Other bakery ingredients

5.1 Is it true that yeast requires oxygen before it can work correctly?

As long ago as 1875, Louis Pasteur showed that fermentation could take place in the complete absence of oxygen. He also showed that the presence of oxygen inhibited fermentation but increased yeast growth and respiration. Pasteur's observation that 'fermentation is life without air' is a well-known quotation in food science.

If oxygen is introduced in increasing quantities into a fermenting sugar solution, fermentation slows down and respiration takes over. The process can be described chemically as follows:

C6H12O6 + 6O2 ^ 6H2O + 6CO2

Glucose + oxygen water + carbon dioxide

In practice the theoretical respiration equation is never realised because much of the carbon dioxide that is liberated combines with other materials to form yeast cell substance. The yeast manufacturer makes use of the effect of oxygen by blowing large volumes of air through the fermenter to discourage fermentation and so maximise the yield of yeast.

Some confusion about the relationship between yeast and oxygen may arise because of the well-known effect of yeast scavenging oxygen molecules from a bread dough during mixing (Chamberlain, 1979). The importance of this observation is that it explains why the effect of ascorbic acid as an oxidising agent is limited to the mixer in breadmaking (see 6.9).

64 Baking problems solved Reference

CHAMBERLAIN, N. (1979) Gases - the neglected ingredient, in Proceedings of the 49th Conference of the British Society of Baking, British Society of Baking, pp. 12-17.

5.2 How does bakers' yeast produce carbon dioxide in breadmaking?

Yeast produces carbon dioxide gas in breadmaking by fermenting the sugars that are present in the ingredients or the formulation. The basic reaction is represented in the following manner:

C6H12O6 ^ 2C2H5OH + 2CO2

Glucose ethyl alcohol + carbon dioxide

You will notice a significant difference in the reaction compared with that given in the previous question. In particular fermentation yields the production of ethyl alcohol whereas respiration does not. The fermentation process does not require the presence of oxygen.

The yeast cell contains large numbers of enzymes which are required for the fermentation and respiration. These enzymes are held within the cell, provided the cell wall remains intact. About 14 different enzymes are involved in the fermentation process.

When a dough is made the yeast first feeds on the naturally occurring sugars in the flour (glucose and sucrose). As these are used up the enzyme complex begins to provide more sugars by breaking down other flour components. The damaged starch is important in this context because of its conversion ultimately to maltose. This is why we are concerned with the enzymic activity and damaged starch levels in the flour that we use (see 2.5 and 2.6). If we cannot provide a substrate (food) for the yeast it will stop working and carbon dioxide production will cease. When the CBP was introduced in the 1960s the type of bakers' yeast then used was unable to provide carbon dioxide gas in the critical early stages of baking and it became necessary for the yeast strain to be changed (Williams and Pullen, 1998). Though the precise nature of the changes is not public knowledge it undoubtedly was related to the enzyme activity within the yeast cell.

In modern no-time breadmaking processes we are concerned only with the production of carbon dioxide by the yeast. Respiration and growth are not required. Indeed the conditions within a bread dough formulation and the timescales concerned are unlikely to be suitable for either process to take place to any significant degree.


WILLIAMS, A. and PULLEN, G. (1998) Functional ingredients in Technology of Breadmaking (eds S.P. Cauvain and L.S. Young) Blackie Academic & Professional, London, UK, pp. 45-80.

5.3 We have been advised to store our compressed yeast in the refrigerator but our dough temperature is much higher: is this the correct thing to do?

The advice that you have been given is absolutely correct. Once compressed yeast has been prepared it should be kept under refrigerated conditions (4 °C) until it is required for doughmaking. Storing yeast at higher than refrigerated temperatures results in the progressive loss of its gas production potential. Williams and Pullen (1998) showed how dough proving times were increased when compressed yeast was stored at 10 and 15 °C. By the time that the yeast had been held for 14 days at 15 °C the proving time required for the dough had doubled (see Fig. 13). Storing compressed yeast at dough temperatures would be a disaster!

It is therefore very important that the yeast is stored under the best possible conditions. Storing at 4 °C reduces the potential for unwanted activity within the block (see 5.4). The compressed yeast is usually transported under refrigerated conditions and on delivery should be moved as quickly as possible to storage at a similar storage temperature. The blocks should be left in the refrigerator as late as possible before use. Once dispersed into the dough the cells soon warm and produce carbon dioxide.

Variations in gassing activity will show as variations in proving volume for a given time. If you are not able to adjust the proving time to compensate for this variation (few bakeries can) then you will get variations in bread volume and problems with product shape, e.g. ragged breaks from under-proving.

