Embed Size (px)
DESCRIPTION
Most cereals contain a large amount of starch. In its natural form, the starch is insoluble, tasteless and unsuited for human consumption. To make it digestible and acceptable, it must be cooked.
Citation preview
NEXT PAGE
Grain & Feed Milling Technology is published six times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2010 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1466-3872
Digital Re-print - July | August 2011 Cooking cereals with extrusion
www.gfmt.co.uk
Most cereals contain a large amount of starch. In its natural form, the starch is insoluble,
tasteless and unsuited for human consumption. To make it digestible and acceptable, it must be cooked.
Cooking or gelatinization of starch in the traditional cereal process is controlled by time, temperature and availability or presence of water. In the extrusion cooking
process, shear is a fourth dimension that impacts product quality.
Almost any cereal can be cooked using an extruder, but if expansion is a major objective, the numbers of functional cereals
are limited to de-germed corn/grits and rice. Cereals that have high amounts of lipids are
more difficult to expand due to dough slippage within the extruder barrel. This type of cereal usually requires high moisture and high tem-perature before significant puffing will occur.
In general, starches with 5-20 percent amylase content will significantly improve expansion as well as texture of the break-fast cereals and snack foods.
An old method of cooking cereals or starchy foods is called browning or toasting and it involves cooking them by dry heat. A thin layer of grain is spread in a shallow pan and this is placed in a slow oven. After the grains have browned slightly, they are stirred and then they are permitted to brown until an even color is obtained. By this method the flavor of the cereals is developed and their digestibility increased.
Since grains keep much better after
they have been subjected to the process of toasting, this means is used extensively for preserving grains and cereal foods.
Cooking factorsHow long a cereal needs to be cooked
will depend upon several factors. The length of time to cook cereals also
varies with their kind and form, the coarse
ones requiring more time than the fine ones. Because of this fact, it is difficult to say just how much time is required to cook the numerous varieties thoroughly.
Cooking cereals with extrusion
by Mian N Riaz1 and Brian Plattner2, Food Protein Research and Development Center1 Texas A&M University, College Station, Texas 77843-2476, USA Email: [email protected] Manufacturing Company, 714 Main Street; Sabetha, Kansas 66534, USAEmail: [email protected]
Figu
re 1
: Th
erm
al t
win
-scr
ew e
xtru
der
Figure 3: RVA comparison between whole corn flour and extruded material
Figure 2: Steam injectors
Grain&feed millinG technoloGy22 | July - august 2011
FEATURE
Grain&feed millinG technoloGy July - august 2011 | 23
SABETHA, KANSAS USA 785-284-2133 [email protected]
USA BELGIUM TAIWAN BRASIL CHINA TURKEY
Inventing the new original since 1935.
Multiply extrusion capacities for small diameter aquatic feeds with patented new Wenger technology.
Multiply extrusion capacities for small diameter aquatic feeds with patented new Wenger technology.Wenger’s innovation of diverging cone screw and oblique dietechnologies brings all the benefits of extrusion to high capacitymicro aquatic feed production. These new designs result in floating and sinking small diameter aquatic feeds that are:
• produced at rates 3 to 5 times greater than previous technology. • uniform in size and shape. • on target for density and water stability.
Request details now on high capacity, profitable production ofsmall diameter feeds at [email protected].
At Wenger, we innovate to solve customer challenges.And then we do it again.
Wenger_AQ_210x147mm 5/27/11 11:17 AM Page 1
or oven whereas for human uses the method of cooking cereal may be more sophisticated and detailed. Some of the most common methods used for cereal cooking are listed here: Batch cookingConventional extrusionTwin screwSingle screw
In extrusion cooking several steps are combined in a single continuous unit, which offers several advan-
tages to cereal manufacturers, resulting in making it a more economical method than traditional cereal cooking processes.
Recently, a new twin-screw extruder called ‘Thermal Twin Extruder’ has been introduced in the market, which can cook cereals better and more efficiently.
Some of the main differences between traditional twin screw and thermal twin screw are:
Increased extruder barrel volume allows increased levels of ther-mal energy addition
Increased thermal energy reduces the level of mechanical shear required for cooking
Reduced mechanical shear results in less break-down of the starch chains
Less mechanical starch damage gives a product with reduced ‘stickiness’
The new thermal twin-screw (see Figure 1) extruder offers a unique screw profile with single flight and variable pitch. It also has a large volume steam injec-tor with 45 degree angle and screw speeds up to 700rpm (see Figure 2).
Traditional extru-sion cooking of cereal grains results in mechanical dam-age to the starch granules giving vary-ing levels of cold water soluble starch and depressed final viscosities. Figure 3 shows the RVA com-parison between whole corn flour and extruded mate-rial that has been highly sheared. The extruded sample shown in the RVA data had thermal to mechanical energy ratios of 0.25:1.
However, little difficulty will be experi-enced if it is remembered that cereals should always be allowed to cook until they can be readily crushed between the fingers, but not until they are mushy in consistency.
There are different cooking methods, which the industry can use to cook cereal grains.
The method of cooking depends on the finished product and the objectives of the cereal cooking.
