soft rubber rollers.

(vi) Vinning of peas and beans involving either stripping, pulling or cutting of the vines followed by podding.

(vii) Mechanical digging of root crops such as potatoes and onions.

Frequently, harvesting machines carry out other preparative operations such as aspiration, screening, destining and colour sorting.

Mechanical harvesting therefore requires a multi-disciplinary approach with breeders, farmers, food technologists, engineers and economists working in close cooperation.

Design of Transit Containers for Raw Materials

In transit damage due to impact, abrasion and pressure, frequently is the result of incorrect containerization. Consideration must be given to other factors such as: the type and variety of fruit; its maturity; its shape, its size (as affecting its kinetic energy when falling) and nature of the container surface. (e.g. its hardness and texture). Pressure damage caused by overlying material in containers which are too deep or by overfilling of open top containers which are then stacked is all too common. Some apples will not withstand an overlying static weight in excess of 4kg whilst peaches are given more fragile. Pressure damage is cumulative, a pyramid of damage emanating from the original pressure point.

Transportation of Raw Materials

Arranging to have available raw materials of the proper quality in their required amounts and at the correct time is mandatory to any process. Raw foods sensitive to microbiological, insect and chemical spoilage and, in many cases, still continuing to respire, become available over a relatively short period at harvest. Proper scheduling is vital and the processor should either specify delivery procedures in the buying contract ( including a penalty clause in the event of default) or, alternatively, exclude delivery from the supplier’s liability and accept responsibility for transport himself.

Particular care must be exercised in the correct choice of container and maintaining these in a sound and clean condition so as to avoid contamination of the raw material with wood fragments, nails, etc. where transportation takes place in bags or sacks, careful sack cleaning and examination is necessary. Second-hand sacks which may have contained fertilizers or spray materials are sometimes pressed into service in an emergency, occasionally with dire consequences. Transportation vehicles require special attention. Above all, vehicles should be thoroughly clean and insect free. Contract transport is notoriously difficult to control in these respects and, all too frequently, outbreaks of insect infestation are traceable to foods being transported in a vehicle which has been incompletely cleaned after carrying infested material for another customer.

Raw Material Storage

Ideally all raw materials are processed immediately on arrival at the factory. In practice this situation seldom exists so that some provision must be made for on-site storage of raw materials and part-processed products. In this away, delivery delays, plant breakdowns and bumper harvests may e accommodated and, occasionally, the store can be an asset allowing forward-buying when advantageous market conditions exist.