7 days 14 days

Yeast storage temperature

Fig. 13 Effect of storage temperature on yeast activity.


WILLIAMS, A. and PULLEN, G. (1998) Functional ingredients in Technology of Breadmaking (eds S.P. Cauvain and L.S. Young) Blackie Academic & Professional, London, UK, pp. 45-80.

5.4 What are the causes of the dark brown patches we sometimes see on compressed bakers' yeast? Do they have any effect on baked product quality?

The brown patches are autolysis and comprise dead yeast cells. They usually come from having kept the yeast too long or at too high a storage temperature (see 5.3). There is no food available for the yeast cells in the compressed block. Storage at around 4 °C limits the activity of the cells but if the temperature rises sufficiently then oxidation processes begin and the cells break down. This means that there will be a loss of gassing activity when the yeast comes to be used in the dough.

In addition to the loss of gassing potential the contents of the affected cells may leak out of the ruptured membranes. The yeast cells contain a suite of enzymes and other chemicals. The release of proteolytic enzymes and glutathione (a reducing agent) are bad news for breadmaking because both materials will attack the gluten structure of the dough and weaken it. Subsequently the affected doughs will exhibit a lack of gas retention, i.e. a loss of volume and a more open cell structure. In more severe cases the doughs may become sticky and difficult to process.

We suggest that wherever possible you do not use the affected yeast and that you check the settings and efficiency of your refrigerator.

5.5 We have recently been experiencing 'weeping' from our non-dairy cream formulation. This shows itself as a 'soggy' layer where the cream is in contact with the cake. How can the problem be cured?

In order to solve this problem we first have to decide its origins. There are three possibilities: fat or moisture migration, or both.

Fat migration can occur when the oil fraction of the cream filling is too large because it does not remain trapped within the cream structure and sinks into the cake layer below under the influence of gravity. In order to decide the oil to solid fat ratio you will have to consider a number of factors including:

• the product storage temperature - the higher the storage temperature, the higher the SFI needs to be;

• the eating qualities of the cream - the softer the eating character, the greater the liquid oil fraction will have to be.

Fat migration is not influenced by storage humidity. To reduce fat separation you may find some advantage in adding a suitable emulsifier to the cream formulation, e.g. lecithin or glycerol monostearate, or a stabiliser such as gelatine.

Moisture migration occurs when the water activity of the cream is not in equilibrium with that of the cake. The causes and cures for moisture migration have been reviewed by Cauvain and Young (2000). Your problem is associated with moisture migration by diffusion: where two materials are in direct contact with unequal water activities the moisture moves from the wetter to the drier component. The main solution to the problem of moisture migration is to balance the component water activities and reduce the driving force for change. This will require a reformulation of cream or cake, or both. You should have the component water activities measured and reformulate to reduce any differential. Adjusting salt or sugar levels can be advantageous, or additions of glycerol may be used. Placing a moisture-proof barrier between the two components is possible but difficult given the porous nature of cakes.

Moisture migration is also strongly influenced by the storage temperature, with migration being reduced as the temperature is lowered. Unlike fat migration, moisture migration is affected by storage humidity with migration moving at a faster rate when there is a greater difference between the component and storage humidities.


CAUVAIN, S.P. and YOUNG, L.S. (2000) Bakery Food Manufacture & Quality: Water control and effects, Blackwell Science, Oxford, UK.

5.6 The chocolate fondant on our cream eclairs falls off the top of the casing and gathers on the tray underneath as a sticky syrup. What causes this and how can we prevent it?

The chocolate fondant contains undissolved sugar particles which tend to make it hygroscopic, that is likely to absorb water. As more water is taken up by the fondant then the fondant becomes more liquid and likely to flow. If you are putting the fondant on to the curved top of the eclair shell then it can readily flow down the sides.

The water that causes this problem will derive from the other components of the eclair. Usually the source will be the cream which has a very high water activity (equilibrium relative humidity, ERH) and the moisture readily diffuses through the porous and dry choux shell. The moisture that gathers at the shellfondant interface acts like a lubricant and helps the fondant flow.

This is not an easy problem to eliminate because of the diverse nature of the three components in the composite product. Some points to consider are as follows:

• The fondant will always contain undissolved sugar and therefore have hygroscopic properties. However, these may be reduced to some extent by replacing some of the sucrose with a glucose syrup, adjusting the water as necessary.

• Adding a small quantity of fat to the fondant, say 5-6%.