For animal feeding, cooking can be done simply by heating the cereals using a toaster
Figure 4 Shows samples that have been cooked using thermal twin-screw extruder
Figure 5 Shows the results after hydrating extruded samples
Figure 6: Light microscopy of extruded samples
Energy inputs loweredWith the new thermal twin-screw cook-
ing system the specific mechanical energy inputs can be lowered dramatically when extrusion cooking cereal grains.
The cereal grains can still be completely cooked, but since the primary energy source is thermal energy the amount of starch damage is significantly reduced. Figure 4 shows samples that have been cooked using this system in which the thermal energy to mechanical energy ratio is at least 4:1 and as high as 25:1.
The starch gelatinization levels of the thermally extruded and cooked samples can be controlled from 50 to 95 percent by varying the level of direct steam injection.
Even with the high levels of gelatinization there is limited coldwater viscosity for the samples. Figure 5 shows the results after hydrating these samples.
The beakers in the photo contain sam-ples 1, 2, and 3 (shown in order from left to right). These samples were allowed to sit for one hour then gently stirred before taking the photo. The lowest cook sample gave the cloudiest water and fell apart. The highest cook sample had relatively clear water and good particle integrity. After hydration this sample was spongy and had a texture that could be pulled apart.
It is important to note that the sample held together and did not fall apart even with the addition of the mechanical agita-tion. This would indicate that the starch in sample three was well cooked. Even though sample three is highly cooked, it does not become sticky upon hydration. High levels of thermal energy do not disrupt the starch granules to the same extent as mechanical shear and therefore the product remains non-sticky even after hydration.
Light microscopeThese samples were also examined
under a light microscope (see Figure 6). The first micrograph is from the highly
sheared corn flour. As you can see there is no ordered structure in the sample, which is what one would typically expect in a highly sheared extruded sample.
Figure 6 is of sample one. The sample still has some intact and uncooked starch granules. As the amount of thermal energy to the extruder was increased for sample two, the individual granules disappeared. There is still some ordered structure, which most likely indicates intact cell walls. The final sample, sample three, has a more disrupted structure than the previous sam-ples, but there is still an ordered appear-ance to the cereal grain structure.
Grain&feed millinG technoloGy24 | July - august 2011
FEATURE
Innovations for a better world.
Bühler AG, Grain Milling, CH-9240 Uzwil, Switzerland, T +41 71 955 11 11, F +41 71 955 66 11
[email protected], www.buhlergroup.com
SORTEX A –
for premium
end products
Excellent performance
– Unchallenged throughput capacity
– Outstanding separating efficiency
High profitability
– Maximum yield on raw material
– Profitable investment,
short payback
Maximum reliability
– Top availability, maximum
operating time
– Consistently high sorting
performance for maximum
process and product safety
Unrivaled flexibility
– High throughput capacity with
minimum footprint and low space
requirement
– Intuitive, multilingual user inter-
face
Get the best out of your grain. That means maximum throughput capacity with
maximum yield in processing raw materials such as wheat, barley, rye, oat, and
rice. The SORTEX A is distinguished by its exceptional accuracy and separating
efficiency. Its sturdy design and intuitive user interface make the SORTEX A the
ideal optical sorter for the grain milling industry. For more information, please
visit www.buhlergroup.com
MSOB_A4 englisch.indd 1 14.03.2011 10:19:19
NEXT PAGEPREVIOUS PAGE
UNORMAK DEG. MAK. IML. SAN. ve TIC. LTD. StiKonya Organize Sanayi Bölgesi 7. Sokak No: 5/1Konya / TÜRKIYETel: +90 332 2391016Fax: +90 332 2391348e-mail: [email protected]: www.unormak.com.tr
AD_Unormak_210x297.indd 1 22/07/2011 16:47
PREVIOUS PAGEwww.gfmt.co.uk
LINKS• Seethefullissue• VisittheGFMTwebsite
• ContacttheGFMTTeam
• SubscribetoGFMT
A subscription magazine for the global flour & feed milling industries - first published in 1891
In this issue:
• Cultura Technologies’ MillMaster
• Greater gains from phytase through improved formulation
• Need to explain complicated software? It’s a piece of cake
August 2011
• Packaging for the future
• Taking the first step: How to help yourself and others develop the love and understanding of flour milling
• Cooking cerealswith extrusion
ThisdigitalRe-printispartoftheJuly|August2011editionofGrain&FeedMillingTechnologymagazine.Contentfromthemagazineisavailabletoviewfree-of-charge,bothasafullonlinemagazineonourwebsite,andasanarchiveofindividualfeaturesonthedocstocwebsite.Pleaseclickheretoviewourotherpublicationsonwww.docstoc.com.
Topurchaseapapercopyofthemagazine,ortosubscribetothepapereditionpleasecontactourCirculationandSubscriptionsManageronthelinkadove.
INFORMATIONFORADVERTISERS-CLICKHERE
Article reprintsAll Grain & Feed Milling Tecchnology feature articles can be re-printed as a 4 or 8 page booklets (these have been used as point of sale materials, promotional materials for shows and exhibitions etc).
If you are interested in getting this article re-printed please contact the GFMT team for more information on - Tel: +44 1242 267707 - Email: [email protected] or visit www.gfmt.co.uk/reprints
