During the process of dough rising the carbon dioxide goes into solution until the solution is saturated and then any more which is generated makes its way into the nitrogen gas bubbles which grow in size and the dough expands. The more yeast and the warmer the temperature the faster the expansion – maximum production of gas occurs at 40-45oC.
Dough Development
Dough development is a relatively undefined term. Among other things, it addresses a number of complex changes in bread ingredients that are set in motion when the ingredients first become mixed. The changes are associated with first the formation of gluten, which requires both the hydration of the proteins in the flour and applied energy. The role of energy in the formation of gluten is not always fully appreciated. It is often erroneously associated with particular breadmaking processes, especially those which employ higher speed mixers.
Initially, gluten is formed when flour and water are mixed together. The proteins in the flour, glutenin and gliadin cross link, using the water as a vehicle to form gluten. Enhancing this gluten structure is important relative to developing a gas retaining structure in the bread. (Corriher) Energy is provided through the process of kneading. Simply put, gluten does not form spontaneously in that energy must be provided for its formation. There is no spontaneous combustion…at least not in breadmaking.
Cell Creation and Control Thereof in the Dough
The production of a defined cellular structure in the baked bread depends entirely on the creation and retention of gas bubbles in the dough. After mixing has been completed, the only 'new' gas which becomes available is the carbon dioxide gas generated by the yeast fermentation. Carbon dioxide gas has many special properties. At this point we are concerned with two: its high solubility and its relative inability to form gas bubbles. As the yeast produces carbon dioxide gas, the latter goes into solution in the aqueous phase within the dough.
If the carbon dioxide does not form its own gas bubbles how then does expansion of the dough through gas retention occur? Two other gases are available in significant quantities within the dough as a result of mixing. These are oxygen and nitrogen, both of which are derived from any quantities of air trapped within the dough matrix as it forms. In the case of oxygen, its residence time in the dough is relatively short since it is quickly used up by the yeast cells within the dough Indeed so successful is yeast at scavenging oxygen that in some breadmaking processes no oxygen remains in the dough by the end of the mixing cycle. Thus, the bread fermentation process is referred to as an anaerobic, alcoholic fermentation brought about by fermenting agents present in the dough, The rapid loss of oxygen from mechanically developed doughs has been illustrated previously for a wide range of nitrogen to oxygen ratios
With the removal of oxygen from the dough, the only gas that remains entrapped is nitrogen. Nitrogen plays a major role by providing bubble nuclei into which the carbon dioxide gas can diffuse as the latter comes out of solution. The number and sizes of gas bubbles available in the dough at the end of mixing will be strongly influenced by the mechanism of dough formation and the mixing conditions in a particular machine. The effects of mixer design are very important, but this is not within the scope of this presentation. At this stage it is only necessary to register the significant role that mixing will play in the creation, and/or manipulation of dough bubble structures.
Osmotic Pressure
The osmotic properties of a yeast cell are due to selective permeability of the cell wall with regard to solutions. This selectivity plays an important role in controlling the movement of nutrients into a cell. Nutrients are present in a medium in the form of ions, sugar, and amino acids. The permeability of the cell wall also permits the release of alcohol and carbon dioxide from the cell during fermentation.
High concentrations of sugars, inorganic salts, and other solubles inhibit yeast fermentation as a result of effects produced by high osmotic pressures. Basically, all fermentable sugars begin to exert an inhibiting effect on yeast when their concentration exceeds about 5% in the dough, with the degree of inhibition becoming progressively greater as the concentration of the sugar rises. This inhibitory effect is more pronounced with such sugars as sucrose, glucose and fructose than with maltose. The last sugar is a disaccharide that persists as such in the fermenting medium, and therefore exerts a lower osmotic pressure than the monosaccharides and the readily hydrolyzed sucrose, The sensitivity of yeast to osmotic pressure varies with different yeast strains, with some being better suited than others for fermenting sweet doughs with their high sugar contents.
Salt exerts a similar osmotic effect, except that some fermentation inhibition appears to set in at concentrations below the normal 2.0% level. A decrease in gas production occurred over a four (4) hour period when the concentration of sodium chloride was increased from 1.5 to 2.5% in a straight dough. One percent (1%) salt, based on flour, exerts an osmotic effect that is equivalent to that of 6% glucose.
