Wheat Crisps – Extrusion Cooking Technology

These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

1 Emphasis On Environmental And Safety Aspects

• During cutting the extrudates splinters of the rotating knives may get into the product

• high energy input.

• Spelt wheatspelt wheat is known as organic grown grain, as manuring is not possible.

2 Introduction 1. Introduction

Spelt wheat is an ancient and under-utilized crop. As only wheat, rice and corn are of general interest worldwide the aim is the production of spelt wheat crisps for further use in granola bars. The texture , the bulk density and the expansion index of the extruded material will be measured.

Times of overproduction and environmental problems remind people of less productive but ecological beneficial crops. Furthermore they increase the interest in healthy nutrition and in food cultivated and produced without fertilizers or plant-protective agents.

Spelt wheat is ancient wheat covered with husks and able to grow even in colder climates and on poorer soils. But due to more difficult cultivation and processing, spelt wheat still remains a cereal for speciality products – though it was the main crop in Central Europe over centuries. Spelt wheat originates from South-west Asia; there it was developed from Emmer, which is a tetraploide wheat and Aegilops squarrosa, a wheat related grass variety. Following the Danube it found its way to Central Europe. A change in climate favoured the cultivation of spelt wheat above the two other mentioned cereals.

During the last years environmental and economical problems of agriculture as well as the increasing demand for healthy food in industrial countries, caused a revival of spelt wheat as this cereal has some mentionable characteristics in chemical composition, besides the agricultural beneficial aspects of robustness, modesty and the hull, protecting against pollution or infections.

Extrusion cooking is an effective and economic continuous process in which the physical, nutritional, and sensory properties of the raw material can be changed to a desired degree. Positive effects include increased digestibility, destruction of anti-nutritional constituents, toxic substances and micro-organisms.

The responding factors texture , bulk density and expansion index are dependent on the raw materials used and the configuration of the extrusion cooker. As only spelt wheat flour is used, the influence of the raw material cannot be calculated or compared to other flours and mixtures.

Starch and similar components like maltodextrines are responsible for higher expansion indices and lower bulk density while components like fat , sugar and salt have the contrary effect. Regarding the formation of water vapour during the discharge of the molten material through the dies the water content in the flour and water addition have the greatest influence on the expansion.

The influence of the configuration of the extruder on the product is more complex but in general the geometry of the screws, the temperature profile and the diameter of the dies have the greatest effect.

Mass temperature and mass pressure in the extruder depend on both – raw material and configuration of the equipment.

3 Apparatus And Materials

3.1 Apparatus

• Pin mill – Pallmann.

• Extrusion cooker – Cincinnati Milacron: the used extrusion cooker is a conical counter rotating twin-screw extruder with four temperature zones, which can be adjusted separately.

• The configuration of the extruder is:

• Temperature zone 1: 70°C.

• Temperature zone 2: 100°C.

• Temperature zone 3: 130°C.

• Temperature zone 4: 160°C.

• Temperature of the screws: 70°C.

• Speed of the screws: 80 rpm.

• Screw type: 300 with two shearing zones.

• Die: 16×1 mm.

• Texture Analyzer TA-XT2i, Stable Micro Systems.

• Sliding caliper.

• Tubs.

• Scales.

3.2 Materials

• Spelt wheat: 20 kg.

• Water.

• PE bags.

4 Procedure

For the preparation of the raw material the hulled whole kernels have to be milled using a pin mill. The obtained flour is then filled into the hopper of the extrusion cooker.

The system has to be heated up to the adjusted temperatures and then the engine of the screws has to be started. Afterwards the dosing device and the pump for water addition are started. The gravimetric dosing has to be adjusted to a value of 30 kg h^–1, the water dosing pump has to be started with maximum flow. When the product comes out first in a line it is quite wet and knead able. Dependent on the original water content of the flour, the water addition has to be reduced until the product coming out of the extruder expands and feels dry and less compact. If the water content in the flour is higher than 12 %, no water addition is necessary. At this time the pelletizing head can be closed and started.

The obtained extruded material must be cooled for about 2 h and then can be packed or used in the mixture of granola bars. Figure 18.1 shows the scheme of the used extrusion cooker.

Figure 18.1.

Scheme of the extrusion cooker.

In Figure 18.2 the flow chart of the extrusion process is shown.

Figure 18.2.

Flow chart of the extrusion process.

4.1 Analysis

4.1.1 Bulk Density

Tubs for measurement of the volume and scales for the weight are used. The tub is filled with extrudates and the weight is determined. The bulk density has to be expressed as g l^{– 1} using eq. 18.1.

$${\text{bulk density }} = \frac{{\text{weight[g]}}}{{\text{volume [l]}}}$$

((18.1))

Weight: 783 g in 5 l.

4.1.2 Expansion Index

A sliding caliper is used to determine the diameter of extruded material and diameter of the die. The result is a dimensionless value calculated as shown in eq. 18.2.

$${\text{expansion index}} = \frac{{\text{diameterof the extrudates}}}{{\text{diameter of the die}}}$$

((18.2))

• Diameter of the die: 1 mm.

• Diameter of the extrudates: 4.3 mm.

In Figure 18.3, examples (a) and (b) of two different samples are shown.

Figure 18.3.

(a) Sample A and (b) Sample B.

5 Data Analysis And Questions

• (a) On which parameters is the expansion of the extruded material dependant ?

• (b) Why is the temperature in the first temperature zone lower than in the fourth ?

• (c) Which kinds of forces are occurring in the extruder ?

• (d) What can the number of peaks in texture measurement tell you about crispness ?

• (e) In Figure 18.3, what is the difference between (a) and (b) regarding crispness and maximum force ?

• (f) Please calculate the bulk density and the expansion index of the obtained extruded material (Table 18.1).

• (g) On which parameters is the expansion of the extruded material dependant ?

• (h) Why is the temperature in the first temperature zone lower than in the fourth ?

• (i) Which kinds of forces are occurring in the extruder ?

• (j) What can the number of peaks in texture measurement tell you about crispness ?

Figure 18.4.

Extrusion cooker.