What are the critical properties of fats for making bread cakes and pastries
To answer this question it is first necessary to be clear about the definition of a fat. In the bakery this is usually the term given to a material that is a blend of liquid oils and solid fats from different sources, usually vegetable in origin. Podmore (1997) provides a comprehensive review of the nature and structure of fats. The basic building blocks of fats are the fatty acids, of which there are three. The fatty acids of the triglyceride may be the same as one another or different. All natural oils and fats are mixtures of glycerides and the properties of the individual fats and oils depend on the quantity and distribution of the different glycerides that may be present.
Since fat properties are related to the glycerides present a detailed knowledge of the composition of a compound fat can be useful. This is commonly obtained using gas chromatography (GC) or high-performance liquid chromatography (HPLC). However, such analytical techniques require expensive and specialised equipment that is not within the scope of many laboratories. The fatty acid composition is related to other more readily measurable properties of fats and oils.
A readily known measurement is the iodine value which measures the proportion of double carbon bonds in the fat and indicates the degree of saturation present. In some fatty acids adjacent carbon atoms in the chain may be joined by a double bond so that fewer hydrogen atoms are attached than theoretically possible and so they are called 'unsaturated'. In 'saturated' fats two bonds form between two carbon atoms in the chain while the two remaining bonds are formed with two individual hydrogen atoms.
Temperature (°C) Fig. 7 Examples of fat solid fat index profiles.
Traditionally the 'slip' or 'melting point' of a fat was used to characterise its performance in baking. However, since many commercial fats are compound mixtures of triglycerides the melting point is often spread over a wide range of temperatures and so has limited value. It is now more common to refer to the Solid Fat Index (SFI) of a fat which considers the proportion of a compound fat which is solid at a given temperature.
Fat SFIs are commonly measured using nuclear magnetic resonance (NMR) and sometimes NMR values for fat are quoted rather than the SFI. Whichever nomenclature is used the temperature at which the measurement is made should be quoted, e.g. NMR20 indicates the percentage of solid fat present at 20 °C (see Fig. 7).
In the past measures of fat firmness using cone penetrometry have been used to indicate the characteristics of given fats, e.g. 'C' values (Haighton, 1959). The firmness of a fat at a given temperature is strongly influenced by the proportion of oil to solid; however, this is not the only relevant property of fat to be considered. Solid fats may exist in different crystalline forms depending on their temperature history in production and use. The size of the fat crystals also affects their functionality. Small crystals have a larger surface area relative to large ones and so are more able to retain large quantities of liquid oil within the crystal matrix. The crystalline form of a fat is not usually assessed or measured even though it may affect the fat performance.
40 Baking problems solved References
HAIGHTON, A.J. (1959) The measurement of the hardness of margarines and fats with cone penetrometers. Journal of the American Oil Chemical Society, 36, 345-348.
PODMORE, J. (1997) Baking fats, in The Technology of Cake Making (ed. A.J. Bent), Blackie Academic & Professional, London, UK, pp. 25-47.
3.2 Our bread doughs prove satisfactorily but they do not rise in the oven. On some occasions they may even collapse and blisters may form on the dough surface in the corners of the pans. What is the cause of these problems?
A lack of oven spring or collapse of the dough in the oven usually signifies a lack of gas retention in the dough. This may arise for a number of different reasons but your comment on the formation of blister on the dough surface in the corner of the pans strongly suggests that your problem comes from a lack of fat or other suitable lipid (e.g. emulsifier) in your improver or bread formulation. The problem can be too low a level or an inappropriate character of the ingredient.
In modern, no-time breadmaking systems, e.g. the Chorleywood Breadmak-ing Process (CBP), the addition of a fat or emulsifier is important in ensuring adequate gas retention in the dough (Cauvain, 1998). It has been known for quite some time that it is only the solid portion of the fat that can affect dough gas retention and in no-time doughmaking processes it is important that a proportion of any added fat should remain as solid in the dough at the end of final proving. Since typically final proving is carried out at around 40-45 °C, the fat melting point must be above 45 °C.
The necessary level of solid fat to achieve the required effect at 45 °C can be quite small and values as low as 0.02% flour weight have been quoted. However, it is known that the minimum level of fat required varies with flours. In general higher levels of fat appear to be required with stronger white flours and a general recommendation of 0.7% of a compound bakery shortening was the original blanket recommendation in the CBP because this ensured that a sufficiently high level of solid fat remained in the dough at the end of proving.
Improved gas retention with wholemeal and brown flours requires considerably higher levels of added fat than white flours. Cauvain (1998) provides an example for wholemeal bread made by the CBP where maximum bread volume was obtained when added fat levels reached 4% of the flour weight. It is also known that the loss of gas retention which comes from prolonged storage of flour can be compensated with the addition of high levels of a suitable fat.
It is most likely that the fat confers improved gas retention in bread dough by helping to control gas bubble size and stability. Composite bakery shortenings are a mixture of oil and solid fat at dough temperatures but it is only the solid fat portion that can play the necessary gas bubble stabilising role. The molecules of the solid fat portion align themselves at the interface of the gas bubble and the liquid dough phase and play a part in determining the size of the gas bubbles as well as their stability. As the temperature rises in the dough some of the fat molecules melt and lose their ability to stabilise the gas bubbles. Eventually all the fat melts and other materials, principally the gluten, are left to maintain gas bubble stability. A key role for fat may be the prevention of coalescence of gas bubbles in the dough in the early stages of baking.
Emulsifiers are commonly used to replace fat in bread doughs on the basis that they can be used at lower levels. In simplistic terms they may be considered as specialised fats with a high melting point. They play a similar role to fats in stabilising gas bubbles in the dough. However, their melting profile is quite different from that of fats in that they remain solid to much higher temperatures in the dough, typically around 60 °C.
The blisters observed on the dough are gas bubbles that have become excessively expanded but are unstable. When the dough reaches the oven the gluten network is unable to cope with the gas bubble expansion and individual bubbles become over-expanded, perforate and collapse. Collectively they lead to total dough collapse. The addition of a suitable level of a high melting point fat should overcome this problem.
Continue reading here: What is the role of fat in the manufacture of puff pastry
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