The problem and its context
A key characteristic of some bread products is that the crust should be crisp eating yet at the same time the crumb is expected to be soft eating. Wrapping bread products often leads to rapid softening of the crust and so a degree of permeability is required for any packaging material.
Initially the crusty product was sold in paper bags but there were problems with a dry eating crumb. Perforated polyethylene bags were tried but the results from different suppliers were variable and often there was unwanted softening of the crust within a few hours of manufacture.
The background
In freshly baked crusty breads the main driving force for moisture loss is from product to the atmosphere. The rate at which the mois-ture is lost depends on a number of factors including the RH of the atmosphere and air movement across the products. Moisture is
lost from the crust but is replaced by that migrating from the moist crumb so that the latter become drier eating.
Impeding the loss of moisture from the product crust by wrap-ping is a convenient way to restrict moisture losses. However, the permeability of the wrapping material is a critical factor in deter-mining which of the textural properties of the bread will suffer and to what degree. An impermeable barrier will result in moisture equilibration and will help retain the soft eating crumb but will re-sult in the loss of crust crispness. A semi-permeable barrier (e.g. a perforated film) may be used to allow some loss of moisture and retain crust crispness while slowing down moisture loss from the crumb, but with longer storage times, dehydration of the product will follow (unless the atmospheric RH is very similar to that of the product).
The causes and its solution
While a number of perforated films had been supplied, each had different moisture vapour transpiration rates (commonly expressed as g/m2/24 h at 38◦C). This property of films provides a comparison and indicates how rapidly moisture might be lost from a wrapped product. With perforated films there are two factors to be consid-ered, the diameter of the perforations and their density per unit area. Thus, it is possible to have two films with the same number of holes per unit area but with the holes of different sizes and it is possible to have films with the same size of holes but different densities per unit area. Clearly, the greater the surface area of the holes, the more rapid the loss of moisture will be.
Finding the appropriate vapour transpiration rate for a given product tends to be a matter of trial and error since standard test used by film manufacturers cannot provide data for every type of food product that may be wrapped in the film.
Footnote
A perforated film with small diameter holes may be preferred in retail stores in order to prevent fragments of bread crust interfering with the checkout scanner, but this may not be the best option for preserving crust crispness for more than an hour or so.
References
Baik, M.-Y., Dickinson, L.C. and Chinachoti, P. (2002) Solid-state 13C CP/MAS NMR studies on aging of starch in white bread. Journal of Agriculture and Food Chemistry, 51, 1242–48.
Barron, L.F. (1977) The expansion of wafer and its relation to the cracking of chocolate and ‘bakers’ chocolate’ coatings. Journal of Food Technology, 12, 73–
84.
Best, D. (1995) Economic potential of frozen and refrigerated doughs and bat-ters, in Frozen and Refrigerated Dough and Batters (eds. K. Kulp, K. Lorenz and J. Brummer). American Association of Cereal Chemists Inc., St Paul, MN, pp. 1–18.
Bigg, E.K. (1963) The supercooling of water, in Proceedings of the Physical Society, London, Section B66, pp. 688–94.
Brummer, J.-M. (1995) Bread and rolls from frozen dough in Europe, in Frozen and Refrigerated Dough and Batters (eds. K. Kulp, K. Lorenz and J.
Brummer). American Association of Cereal Chemists Inc., St Paul, MN, pp. 155–66.
Butcher, G.J. and Hodge, D.G. (1984) Pastry technology: The softening of pork pie pastry during storage. FMBRA Report No. 116, CCFRA, Chipping Campden, UK.
Cauvain, S.P. (1996) The freezing and retarding of fermented doughs. CCFRA Review No. 3, CCFRA, Chipping Campden, UK.
Cauvain, S.P. (1998) Improving the control of the staling in frozen bakery prod-ucts. Trends in Food Science and Technology, 9, 56–61.
Cauvain, S.P. (2007) Dough retarding and freezing, in Technology of Breadmak-ing (eds. S.P. Cauvain and L.S. Young). Blackie Academic & Professional, London, UK, pp. 175–206.
Cauvain, S.P. and Collins, T.H. (1978) Centralised production of fermented goods for satellite in-store-bakeries and hot-bread shops. FMBRA Bulletin No. 2, CCFRA, Chipping Campden, UK, pp. 64–9.
Cauvain, S.P. and Screen, A.E. (1990) Effects of some ingredients on cake texture.
FMBRA Report No. 142, CCFRA, Chipping Campden, UK.
Chamberlain, N. and Knight, R.A. (1987) The water content of bread – background notes. FMBRA Bulletin No. 5, CCFRA, Chipping Campden, UK, pp. 179–81.
Chinachoti, P. (1998) NMR dynamics properties of water in relation to ther-mal characteristics in bread, in The Properties of Water in Foods, ISOPOW 6 (ed. D.S. Reid). Blackie Academic & Professional, London, UK, pp. 139–
159.
Cluskey, J.E., Taylor, N.W. and Senti, F.R. (1959) Relation of the rigidity of flour, starch and gluten gels to bread staling. Cereal Chemistry, 36, 236–46.
Cornford, S.J., Axford, D.W.E. and Elton, G.A.H. (1964) The elastic modulus of bread crumb in linear compression in relation to staling. Cereal Chemistry, 41, 216–29.
D’Appolonia, B.L. and Morad, M.M. (1981) Bread staling. Cereal Chemistry, 58, 186–90.
Dunn, J.A. and Bailey, C.H. (1928) Factors affecting checking in biscuits. Cereal Chemistry, 5, 395–430.
Fearn, T., Miller, A.R. and Thacker, D. (1982) Checking in cream crackers.
