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2 October 2003 PR 03/72

Scientists discover why biscuits crumble

A PhD student from Loughborough University has discovered why biscuits sometimes break-up after being baked. Published today in the Institute of Physics journal Measurement Science and Technology this discovery will help manufacturers work out how to make the perfect biscuit and also avoid the costly exercise of having to discard biscuits that don't meet the high demands of their customers.

Biscuits such as the ‘Rich Tea’ type sometimes develop cracks spontaneously up to a few hours after baking, making the biscuit liable to break under the application of small loads such as being packaged or transported to supermarkets. Consumers often misinterpret this as due to mishandling. Qasim Saleem and his colleagues set out to understand exactly why these cracks occur in order to help biscuit manufacturers avoid this costly phenomenon.

They used an optical technique called 'digital speckle pattern interferometry' to look at the surface of a biscuit as it cools to room temperature after baking. This technique involves illuminating the surface of an object with a laser beam, studying the scattered light this beam produces, and is sensitive enough to detect the very small deformations that evolve as a biscuit cools.

They found that as a biscuit cools down after coming out of the oven, it picks up moisture around the rim which causes the biscuit to expand while at the same time loss of moisture at the centre of the biscuit causes it to contract. This difference results in the build-up of strain and associated forces which act to pull the biscuit apart, and which ultimately can be released by developing cracks or final break-up. These cracks make the biscuit weaker than it ought to be and so very easy to break apart when handled, moved or packaged. Manufacturers currently tackle this by removing the offending products before they reach the customers, but no quality control system is perfect and so biscuits with these minor cracks often end up in packets of biscuits that reach the customer.

Qasim Saleem said, "We now have a greater understanding of why biscuits develop cracks shortly after being baked. This will help biscuit manufacturers adjust the humidity or temperature of their factory production lines to change the cooling process in such a way that the biscuits won't break up due to normal handling and hence producing the perfect biscuit".

Ends

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Notes to editors

1. Pictures available - please call David Reid - details above.

2. The paper 'A novel application of speckle interferometry for the measurement of strain distributions in semi-sweet biscuits' by Q Saleem, R D Wildman, J M Huntley and M B Whitworth is published in Measurement Science and Technology volume 14 issue 12 pp 2027-2033. It will appear online on 2nd October 2003 at http://stacks.iop.org/0957-0233/14/2027. Copies of the paper and a summary paper are available during the embargo period -please call David Reid, contact details above. The journal Measurement Science and Technology's homepage is http://www.iop.org/journals/mst.

3. This work has been funded through collaboration between the School of Mechanical and Manufacturing Engineering, Loughborough University and Campden & Chorleywood Food Research Association.

4. The Institute of Physics is a leading international professional body and learned society with over 37,000 members, which promotes the advancement and dissemination of a knowledge of and education in the science of physics, pure and applied. It has a world-wide membership and is a major international player in: scientific publishing and electronic dissemination of physics; setting professional standards for physicists and awarding professional qualifications; promoting physics through scientific conferences, education and science policy advice.

5. The Institute is a member of the Science Council, and a nominated body of the Engineering Council. The Institute works in collaboration with national physical societies and plays an important role in transnational societies such as the European Physical Society and represents British and Irish physicists in international organisations. In Great Britain and Ireland the Institute is active in providing support for physicists in all professions and careers, encouraging physics research and its applications, providing support for physics in schools, colleges and universities, influencing government and informing public debate.

6. Loughborough has an established reputation for excellence in teaching and research, strong links with industry, and unrivalled sporting achievement. Assessments of teaching quality by the Quality Assurance Agency place Loughborough in the top flight of UK universities, and industry highlights Loughborough in its top five for graduate recruitment. Around 30% of the University’s income is for research. The University has been awarded four Queen’s Anniversary Prizes: for its collaboration with aerospace and automotive companies such as BAE Systems, Ford and Rolls Royce; for its work in developing countries; for pioneering research in optical engineering; and for its world-leading role in sports research, education and development.

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