2. 1. Mixing of the dough
2. 1. 1. The mixing process
The first stage in dough processing is the mixing. During the mixing both the development of the dough and the temperature of the dough are established. If either of them or both of them are not spot on the processing and the product quality will suffer.
It cannot be stressed enough that the mixing is the most important stage of the entire process. If you do it wrong, there is no possibility to correct it later. Mixing is the only discontinuous step in an otherwise continuous process. Therefore discipline is required. I know it is not easy to repeat exactly every 12 or 15 minutes exactly the same process however it is necessary and of the utmost importance. Someone who wants to be proud of quality of the product he made, must also be proud of the fact that he is capable of repeating over and over again the same process. And that really is a challenge.
Another aspect is of course that all ingredients must be correctly weighed and that all ingredients should be added to the dough. Easy method to check whether there is yeast in the dough : put a little piece of dough in lukewarm water. After a while it should start floating, the reason being that CO2 is produced which changes the specific weight of the dough; it makes the dough lighter so it begins to float in the water.
To check whether or not there is salt in the dough, one can taste a little piece of dough to establish that the salt is there. It must also be avoided that the yeast comes in direct contact with the sugar and especially with the salt. Because of it is hygroscopic nature the salt will start to suck water out of the yeast cell (osmotic pressure) and the yeast will dehydrate, a process that can be compared with a grape becoming a raisin. If you put salt on the yeast, you will see that the salt will start to dissolve and that the mixture liquefies.
On top of that most characteristics of the final product are determined directly or indirectly during the mixing stage :
The mixing of the dough has a number of objectives :
In conventional spiral mixer, the mixing time for a dough of about 165 kg will be around 12 minutes depending such factors as the quality of the flour and the mixing method (f. i. the moment when salt is added will influence the mixing time; delayed salt addition will shorten the mixing time). During these 12 minutes one can distinguish a number of stages :
Mixing times will be influenced by :
There are a number of different types of mixers
Whatever type of mixer is used, remember that the principal aim is always the same (developing the gluten to maximum gas retention capability) but also that the type of mixer will influence – together with other mechanical actions the dough will undergo during rounding and moulding – the final structure of the crumb. And of course doughs can also be mixed by hand.
2. 1. 2. Temperature control
During the mixing process the temperature of the dough will rise due to :
The frictional heat is the result of the mechanical energy one has to put into the dough in order to overcome internal and external (dough in contact with the side of the mixer bowl) friction that is caused by the dough mixing process.
The amount of friction to be overcome is related to the water absorption and to the gluten development. As mixing time is changed, the friction factor changes as well.
The heat of hydration is the energy which gets liberated when a substance absorbs water. The amount of heat liberated varies with the degree to which water is absorbed. In the case of soluble substances, energy will be needed to dissolve them so the change in energy level is of a negative nature. So amounts of heat are withdrawn from the system.
The temperature of the dough is also influenced by other factors such as :
To cool down the dough and to remove the excess heat generated during the mixing process, the baker can use one of the following methods :
Calculation of the friction factor
Each mixer is different and each mixer will heat up a given recipe to a greater or to a lesser degree. The friction factor is defined as the value used to compensate for the temperature increase of the dough during mixing. The friction factor has to be determined experimentally i. e. a dough is made with ingredients of which the temperature is known. After the mixing process the temperature of the dough is noted. The friction factor is then calculated as follows :
3 x t°Cdough – (t°Croom + t°Cflour + t°Cwater) = friction factor
Imagine the temperature of the dough after mixing was 26°C, the room temperature 23°C, flour temperature 33°C and the water temperature was 12°C. Then the friction factor equals :
3 x 26°C – (23°C + 33°C + 12°C) = 81°C – 68°C = 10°C
Calculation of the desired water temperature
Now, once the friction factor has been determined it is easy to calculate the temperature of the water needed in order to get a predetermined dough temperature. If we want to make a dough of 25°C in a bakery where the temperature is 24°C with flour which has a temperature of 30°C, we will need water of :
(3 x 25°C) – 30°C – 24°C – 10°C = 75°C – 64°C = 11°C
The general formula is :
3 x t°Cdough – (t°Croom + t°Cflour + friction factor) = t°Cwater
Calculation of the quantity of ice needed
Imagine we have to make a dough of 24°C with flour of 35°C in a bakery where the temperature is 28°C. What would the temperature of the water be ?