• Lowering the ERH of the cream in order to reduce the driving force for moisture migration. The options may be limited though sucrose or even glycerol additions may help.

• A change to a slightly more permeable packing may help by allowing some loss of moisture to the external atmosphere, but beware that this may lead to the whole product drying out too quickly.

• Try icing the base of the eclair shell because this is usually flat.

• Look carefully at the tray in which you stand the eclairs. If the eclair does not stand level in the tray then there is always a potential for the fondant to flow.

5.7 When we changed our supply of bun spice in our hot cross buns we experienced problems with slow gassing in the prover and flowing of the buns during baking. What can we do to avoid these problems?

Many spices have an adverse effect on yeast and will inhibit gas production. The higher the concentration of the spice, the greater will be the effect. It appears that the change from one spice supply to another has resulted in the inadvertent addition of a more concentrated form to the dough, which is the equivalent of a higher spice level even though the weight of added spice has remained constant. Alternatively the new spice formulation you are using may have a concentration of one or more spices which have a significant effect on gas production.

The problem you describe can occur whether you are using a liquid or dry spice. Try to make sure that the yeast and the spice are kept separate for as long as possible in the mixing process. In the case of a liquid spice and some mixing operations you may be able to hold the liquid spice until after the yeast has been fully dispersed.

The flowing that you see almost certainly comes about because of the same problem. Direct contact between the spice and the yeast may have caused disruption of the yeast cells with subsequent leakage of the proteolytic enzymes and glutathione which both weaken the gluten network in the dough. If sulphur dioxide or sodium metabisulphite have been used as preservatives in the spice, residues of these chemicals can act as reducing agents and weaken dough structures.

If the problem persists after you have taken suitable precautions during mixing or after adjusting the levels of addition you might try using less spice in the dough and more in the glaze for the products to maintain product flavour.

5.8 We are making a fruited bun product and from time to time experience problems with the product flowing out during proving and baking. What is the cause and how can it be remedied?

There are a number of possible reasons for your product flowing during proving and baking. They include the following:

• Too much water in the dough. This may come from incorrect levels of addition or from the fruit if you have been soaking it.

• The presence of the reducing agent glutathione arising from the disruption of yeast cells that have not been stored correctly (see 5.3).

• Too much humidity in the prover which causes solubilisation of the proteins in the dough.

• Residual sulphur dioxide in the dried fruit.

Since the problem is associated with a fruited product we suggest that you thoroughly wash and dry the fruit before using it. If the problem persists then you should look for a processing cause, such as excess humidity in the prover.

5.9 We wish to use milk powder in our fermented goods and have heard that it is advisable to use a heat-treated form. Why is this?

The use of fully heat-treated milk or milk powder products is essential if you are to avoid losses in product volume. In the case of liquid milk typical heat-treatment conditions would require raising the temperature to around 80 °C and holding it at that temperature for some 30 minutes before cooling and use. If dried milk powders are to be used it is important that they have been subjected to a similar temperature to that given above (Collins et al, 1970).

Similar problems with loss of volume can occur if inadequately treated milk powder is used in the production of sponge goods. On some occasions a collapse of the cake structure and the formation of a 'core' (an area of coarse, dark coloured cell structure) may occur.

The adverse effects of inadequately treated milk arise because the globulin proteins normally present have not been denatured. The normal pasteurisation process applied to milk does not denature the globulins which can interfere with the stability of the gas bubbles in the proving dough or baking cake.

The suitability of a milk powder for baking can be assessed with a small-scale baking test or by employing the Swortfiguer cloud test (Swortfiguer, 1958). A clear or slightly cloudy solution at the end of the test indicates that the milk powder has been adequately treated.


COLLINS, T.H., OVERTON, M.J. and REDMAN, B.I. (1970) The use of milk in breadmaking. FMBRA Report No. 40, CCFRA, Chipping Campden, UK. SWORTFIGUER, M.J. (1958) Is there a simple method by which we may determine whether a sample of non fat dry milk has received proper treatment?, Baker's Digest, October, 78.

5.10 Does the addition of mould inhibitors have any significant effects on baked product quality?

The most obvious effect of mould inhibitors will be on the smell and flavour of the product. This may be particularly noticeable if the product is heated, as in the case of preparing toast from bread slices with an inhibitor in the formulation.

