1.4. Other ingredients - salt, sugar and emulsifiers
Salt's main function is to bring out the flavour of the baked product. Salt tends to bring out the good flavours and mask the off-flavours. Usage levels are normally between 1,8 % and 2,2 %. Legislation may vary from country to country because the intake of too much salt is considered as a health risk. In Belgium for instance the maximum allowed is 1,8 %, while in France 2,0 % is allowed. In Scandinavia one has to pay extra taxes if the salt level in the bread is higher then 1,2 %. Bread made with less then 1,6 % salt will taste insipid and bread made with more then 2,2 % will taste too salty.
In addition to impacting flavour, salt also inhibits fermentation due to the osmotic pressure effect. Yeast cells will partially dehydrate due to the osmotic pressure. This can be illustrated easily by putting some salt on fresh yeast. After a while the yeast will liquefy due to the fact that the salt will attract the water from the yeast cell. As the cell membrane is semi permeable, water will migrate from the cell and the mixture will seem to liquefy. In reality the yeast cell undergoes a change which can be compared with the change that happens to a grape when it becomes a raisin, it just dries out.
The fact that salt influences the fermentation can be used to control the fermentation : salt can be added for instance to sponges to slow down the fermentation rate. Slowing down fermentation rate means that less sugars are metabolised into acids. The result is that the pH of the dough will be higher and the crust colour will be darker. To remember that high pH gives a darker colour, one can think about a chocolate cake. Chocolate is alkaline and to get a darker, deeper colour of a chocolate cake, one must increase the pH.
Salt toughens the gluten. Weaker flours could actually be strengthened by adding salt. Salt lengthens the mixing time so it is common to delay the addition of the salt to the mixer. Faster flour hydration is also seen with delayed salt. The reason why salt toughens the gluten must be sought in the fact that gluten is made of negatively charged proteins. Negatively charged molecules will repel and not attract each other. It is believed that the positive sodium-ions Na+ of the salt play a role in bringing the protein molecules closer to each other.
Lastly, bread with no salt will also has a crust which is lighter in colour (given the same baking time and oven temperature). This can be explained as follows. Salt will slow down fermentation, so when there is no salt, the yeast activity will increase i.e. the yeast will metabolise more sugar in a given period of time. As a result there will be less sugars left in the dough and the pH of the dough will be lower (more acids will be formed). Sugars play (together with proteins, moisture and heat) an important role in the Maillard reaction. But the Maillard reaction is also influenced by the pH : a higher pH will speed up the Maillard reaction. So in this case where the pH is lower and where there are less sugars left, the colour of the crust is lighter.
Recently there has been quite some pressure on the bakery sector to reduce the salt content in bread, cakes, muffins etc. Potassium chloride as an acceptable substitute for sodium chloride as it as basically the same rheological effects on the dough. If however the salt is replaced by the same amount of potassium chloride the bread will have a bitter after taste. This after taste greatly disappears after 2 or 3 days. It also can be masked by the use of eggs and butter. So the problem does not occur in products such as muffins or cakes.
Potassium chloride also has a lower inhibiting effect on the yeast. So proofing times will be shorter. The same thing is true for the mixing times. When using a 2 % NaCl level on the flour, and the salt is replaced by a 50:50 mixture of sodium chloride and potassium chloride, the mixing time will be about 15 % shorter. So if you have a mixing time of 20 minutes it will become 17 minutes about.
Finally it needs to be noted that potassium chloride dissolves not as easy in water compared to sodium chloride. Hence it is important to choose "fine" potassium chloride and not a coarse grade. The undissolved grains will cause dark brown spots on the crust of the product. These are quite visible on products like muffins and cakes.
Sugar's main function is to provide food for the yeast. In normal bread production, 3,0 to 3,5 % fermentable solids are required to sustain yeast activity. This food supply can come from added sugar or from the enzymatic conversion of the starch to sugar or from a combination of both. Therefore sugar is not an essential ingredient.
Starch indeed belongs chemically to the group of carbohydrates : it is a long chain of glucose units and according to its structure there are two kinds :
Glucose, fructose and galactose are monosaccharides; sucrose, lactose and maltose are disaccharides. Dextrins also contain a large number of glucose units but not as much as starch.
Secondary functions of sugar are related to sugar that is not metabolised by the yeast and which is called residual sugar. As residual sugar levels are higher, crust colour is darker, taste is sweeter, and moisture retention is improved due to the hygroscopic properties of sugar.