(3 x 24°C) – (35°C + 28°C + 10°C) = 72°C – 73°C = - 1°C
Now water of – 1°C doesn't come through the water mains because ice is a solid. To transform water into ice we have to put in extra energy (latent heat). The change from liquid state to solid state requires quite some energy. This negative energy is liberated when we go from the solid state to the liquid state. We will use this latent heat to cool down the doughs. So the question becomes how much water do we have to replace by how much ice? Don't forget that 1 kg of ice = 1 kg of water. To calculate this, one has to use the following formula :
[kg of H2O (t°C water – calculated water temperature)]/( t°C water + 80)
We have to make a dough which contains 100 kg of flour, 62 kg of water, 2 kg of yeast and 1,8 kg of salt. The temperature of the bakery is 28°C, the temperature of the flour is 35°C and the temperature of the available water is 6°C. The desired dough temperature is 25°C. The friction factor for that particular mixer equals 18°C. How much ice would be need to achieve this temperature ?
First we have the calculate the desired water temperature :
(3 x 25°C) – (28°C – 35°C – 18°C) = 75°C – 81°C = - 6°C
The quantity of ice we need equals
62 kg x [6°C – (- 6°C)] /(6°C + 80°C) = 8,65 kg
We will need 53,3 kg of water and 8,7 kg of ice. The ice should be flaked ice in order to increase the contact surface and to facilitate the liberation of the latent heat.
Cooling down of the dough with CO2
In many bakeries the temperature of the dough is kept under control by using fine ice flakes. The following practical example gives an idea with regards to the costs of producing and using ice. For a number of doughs made with 2000 ton of flour, to get doughs of on average, about 25°C, we needed 120 tons of ice, or about 6 % of the weight op de flour. Based in the on the energy consumpiton of the equipment that produces the ice, these 120 ton cost about 2500 €. As rule of thumb we can use the following rule: to cool down 100 kg of dough, with 1°C, about 1,5 kg CO2 are needed.
CO2 is rather volatile and not withstanding the fact that it is heavier then air, i.e. it goes towards the floor of the mixing room, one has to keep in mind that humans suffocate in a room full of CO2. Moreover, the CO2 pellets cause burn marks on the skin. So a couple of precautions need to be taken when using CO2: such as aerating the mixing area and avoid contact of the pellets. The pellets should also not be stored in a closed room: they will slowly but surely evaporate and fill the room with an excess of CO2.
Theoretically the following formula canbe used to calculate the amount of pellets necessary to cool down a dough of 100 kg flour: Q = (Δt°C x kg deeg x 0,0018)/2 in which ΔT°C the differnece is between the initial temperature and the desired dough temperature. The initial temperature is measured after a few minutes the dough has been mixed at low speed.De begin. The number "2" is used when CO2 gas is used. In the case that pellets are added to the dough, the factor "3" is used. The factor 0,018 is typical for a spiral mixer and a mixing time of 12 - 15 minutes. To establish this factor a number of experiments are necessary because this factor depends on the type of mixer.
Chemical aspects of dough mixing: oxidantia & reductantia
High-speed mixers are being employed with ever increasing numbers in manufacturing allowing short-time doughs to be fully developed in less than five minutes, answering the nagging problem of meeting mixer schedules with a dough system that generally requires more mechanical development.
One version of a high-speed batch mixer can mix bread doughs in just three to five minutes. The mixer uses a mixer arm that turns at 1,750 revolutions per minute, mixes in a sealed chamber and can be tied into a programmable microprocessor for a complete computerized mixing operation.
Computerized ingredient handling (see further), including scaling of ingredients, can now make it possible to handle in bulk no-time dough concentrates and bases with automated scaling, that, was until recently, were used exclusively for major ingredients.
Much work is needed on controlled atmosphere mixing for dough development. Recent experiments on controlled atmosphere mixing suggest by controlling the type of gas blanket a dough is mixed in, the baker may be able to reduce or eliminate the use of additive maturation ingredients added to doughs.
As necessity there is certainly pressure control to meet increasing efficiency demands, cost reductions in both labour and processing, improvement of product quality and an ever-changing marketplace will continue to stimulate everyone to modernizing bakery operations-including short-time ferment systems.
The molecular entity that gives dough its cohesiveness and structure is gluten. Gluten is a tightly coiled protein that, like many other naturally occurring fibrous substances contains a substantial amount of disulfide bonds. Disulfide bonds are nature's means of giving fibrous structures strength and rigidity. One can compare that to the cross elements in a ladder or steel structure.