Salt in concentrations over 1.5% exerts an inhibitory effect on yeast activity, either by its osmotic pressure or by a specific chemical effect. For this reason, salt is generally withheld from the sponge in the sponge-and-dough process. Interestingly, it has been shown that at lower levels, rather than being detrimental, salt actually exerts a favorable influence on yeast fermentation, A series of studies have shown that the use of 0.5 to 1.0% salt in the sponge of a sponge-and-dough process resulted in reductions in the fermentation time, while at the same time producing a better quality bread than was obtained with a sponge containing 0.15% or no salt.
The Fermentation Process
Please note that the majority of scientific data available to us regarding sponge and dough fermentation is found in Baking Science and Technology by E. J. Pyler. He describes sponge and dough as follows: "In the sponge-and-dough method, the major fermentative action takes place in a preferment, called the sponge, in which normally 50 to 70% of the total dough flour is subjected to the physical, chemical, and biological actions of fermenting yeast. The sponge is subsequently combined with the rest of the dough ingredients to receive its final physical development during the dough mixing or remix stage…. Sponge consistency may vary from stiff to soft or slack, depending on the baker's over-all expectations regarding its influence on final product quality".
As bakers know, before any dough can yield a light, aerated loaf of bread, it must be fermented for a sufficiently long time to permit the yeast to convert the assimilable carbohydrates into alcohol and carbon dioxide as the principal end products.
The most apparent physical change marking the course of fermentation in a dough is the steady increase in the volume of the dough mass. The sponge expands to four to five times its original volume before it recedes, assuming at the same time a light, spongy character. The findings described in Pyler relative to the gassing power of yeast action on carbohydrates are interesting and of value to the baker. For example, if 100 lb of flour will yield approximately 180 lb of dough, the degree of expansion in the dough during fermentation and proofing can be sustained by about 3.5% of fermentable carbohydrates, based on flour. Part of these carbohydrates may be comprised of the native sugars of flour, part may result from alpha-amylase action on damaged starch, and part may comprise added sugar. Any sugar over and beyond the 3.5% level will show up as residual sugar in the finished bread.
In bread baking, fermentation occurs due to a conversion of sugars (technically, glucides or sugars, naturally present in the flour) to alcohol and carbon dioxide under the effect of commercial or naturally occurring yeast and bacteria. This is categorized as alcoholic fermentation. Figure 3 outlines some of the basic chemical reactions which occur during fermentation. Not included in this schema is the conversion of sucrose to glucose and levulose by the enzyme invertase. Glucose and levulose are then subsequently converted to carbon dioxide and ethanol by zymase in the reaction shown in the Figure 3.
Sugar Transformations (Rosada)
Simple sugars: The main simple sugars, glucose and fructose, represent about 0.5% of the flour. Yeast can directly assimilate them by penetration of the cell membrane. Simple sugars are transformed into alcohol and carbon dioxide by zymase, an enzyme naturally present in yeast cells. Because of this easy absorption, these sugars are the first ones used in the fermentation process. Their consumption takes place during the first 30 minutes or so at the beginning of the fermentation process.
Complex sugars: The two main types naturally present in flour, saccharose and maltose, represent approximately 1% of the flour. Because of their complex composition, these sugars will be used later on in the fermentation process. The lapse of approximately 30 minutes at the beginning of the fermentation period is necessary to achieve their enzymatic transformation into simple sugars. The enzymes involved are saccharase, which transforms saccharose into glucose and fructose, and maltase, which transforms maltose into glucose.
Very Complex sugars: The main very complex sugar is starch, which represents about 70% of the flour content. Two types of starch are found in flour: amylose and amylopectin. Amylose is degraded by the enzyme beta amylase into maltose, and in turn the maltose will be degraded into glucose by the maltase enzyme. Amylopectin is degraded by the alpha amylase enzyme into dextrin, after which the dextrin is degraded by the beta amylase into maltose. This maltose will them be degraded by the maltase into glucose.
The simple sugar, glucose, obtained during these transformations is used by the yeast to generate carbon dioxide and alcohol. During the fermentation process, most of the starches used are the ones damaged during the milling process. Because the particles are damaged, they can easily absorb water during the dough making process. This water contact triggers the enzymatic activity. A non-damaged particle of starch will only retain water at its periphery and not inside the particle itself.