There are many kinds of sugar used in the industry. The most common is 42 HFCS (42 high fructose corn syrup). The 42 means that 42 % of the 71 % solids found in the corn syrup is fructose. Higher numbers mean that the fructose content of the syrup is higher and hence the syrup will taste sweeter.
Different sugars also give a different sensation of sweetness. Take for instance glucose and fructose which chemically have exactly the same formula (C6H12O6) but the molecule has a different structure :
It is commonly known that fructose is about twice as sweet as glucose. The following table gives an overview of the relative sweetness of different sugars :
Lactose and maltose have the following molecular structure.
The main difference is however that lactose is a non-fermentable sugar : it will not be metabolised by the yeast and remain in the dough. In view of it's rather low sweetness, it will not give a sweeter product but it will influence the crust colour (Maillard reaction) and because of its hygroscopic nature delay staling.
Sugar has the same effect as salt : if too much is used, yeast activity will slow down. This effect can be seen from a 5 – 6 % sugar level. In order to compensate one can add more yeast. The sugar/yeast ratio should be 3/1. If you want to make a product that contains 15 % of sugar, the yeast level should be 5 % (baker's percentage).
Finally one should remember there are also "natural" sugars such as honey and fruit juices.
Fats are used in bread production to provide overall lubrication. It becomes necessary to use a small amount to facilitate slicing : 0,7 – 1,0 % will suffice to facilitate slicing.
Addition of fat helps in the handling of the dough during the make-up process. Besides lubricating the baked crumb, fat also lubricates the dough and this eases dough expansion in the proofer and in the oven. It will also tenderise the crust and improve shelf life by retarding staling.
Fats are constantly in the media with regards to health risks. Presently we have the hype around trans fatty acids. Without going into too much detail, one can divide the fats into a number of categories :
Finally cholesterol is only present in animal fats.
They primarily function as nutritional supplements. Milk is high in lysine (an essential amino acid) and calcium and the overall nutritional quality of the milk protein is excellent. European bakers prefer the use of liquid milk above the use of powder milk. Liquid milk may be less user friendly (storage, perishable), however it has the advantage that no dry matter remains in the product. Indeed, milk powder (or rather the denaturated proteins present in the milk powder) will not dissolve completely in the water and remain as dry solids in the crumb. This will give a dryer, less moist crumb. However it should be kept in mind that the milk must have been heat treated because the serum protein in milk has a weakening effect upon the gluten protein in wheat flour.
Besides improving nutritional quality, milk improves the flavour if used in a high enough amount, the dough handling and overall processing tolerance :
Vital wheat gluten
Vital wheat gluten is the natural wheat protein extracted from flour which still retains all of its gluten forming characteristics. It is added to the dough to help strengthen a weak flour or to obtain additional loaf volume. A 1 % addition of wheat gluten will increase the flour protein content by 0,6 % and increase the absorption by 1,5 %. By adding wheat gluten to the recipe, mixing and fermentation times are generally increased and tolerances improve. They mainly are used in systems where the gluten network is weak or where it has to carry extra ingredients such as raisins, different types of grains, extra fibres etc.
Malting is a process applied to cereal grains, in which the grains are made to germinate by soaking in water and are then quickly halted from germinating further by drying/heating with hot air. Thus, malting is a combination of two processes: the sprouting process and the kiln-drying process. Kilns are thermally insulated chambers, or ovens, in which controlled temperature regimes are produced. They are used to harden, burn or dry materials. In the bakery it is not unusual to add malted wheat, malted wheat flour, malted barley flour or any combination of these to wheat flour.
The malt used in the bakery is prepared from a cereal grain, usually barley, by moistening the grain with water, allowing it to germinate (sprout) under controlled conditions, drying it with warm circulating air and removing the sprout. The natural processes accompanying sprouting create or release in active form large quantities of enzymes such as a- and ß-amylases. Malt flour is the ground modified grain.
Diastatic malt flour contains these active enzymes whereas in non-diastatic malt the enzymes have been deactivated. The non-diastatic malt flour is used mainly to supply flavour and colour to baked products. The reasons for the use of malt supplementation are principally:
The amylolytic enzymes of importance to bakers are a-amylase (or dextrinising amylase) and ß-amylase (saccharifying enzyme). a-Amylase splits the starch molecules at random, producing dextrins of various molecular sizes and also reduces the viscosity of the susceptible starch suspensions. ß-Amylase acts on the end of the starch molecule, resulting in the progressive release of maltose. However this enzyme cannot attack the starch molecule inside the points at which it is branched.