Oxidation of the dough
For the dough to leavened, the gluten must be relaxed i. e. the disulfide bonds must be broken. The mechanical energy imparted to the dough during mixing or dough development breaks by reduction these bonds and results in the uncoiling of the gluten molecule. Sulfhydryl (-SH) groups are formed from the sulphur of the broken linkages and the dough is free to rise or increase in volume. To maintain this new expanded "structure", the chemistry should be reversed to provide new linkages: the sulfhydryl groups must be oxidised to new disulfide bonds. This oxidation locks the new "structure" in place.
For the oxidation reaction oxygen is needed. This oxygen is partially coming form the air which is beaten into the dough, but can also be provided by oxidising agents such as ascorbic acid or calcium peroxide. Ascorbic acid however is not an oxidising agent and will first be transformed into dehydro-ascorbic acid.
The function of the oxidising agents is to oxidise the sulfhydryl groups to disulfide bonds and strengthen the dough. The result is a tightly cross linked protein structure which, following leaving, maintains a volume many times the original. Due in part to the increased strength of the gluten given by the high degree of cross-linking achieved, the dough is drier and less sticky i. e. there is an improvement in dough machinability. In addition less dusting flour is required, resulting in fewer streaks and cores in the bread. The decrease in stickiness is particularly important in highly mechanised high speed production lines.
After the gluten is mechanically uncoiled, oxidation by an oxidant helps maintain the volume gains made during the expansion of the dough by the fermentation process. The expanded dough is able to retain more permanent moisture in the final product. The extra water becomes bound within the dough structure and does not bake out of the final product. Increased water absorption results in a softer, more pliable dough with improved texture. The subsequent increases in flour yield compensates for the additional cost of the oxidising agent.
No-time doughs started in the beginning of their practical application as a method to produce breads when baked products were in short supply and the time required for baked breads from the sponge dough process or straight dough method could not meet market demands. Straight doughs were made with double the normal amount of yeast to reduce the fermentation time to a minimum. The resulting breads were saleable, but flavour was lacking and shelf life was limited. Bread quality was thought to be less than desired and short-time ferment systems were, as referred to earlier, an emergency method of bread production
Today, no-time dough systems are much more than an emergency systems for dough production. It is safe to say that a majority of retail bakers and manufacturers of hearth-type variety breads, as well as manufacturers of dough for freezing, use no-time or short-time ferment systems. The reason for a baker opting for use of a short-time ferment system is simple: time savings. In addition, equipment and space requirements are less with the short-time system; scheduling is simplified. For frozen dough operations, short-time ferment systems are the best system from a product quality and freezer stability standpoint.
Short-time ferment systems encompass a wide variety of methods from the simple to complex. Bakers now have at their disposal simple, pre-blended, short-time ferment concentrates in which all the baker has to do is add topping flour, water and yeast for ingredients. More complex systems include liquid or pre-ferments, high speed mixers and ingredients such as L-cysteine, proteolytic enzymes, oxidants, emulsifiers and a multitude of dough conditioners, many of which are part of the pre-blended concentrates. Today's use of the wide variety of no-time dough systems is due to an evolutionary process of continuous experimentation, ingredient and equipment development, and market demands. To better understand where we are today in the use of no-time dough processes, we need to understand those individual important components.
Early in the 1950's a dairy foods processing company began marketing a whey L-cysteine blend of dough conditioner that would change the way bakers view and use no-time dough systems. Use of the combination whey and L-cysteine would allow bakers to control rapid dough development uniformly to produce consistent quality bakery foods. L-cysteine is a reducing agent used to reduce the mechanical development required by yeast-raised doughs and to develop the gluten network for proper gas retention. As a review, L-cysteine works by breaking the disulfide bonds cross linking gluten strands changing to a sulfhydryl bond. The break of the cross link is considered a weakening effect and will allow the gluten to become more extensible. L-cysteine begins to work in the mixing stage of the dough development process and will continue to work until the dough is subjected to high heat during the baking process. L-cysteine will reduce required mixing time by the same mechanism to achieve a fully mechanically developed dough with less mechanical input. The greater the level of L-cysteine added to the dough, the less mixing time is required-with normal addition to yeast leavened doughs in the range of 25 to 50 ppm (parts per million).