Even if there is no effect on flavour we can expect there to be some effect on yeast activity in fermented products. Yeasts are a class of microorganism and so will be affected in a similar manner to moulds, namely that their activity is inhibited. In the case of bakers' yeast the lower activity will show as slower gas production in the dough which may lead to under-proving and lack of oven spring in the resultant bread. Any such loss of activity is usually overcome by raising the added yeast level in compensation. In cake and other confectionery products the presence of mould inhibitors has no effect on gas production from the baking powder reaction.

It is worth noting that while not a direct effect on baked product quality, the mould-free shelf-life of the product is extended through the use of mould inhibitors. The effect of some mould inhibitors is enhanced when the pH of the product is lowered so that the increase in mould-free shelf-life becomes more dramatic. This is certainly the case with the mould inhibitor potassium sorbate when used in the manufacture of cakes (Cauvain and Young, 2000)


CAUVAIN, S.P. and YOUNG, L.S. (2000) Bakery Food Manufacture and Quality: Water control and effects, Blackwell Science, Oxford, UK.

5.11 What are the functions of salt in baking?

Common salt, more correctly sodium chloride, provides a number of functions in baked products:

• It contributes to product flavour, e.g. in bread.

• It lowers product water activity and therefore extends product shelf-life (Cauvain and Young, 2000).

• It inhibits yeast activity and so can be used to control fermentation in bread-making (Williams and Pullen, 1998).

• It modifies dough rheology in breadmaking, making the dough less sticky.

• It contributes to the formation of bread crust colour, especially in longer fermentation systems.

Salt levels will vary in baked products according to the functional needs. In general, salt levels have fallen gradually in foods because of concerns over high levels of sodium in many diets.

Although potassium chloride will have similar functional effects in baking, if used to replace sodium chloride on an equal weight basis it confers a largely unacceptable bitter taste to the final product.


CAUVAIN, S.P. and YOUNG, L.S. (2000) Bakery Food Manufacture and Quality:

Water control and effects, Blackwell Science, Oxford, UK. WILLIAMS, A. and PULLEN, G. (1998) Functional ingredients in Technology of Breadmaking (eds S.P. Cauvain and L.S. Young) Blackie Academic & Professional, London, UK, pp. 45-80.

5.12 What are the correct proportions of acid and alkali to use in baking powders?

The principal alkali used in baking powders is sodium bicarbonate and it is this ingredient that supplies the carbon dioxide gas which inflates powder-raised goods such as cakes and sponges.

In order for the gas to be evolved at the most suitable time during baking a food acid is added to the formulation. Sodium bicarbonate will release carbon dioxide by thermal decomposition at 90 °C but this is far too late to be of use because at that temperature the structure of the product is effectively set and unable to expand any further. A number of suitable acids are available, each having a different rate of reaction with the sodium bicarbonate and each leaving a different residual salt in the baked product. Both properties are important, the first because it affects the overall expansion of the product and the latter because it affects the flavour.

The correct proportion of acid to sodium bicarbonate varies according to the chemistry of the acid. The correct proportion of acid to sodium bicarbonate is normally considered to be that which takes the reaction to completion and is referred to as the neutralising value. For commonly used acids the appropriate proportions for 1 part of sodium bicarbonate are:

• mono (acid) calcium phosphate (MCP, ACP) - 1.25;

• cream powder (SAPP on a neutral powder base) - 2.0;

• cream of tartar (potassium hydrogen tartrate) - 2.2;

Some baking acids are available in different grades which control their rate of reaction with sodium bicarbonate.

5.13 Why is sodium bicarbonate frequently used alone or in excess to the normal baking powder for the production of ginger products?

The idea of using an excess of sodium bicarbonate in ginger products is no doubt based on traditional practices and any explanation would be speculative. Despite its traditional basis the practice does have a practical advantage. Under the influence of moisture and heat, carbon dioxide is liberated from any sodium bicarbonate left after the normal acid-base reaction and sodium carbonate remains as a residue. The carbonate is alkaline and will react with sugars, particularly invert sugar to form complex carbon compounds that are brown in colour. In this way the excess of sodium bicarbonate aids the formation of the dark brown colour that characterises ginger products.

If you look closely at the cut surface of baked ginger cakes you may see that the colour is more intense toward the base and sides of the cross-section. These are the areas that are baked first and so have been held for a longer time at the oven temperature and the browning reaction has proceeded further than the more moist centre areas of the cake.

The residual sodium carbonate has a characteristic 'washing soda' taste which is why we normally seek to neutralise the sodium bicarbonate in most baked products. However, the strong flavour of ginger will commonly mask the carbonate after-taste.

Continue reading here: We are using walnuts in our gateau buttercream filling and find that it turns black It does not appear to be mould What is the cause of this discoloration

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