When the two enzymes work in conjunction, a much greater conversion of starch into fermentable sugars (mainly maltose and glucose) results than when either of them acts alone. This combined action is typical of malt containing both amylolytic enzymes. Diastatic malt syrup is also used in some formulations. Malt syrups are concentrated water extracts of the malted grain. There are also blends of malt syrup with corn syrup and they are being sold in both liquid and dried forms.
Malt is fairly high in vitamins and essential amino acids and from this point of view it is a nutritionally valuable additive. Vitamins occurring in malt are biotin, niacin, pyridoxine, riboflavin, thiamine and choline (belongs to the vitamin B group).
Both diastatic and non-diastatic malt contain considerable quantities of sugars, including glucose and maltose. The first one is rapidly consumed by the yeast during fermentation, the second one is fermented by yeast late in the bread making process when glucose and fructose have been used up.
There are two ways of getting maltose into the dough. One method is to add the sugar to the dough in the form of malt (or high maltose corn syrup) and the other is to rely on the production of maltose from the flour starch by diastatic enzymes. In recent years, the enzymatic action of diastatic malt syrup has been mostly replaced by standardised enzymes isolated from bacterial or fungal cultures.
Diastatic malt products differ from their non-diastatic counterparts in possessing considerable enzymatic activity. The malted grain from which these products are derived is like a hypermarket for enzymes, most of which have never been adequately investigated. The two types which are of importance to the baker are proteolytic enzymes and amylolytic enzymes.
The action of a-amylase and ß-amylase have been described (see above or scroll down to read the part on enzymes).
The action of ß-amylase on undamaged starch and ungelatinised starch granules is very slow. a-Amylase does attack granules with no visible damage at an appreciable rate. Both enzymes attack gelatinised starch very rapidly but this reaction cannot be of much importance in the bread making process because the starch in dough does not become gelatinised until virtually all of the enzyme activity has been destroyed by heat. Starch granules which have been mechanically damaged during milling are also broken down by both enzymes. Perhaps 3 or 4 % of the starch granules is visibly damaged. This mechanical damage is due to shearing forces and pressures encountered during the milling process. Consequently the proportion of damaged granules is a function of the milling conditions and may vary not only from mill to mill but also between flours of different extraction rates. However flours of similar extraction made from the same types of wheat (hardness of the wheat kernel) and ground at the same mill should contain a rather constant proportion of damaged starch.
The capacity of malt to convert starch into reducing sugars is expressed as the Linter value (°L) or as maltose equivalent. When using the standard AACC method degrees Linter equal about 1/4th of the maltose value. In each system, the rating of non-diastatic malt is theoretically zero although in practice malts of 10°L or less are classified as non-diastatic malt. A good barley malt flour might rate as high as 125°L. Commercially available diastatic malt syrups usually have ratings of 20, 40 or 60°L and are described as low, medium or high diastatic malts respectively.
A malt has a diastatic power of 100°L if 0,1 ml of a clear 5 % infusion of the malt, acting on 100 ml of a 2% starch solution at 20°C for one hour, produces sufficient reducing sugars to reduce completely 5 ml of Fehling's solution.
Sometimes diastatic activity is also expressed in Windisch-Kolbach units. These are approximately related to the Linter degrees by the following formula:
°WK = (3,5 x °L) - 16
Diastatic malt syrups are used at a dosage level of 2,0 to 2,5 % on the flour. Larger amounts may darken the crumb, cause excessive fermentation and make the dough too sticky to process efficiently.
The amylolytic enzyme activity of malt products can be reduced by heat treatment. If the heating process is carried far enough to denature nearly all of the enzyme, the product is called "non-diastatic" even though traces of starch hydrolysing activity can be detected. Such malts are used principally to supply flavour and colour to baked products. They also have some effect on texture and supply fermentable carbohydrates and other nutrients to the yeast.
Non-diastatic malt syrups tend to be darker in colour and stronger in flavour then their diastatic counterparts. These differences are due to the more extreme heat treatment which has been applied to the non-diastatic malt during processing, especially during the condensing step.
It is necessary to minimise heat treatment if substantial enzymatic activity is to be retained, while the non-diastatic products cam be evaporated at high temperatures since amylase activity is not desired. Both colour and flavour are intensified by heat mainly through Maillard reactions. Although the flavour of a highly heat treated syrup tends to be strong, it is also inclined to be more bitter and less aromatic than that of a lighter syrup. Malt syrups will also change colour during storage, becoming darker and losing some of the reddish hue which adds attractiveness to the golden brown colour of the bread crust. Also some vitamin and protein content is lost due to the heat treatment.