While L-cysteine will reduce mechanical dough development requirements and yield more extensible doughs, L-cysteine does have negative side effects. The drawbacks of using L-cysteine are its weakening effect on gluten which can result in negative finished loaf characteristics, such as lower volume, dense grain and poor eating qualities. L-cysteine can affect the flour's tolerance to abuse in mixing and make-up processing, and determining the correct amount of L-cysteine can be difficult as doughs have little tolerance for higher than correct levels. Use requires care in formulation, scaling and processing. As we will discuss later, some recent research points to eliminating L-cysteine from short-time formulations because of the negative effects on dough handling and finished baked food quality. Along with the use of L-cysteine as chemical replacement for dough mechanical development, other ingredients are necessary to balance the effect of L-cysteine and to chemically replace or accelerate biochemical dough activities that were common in a straight or sponge and dough system, but are not effective during short fermentation times.
Recently a new reducing agent for batch mixed doughs has gained wide acceptance for both reducing mixing time and as a dough relaxing agent. This chemical is sorbic acid. Sorbic acid is a proven mixing time reducing agent for both yeast-leavened and chemically-leavened doughs when added in the range of 100 ppm to 2000 ppm, based on flour. Recommended levels for yeast-leavened products are at the lower end of this range.
The actual chemical changes caused by sorbic acid are not as yet well defined, but the visual benefits to the baker are: a 20 to 30 percent reduction in mixing time, a drier, more pliable dough, which does not shrink after going through the sheeter, better pan flow, particularly with hamburger buns, a less gassy dough for degassers and extruders and a finer texture in the finished bakery food.
Sorbic acid is effective in any dough system involving a kneading action in the presence of air. These processes include the sponge-dough batch process, straight-dough process, or a preferment system using batch mixing. Because of the required kneading action, sorbic acid is less effective in continuous mixing systems. Sorbic acid is effective wherever it is added, either to the sponge or dough in the batch system, to the dough in the straight-dough system, or to the pre-ferment or dough in the pre-ferment system. It should be noted, at this point, that the low level of use of these reducing agents, in the parts per million range, preclude their use in the concentrated form by most bakers. Products are available in convenient forms which make scaling a practicality for the average baker, and these forms are recommended.
The use of reducing agents can be a very important economic tool for the baker, from the following standpoint. As the need to increase production rates grows, the use of reducing agents decreases the mixing time in a batch-process mixer and the speed and/or dwell time necessary in the developer head in continuous mixing processes, thus allowing more dough to be processed in a shorter length of time. It follows, then, that the use of reducing agents substantially reduces the mixing requirements of the dough, and the production rate can be increased further.
The role of oxidation is important in the process of all yeast-raised dough manufacturing, but is even more important to the baker in a short-time ferment system because the baker, himself, must control the oxidant and oxidant type. Now because of the lack of time in processing, the baker for the first time must be keenly aware of the use and effects of oxidation in the dough system. The effect of oxidation on unleavened dough systems is basically to strengthen the dough system at various critical points in the manufacturing process. The critical points are after mixing for recovery of the dough from mechanical abuse, in the make-up stage for proper machining of the dough and during the late stage of proofing and early stage of baking for proper gas retention all of which contribute to proper finished baked product characteristics and quality. Additions of oxidation ingredients are normally greater with short-time ferment systems than that of sponge or straight doughs. As processing time is reduced, the need for added oxidation will generally increase. Oxidants can be categorized into two groups: early or fast acting and late or slow acting
Early acting reacts (azodicarbonamide, potassium iodate, ascorbic acid, calcium peroxide) in the mixing and make-up stage of production. Late acting (potassium bromate, calcium bromate) takes effect in the proofing and early baking stages and is triggered by heat and low pH. A balance of early acting along with late acting oxidation is critical in processing and finished baked goods quality. Also, and equally important, is the type and balance of early acting oxidation. Normally a blend of two or more early acting oxidants are used along with potassium bromate to meet oxidation requirements. The action of oxidation in yeast-raised dough processing is the reverse action to the L-cysteine reduction process.
Oxidants react to form or reform the cross-links of the gluten strands forming disulfide groups which act to strengthen the gluten strands and dough system for proper gas retention, volume and finished baked foods characteristics. Again, the proper use of oxidation in all dough systems, especially no-time or short-time ferment systems, is very critical. Past research has found that the required amount of oxidants added by the baker is dependent upon the fermentation time and the level of yeast in the dough system, with oxidant additions increasing with a reduction in ferment time and reduced yeast levels.
Ascorbic acid is generally recognised as safe and is very low in toxicity. Actually, it has been used by physicians as a detoxifying agent in drug poisoning. The amount added to flour for the desired mixing speed effect is so small as to have no effect on the dietary requirements of humans. Very little or virtually no vitamin C activity is retained in baked bread, because it decomposes at higher temperatures. Only about 10 percent survives baking. Ascorbic acid can be used up to 200 ppm based on flour.