FMBRA Report No. 98, CCFRA, Chipping Campden, UK.
Guy, R.C.E., Hodge, D.G. and Robb, J. (1983) An examination of the phenom-ena associated with cake staling. FMBRA Report No. 107, CCFRA, Chipping Campden, UK.
Hsu, K.H., Hoseney, R.C. and Seib, P.A. (1979) Frozen dough: II. Effects of freezing and storage conditions on the stability of yeasted doughs. Cereal Chemistry, 56, 424–6.
Hlynka, K. and Van Eschen, E.L. (1965) Studies with an improved loaf-softness tester. Cereal Science Today, 10, 84–7.
Ito, S. and Hodge, D.G. (1985) Some proposed new cream stabilizers. FMBRA Bulletin No. 5, CCFRA, Chipping Campden, UK, pp. 204–9.
Kear, H. (1995) The Milton Keynes Process, in Proceedings of the 79th Conference of the British Society of Baking, November 1995.
Kennedy, C.J. (1998) Formation of ice in frozen foods and its control by physical stimuli, in The Properties of Water in Foods, ISOPOW 6 (ed. D.S. Reid). Blackie Academic & Professional, London, UK, pp. 329–64.
Lorenz, K. and Kulp, K. (1995) Freezing doughs for the production of bread and rolls in the United States, in Frozen and Refrigerated Dough and Batters (eds. K. Kulp, K. Lorenz and J. Brummer). American Association of Cereal Chemists Inc., St Paul, MN, pp. 135–54.
Manley D. (2000) Technology of Biscuits, Crackers and Coolies, 3rd edn. Woodhead Publishing, Cambridge, UK.
Matz, S.A. (1962) Food Texture. Avi Publishing, Westport, CT.
Micka, J. (1939) Study of checking and pH in cracker and biscuit product. Cereal Chemistry, 16, 752–64.
Morris, V.J. (1990) Starch gelation and retrogradation. Trends in Food Science and Technology, 1, 2–6.
Pateras, I. (2007) Bread spoilage and staling, in Technology of Breadmaking (eds.
S.P. Cauvain and L.S. Young). Blackie Academic & Professional, London, UK, pp. 275–98.
Pence, J.W. and Standridge, N.N. (1955) Effect of storage temperature and freez-ing on the firmfreez-ing of a commercial bread. Cereal Chemistry, 32, 519–26.
Rao, P., Nussinovitch, A. and Chinachoti, P. (1992) Effects of surfactants and amylopectin recrystallization and recoverability of bread crumb during stor-age. Cereal Chemistry, 69, 613–18.
Reid, D.S. (1998) Freezing – nucleation in foods and antifreeze actions, in The Properties of Water in Foods, ISOPOW 6 (ed. D.S. Reid). Blackie Academic &
Professional, London, UK, pp. 273–84.
Rittig, F.T. (2005) Lipopan F BG – unlocking the natural strengthening potential in dough, in Using Cereal Science and Technology for the Benefit of Consumers (eds. S.P. Cauvain, S.E. Salmon and L.S. Young). Woodhead Publishing, Cam-bridge, UK, pp. 147–51.
Robb, J. (1985) Pastry technology: cracking of frozen meat pie pastry. FMBRA Report No. 126, CCFRA, Chipping Campden, UK.
Robb, J. (1991) Moisture migration in apple pies. FMBRA Report No. 145, CCFRA, Chipping Campden, UK.
Roos, Y.H. (2007) Water activity and glass transition, in Water Activity in Foods (eds. G.V. Barbosa-Canovas, A.J. Fontana Jr, S.J. Schmidt and T.P. Labuza).
Blackwell Publishing, Oxford, UK, pp. 29–46.
Russell, P. (1985) Shelf-life and staling, in The Master Baker’s Book of Bread-making, 2nd edn (ed. J. Brown). Turret Wheatland, Rickmansworth, UK, pp. 431–40.
Saleem, Q., Wildman, R.D., Huntley, J.M and Whitworth, M.B. (2003) A novel application of speckle interferometry for strain measurements in semi-sweet biscuits. Measurment Science and Technology, 14, 2027–33.
Saleem, Q., Wildman, R.D., Huntley, J.M. and Whitworth, M.B. (2005) Mod-elling biscuit checking using the finite element method, in Using Cereal Sci-ence and Technology for the Benefit of Consumers (eds. S.P. Cauvain, S.E. Salmon and Young, L.S.). Woodhead Publishing, Cambridge, UK, pp. 439–44.
Schoch, T.J. (1945) The fractionation of starch. Advances in Carbohydrate Chem-istry, 1, 247–8.
Schoch, T.J. and French, D. (1947) Studies on bread staling: 1. Role of starch.
Cereal Chemistry, 24, 231–49.
Screen, A.E. (1988) Producing frozen cake batters. FMBRA Bulletin No. 3, CCFRA, Chipping Campden, UK, pp. 126–32.
Wenlock, R.W., Sivell, L.M., King, R.T. (1983) The nutritional composition of British bread – a nationwide study. Journal of Science, Food and Agriculture, 34, 1302–18.
Wiggins, C. and Cauvain, S.P. (2007) Proving, baking and cooling, in Technol-ogy of Breadmaking (eds. S.P. Cauvain and L.S. Young). Blackie Academic &
Professional, London, UK, pp. 120–48.
Wilhoft, E.M.A. (1973) Recent developments on the bread staling problem.
Bakers’ Digest, 47, 14–21.
Williams, T and Pullen, G. (2007) Functional ingredients, in Technology of Bread-making, 2nd edn (eds. S.P. Cauvain and L.S. Young). Springer, New York, pp. 51–92.