The colour changes accompanying the caramelisation which result from the high temperatures processing used in the manufacture of non-diastatic malt make the product valuable as a colouring agent. Dark rye breads often contain large amounts of non-diastatic malt syrup although caramel colour can replace malt as colouring agent. On the other hand the use of high roasted malts in white bread is definitely limited by the darkening which is observed even at moderate dosage levels.
Bread improvers (or dough conditioners as they are called in the United States) are additives which are used in small quantities in order to improve the quality of the bread. Some of them are baking aids i.e. it is not possible to find them back in the final loaf, so they don't have to be declared.
In earlier times, baking was a profession where appropriate time could be allocated to mixing, fermentation, proofing and the baking of bread. Adjustments could be made, as needed, for changes in flour, yeast activity, temperature, humidity, and any other environmental conditions that might occur. Today, the bread making operation is largely mechanized, and we desire to produce the same loaf of bread, roll or pizza crust every hour of every day, year after year. The use of dough conditioners has enabled the baker to overcome these challenges and produce uniform, high quality baked goods.
Dough conditioners are used:
Important dough characteristics influenced by dough conditioners include:
They can be divided into 3 main categories : enzymes, oxidising agents, reducing agents. In fact there is a 4th category : emulsifiers which will be described in a separate paragraph.
1) EnzymesPlease read separate chaper on enzymes by going to the following page
2) Oxidising agents
Oxidising agents are used by the baker to improve dough strength. Due to the oxidising action SH-groups in the gluten network will be transformed into –S-S- bonds between the protein chains rendering a stronger gluten network. They will improve dough handling for better machining and contribute to improved gas retention, giving better volume and a more regular grain of the crumb. Some oxidants are fast acting, working in the mixer and early make-up stage. Bromates, which are cancerogenous and which are only allowed in the USA (all other countries in the world put a ban on the usage of bromates), act in the proofer and early oven stage.
One oxidant with which good results were obtained in the United Kingdom is pure oxygen added during mixing. However, since O2 is not on the list of allowed additives, its usage was banned.
Calcium peroxide is an oxidant but is used for its dough drying capabilities. It tends to take away the stickiness without stiffening the dough. It reacts immediately on contact with water.
The most widely used oxidising agent is ascorbic acid or vitamin C. No need to say it is safe to use. However one needs oxygen to be present because ascorbic acid as such is a reducing agent. In the presence of oxygen however it will become dehydroxyascorbic acid and it is actually the dehydroxyascorbic acid reacting as an oxidising agent.
3) Reducing agents
Reducing agents are used to weaken the protein and have the same effect as proteases. The difference being however that the proteases will be destructed by the high temperatures in the oven while reducing agents will remain in tact of course. Reducing agents will reduce mixing time and improve dough machinability i.e. moulding will be facilitated. Reducing agents break bonds between the proteins during mixing. They have the opposite effect of oxidising agents. The most commonly used reducing agent is L-cysteine.
The functional characteristics of a protein are determined by its amino acid content. About 2 percent of the amino acid content of wheat gluten is cysteine. The amino acid cysteine contains a sulhydryl group (-SH) which can be oxidized to cystine and form a disulfide (-S-S-) bridge between two adjacent polypeptide chains or within one molecule. This is a relatively strong bond and results in an intricate and rigid network of protein molecules. The dough resulting from this oxidation will have increased gas retention, but will also be very elastic and resist flow. These doughs are often described as "bucky."
Addition of a reducing agent to dough "relaxes" the dough and gives it increased extensibility. This occurs by reducing or breaking the disulfide bonds formed between or within gluten molecules. This action serves to reduce the mixing time and less total energy is required to reach peak dough development. The time required for hydration of the starch and gluten molecules is shortened so that dough development starts earlier in the mix cycle. The rate of energy input during mixing is increased and dough development times are shortened.
Reducing agents act quickly in dough and each molecule reacts only once. The amount of gluten relaxation can be controlled by the amount of reducing agent added. Overuse of a reducing agent results in poor quality bread products. Characteristics observed include low volume, a coarse crumb texture, poor crumb colour, and a generally poor appearance.
Reducing agents common to the baking industry include L-cysteine and glutathione. L-cysteine is an amino acid and glutathione a tri-peptide.