Yeast or the reaction of yeast in a yeast-leavened dough does appear to act in a synergistic effect with oxidation, and minimum fermentation as little as 15 minutes can improve finished loaf qualities and reduce oxidation needs. Higher yeast levels appear to reduce the levels of oxidation added by the baker. One noted researcher investigating the subject of the effect of oxidation on yeast fermented doughs found that doughs fermented 45 minutes required six times the level of oxidation, specifically potassium bromate, than that of the control straight dough fermented for three hours.
Recent research at both Kansas State University and the American Institute of Baking have focused on the interaction of yeast with oxidant and the interaction of various types of oxidant in yeast leavened dough systems. Potassium iodate was found to be beneficial in reversing the reduction effects of L-cysteine in a short time dough system at levels of 20 ppm. With increasing potassium iodate levels to 30 ppm, lower finished loaf volume was recorded indicating additions of iodate in short-time ferment systems containing L-cysteine is both beneficial and critical in addition of the correct amount.
Degassing the dough
The art of degassing and texturising doughs is not new to the baking industry. The kneading and degassing of dough has been an important part of the bread making process. The actual means used to degas dough have varied over the years from knocking gas out by hand to mechanical "chewing up" the dough and break up the large gas bubbles, causing an even distribution of gas, or expelling the gas. The same can be said of the texturising process, which has varied from the gentle hand-kneading to the bakers' efforts to mechanically texturise doughs for better over-all quality in the final product.
There are several reasons for degassing the dough. The first and perhaps most important reason is the improved scaling accuracy achieved. The savings that can be realized by more accurate scaling of the dough pieces can play an important part when it comes to justifying the capital outlay for a new piece of equipment. Savings in dough piece weight of a couple of grams per piece can result in thousands of euro saved over the long-term life of a degassing machine.
The following graphs show how the weight varies when there is a small interruption of the dough making process. The first graph shows a standard deviation in the weight of 2,64 g. Samples taken immediately after a stop show a standard deviation 2,70 g i. e. it is not the stop by itself that will introduce more weight variation.
This last graph however shows the variation in weight after a 10 minute stop. After 5 minutes that the line was running again, the standard deviation of the weight was 2,99 i. e. that 99,5 % of all dough pieces will have a weight that varies between 68,2 g and 83,6 g.
Another reason for degassing the dough would be to increase the run time for a given batch. By de gassing the product, larger doughs can be run, since the scaling inaccuracies are minimized from the beginning to the end of the dough.
Along with running larger doughs is the advantage of being able to minimize the problem caused by short production interruptions. Where previously a short break would have caused scaling problems for the remainder of the dough, degassing the product just before the scaling function allows the dough to be processed with only minor problems.
From the standpoint of quality, a degasser improves the final product by providing a more uniform dough with which to work. This uniformity translates into improved make-up as well as better panning and more even proofing. Basically, the final product has greater uniformity, which means that it handles easier during the packaging operation. Fewer problems in packaging mean fewer rejects.
Texturising the dough
What exactly does "texturising the dough" mean ? In the baking business it means "the developing of the dough cells to form a uniform product structure. " There is, of course, more involved than just the cell structure when it comes to texturising, since strength, colour, softness and cell distribution are all related to the "texture" of the finished product. Since the term "texturising" means so much more than just cell structure to the average baker, the reasons for texturising the dough are also much more diverse
Texturising the dough can have a number of distinct advantages such as: produce uniform density, final mixing and developing, better grain structure and improved product make-up.
Since many texturising machines are fed by some type of degasser or pump (of either an auger or a lobe type), the texturising action covers up a multitude of problems created by the degassing/pumping functions. In some applications, the dough is pumped through a pipe and is damaged in the process of getting to the texturiser. The texturiser then acts as an incorporator or mixer and re-develops and disperses the dough so that there are no large pockets of damaged dough in the final product. Also, pipes tend to create larger gas bubbles and non-uniform density in the pumped dough. Texturisers will disperse the gas bubbles and present a very uniform-density dough to the scaling part of the dough processing machine.
Obviously, the two processes of de gassing and texturising cannot be completely separated but are actually overlapping processes. In dough de gassing some texturising is accomplished, and in dough texturising some degassing is obtained.
The major advantages of the two processes can be summarised simply by saying that dough improvements in the area of scaling can be realized by degassing, while texturising the dough gives a better grain structure and improves the over-all quality of the final product.