The action of a reducing agent can be reversed and the disulfide bonds renewed through addition of an oxidant. Combination of a reducing agent with a slow-acting oxidant, such as ascorbic acid, reduces the mixing time of straight dough to be more in line with that of a sponge or liquid pre-ferment without the need for any extra equipment and space required. However, addition of a reducing agent may require an increase in floor time to achieve machinable dough, thus offsetting the gain from a decreased mixing time. Many combinations of reducing agents with oxidants are offered commercially, enabling optimization for specific situations in a bakery.
A surfactant is an amphipilic molecule. That is, one portion of the molecule has no charge (non-polar) and associates with the lipid or air phase, while another portion of the molecule is charged (polar) and associates with the water or aqueous phase of a system. These molecules migrate to the interfaces between two physical phases, with each end of the molecule associating with the preferred medium. In bread products, surfactants function less as a true emulsifier than as a surface-active agent that modifies the behaviour of the proteins and starches with which they interact. Gluten protein contains about 40% hydrophobic amino acids and interacts with the non-polar portion of surfactants.
In yeast-leavened baked goods, surfactants have been shown to strengthen the viscoelastic gluten-starch film, delay setting of the dough during baking, and to interact with starch molecules to inhibit starch retrogradation and staling.
The most commonly used emulsifiers in baking are:
The use of surfactants can increase product volume, create a fine, uniform crumb, produce a more tender crumb and crust, improve moisture retention, improve sheeting properties, and reduce staling. This paper will review a few of the more commonly used surfactants.
Some emulsifiers form complexes with the starch and slow down the retrogradation process during storage stages. Glycerol mono-stearate (GMS) is one such emulsifier possessing this property and has been used extensively in the past as a bread improver. GMS may come in a number of forms and with varying monoglyceride contents and is at its most effective against bread staling when used as a hydrate in the alpha gel form. This condition is achieved over a limited range of GMS concentrations and preparation temperatures, and careful preparation is required to ensure most effective use of this emulsifier.
Other emulsifiers that may be included for their anti-staling properties are DATA esters, and CSL or SSL. These too, have the ability to form complexes with flour components and to influence the rate at which gelatinized starch retrogrades during storage and can have an impact on reducing the staling rate.
DATA esters, CSL, and to a lesser extent, GMS, are able to play a similar role to that of fat in bread making with respect to maintaining freshness in bread.
Mono- and diglycerides are the surfactants most widely used in baking. They are esters of glycerol and one or two fatty acids. When one fatty acid is bound to glycerol it can be in either the first or the second position. The fatty acid is depicted by an "R" in the slide. These are also referred to as alpha- and beta- monoglycerides, respectively. In the production of mono- and diglycerides for commercial use, approximately 40-60% of the finished product will be monoglycerides, 30-40% diglycerides and the balance a mixture of triglycerides, glycerol and fatty acids. The alpha-monoglycerides have been described as the functionally important components and interact with amylose to inhibit recrystallisation of the starch to bring about a crumb softening effect. Propylene glycol esters of fatty acids function in much the same manner as mono- and diglycerides.
Lecithin is a naturally occurring surfactant comprised of a glycerol backbone and two fatty acids, phosphoric acid and choline. Lecithin is used in bread dough at 0.15-0.20% of the flour weight. Lecithin functions in bread dough to reduce mixing time, increase water absorption, improve machinability, yield a more uniform crust colour, a more tender crust, and to produce a softer crumb with a decreased rate of staling.
Ethoxylated mono- and diglycerides are strongly hydrophilic surfactants and function as dough strengtheners by forming strong hydrogen bonding with dough components. Use of this conditioner improves the tolerance of dough to shock in mechanized bread production.
There are no restrictions in the amount of mono- and diglycerides, propylene glycol esters of fatty acids, lecithin, and ethoxylated mono-and diglycerides that can be used in yeast-leavened baked goods, as overuse causes detrimental changes, such as an open and irregular cell structure.
Diacetylltartaric acid esters of mono- and diglycerides (DATEM) are both hydrophilic and lipophilic. They function well in dispersing shortening evenly throughout the dough, thereby improving the elasticity and extensibility of the gluten, dough handling characteristics, tolerance to mechanical shock, and improved gas retention, to yield products with greater loaf volume and a finer crumb. Diacetylltartaric acid esters of mono- and diglycerides function in a manner similar to monoglycerides to complex with starch and retard crumb staling.
Sodium and calcium stearoyl-2-lactylates are multifunctional surfactants that complex with gluten proteins and the amylose fraction of wheat starch to increase dough absorption, improve mixing tolerance and dough machinability, increase loaf volume, improve the texture of the crumb, create a more tender crust and improve shelf life. Both conditioners are limited in usage levels to less than 0.5% of the weight of flour used.