Abstract:
The aim of this experiment is to investigate the effect of varying the mass of white sugar and yeast and varying the temperature on the rate of rising of dough. The recipe for dough used in this study is 75,000mg of flour,2,000mg of white sugar and 2,000mg of yeast. These were weighed separately into separate weighing boats on a mettler balance. The white sugar was quantitatively poured into a 250ml beaker and dissolved in 25ml of glass-distilled water added quantitatively using a 25ml measuring cylinder. The white sugar was dissolved completely by stirring with a glass stirring rod. The 2,000mg of yeast was then added quantitatively to this mixture and the volume made up to 100ml with glass distilled water. The mixture was left to stand for exactly for 5 minutes and the bubbles observed indicated ongoing fermentation. The 75,000mg of flour was then quantitatively added to the yeast/sugar solution and thoroughly mixed with a glass stirring rod until a semi-liquid dough or slurry was formed. This slurry was carefully poured into a 100ml measuring cylinder till it’s top reached the 30ml mark. The measuring cylinder was placed vertically placed into a thermostatic water bath at 27oC with the water covering at least ¾ of the measuring cylinder. The stopwatch was immediately started and the volume the dough had reached was recorded every minute for 15 minutes. This procedure was repeated again for the aforementioned mass of white sugar and then twice for 0, 4000, 6000, 8000 and 10000mg of sugar to investigate the effect of varying mass of white sugar. The temperature was kept constant at 27oC. To investigate the effect of the mass of yeast, the procedure was repeated twice for the masses 0, 2000, 4000, 6000, 8000 and 10000mg of yeast. The temperature was kept constant at 27oC. To investigate the effect of varying the tempearature, the procedure was repeated using 75,000mg of flour,2,000mg of white sugar and 2,000mg of yeast but with the thermostatic water bath set at 15, 35, 45, 55 and 65oC. For each temperature, the experiment was done twice. The volume of dough every minute for 15 minutes was recorded in a table for each variable and the rate of rising of the dough calculated with the equation- Rate= volume(in ml)/time (seconds). 3 graphs were plotted, for mass of white sugar, mass of yeast and temperature. The graphs were plotted with rate of rising of dough on the y-axis and the variable(mass of white sugar, mass of yeast or temperature) on the x-axis.
The results obtained showed a positive dependence of the rate of rising of wheat dough on the mass of white sugar. A positive dependence of the rising of wheat dough on the mass of yeast was also established. The rate of rising positively depended on the temperature up to 35oC after which a rise in temperature was shown to decrease the rate of rising of wheat dough.
The null hypothesis stated that the rate of rising of wheat dough would be independent of the mass of white sugar, the mass of yeast and the temperature. The results obtained proved the null hypothesis wrong and concise relationships set up between the rate of rising of wheat dough and the mass of white sugar, mass of yeast and the temperature.
1.0 Method/Implementing:
1.1. Investigating the effect of mass of white sugar on the rate of rising of wheat dough.
75,000mg of flour, 2,000mg of white sugar and 2,000mg of yeast were weighed separately into separate weighing boats on a mettler balance. The white sugar was quantitatively poured into a 250ml beaker and dissolved in 25ml of glass-distilled water added quantitatively using a 25ml measuring cylinder. The white sugar was dissolved completely by stirring with a glass stirring rod. The 2,000mg of yeast was then added quantitatively to this mixture and the volume made up to 100ml with glass distilled water. The mixture was left to stand for exactly for 5 minutes and the bubbles observed indicated ongoing fermentation. The 75,000mg of flour was then quantitatively added to the yeast/white sugar solution and thoroughly mixed with a glass stirring rod until a semi-liquid dough or slurry was formed. This slurry was carefully poured into a 100ml measuring cylinder till it’s top reached the 30ml mark. The measuring cylinder was placed vertically placed into a thermostatic water bath at 27oC with the water covering at least ¾ of the measuring cylinder. The stopwatch was immediately started and the volume the wheat dough had reached was recorded every minute for 15 minutes. This procedure was repeated again for this mass of sugar and then done twice for the repetitions using 0, 4000, 6000, 8000 and 10000mg of white sugar but all the other masses kept constant and the temperature kept at 27oC.
1.2. Investigating the effect of the mass of yeast on the rising of wheat dough.
75,000mg of flour,2,000mg of white sugar and 2,000mg of yeast were weighed separately into separate weighing boats on a mettler balance. The white sugar was quantitatively poured into a 250ml beaker and dissolved in 25ml of glass-distilled water added quantitatively using a 25ml measuring cylinder. The white sugar was dissolved completely by stirring with a glass stirring rod. The 2,000mg of yeast was then added quantitatively to this mixture and the volume made up to 100ml with glass distilled water. The mixture was left to stand for exactly for 5 minutes and the bubbles observed indicated ongoing fermentation. The 75,000mg of flour was then quantitatively added to the yeast/white sugar solution and thoroughly mixed with a glass stirring rod until a semi-liquid dough or slurry was formed. This slurry was carefully poured into a 100ml measuring cylinder till it’s top reached the 30ml mark. The measuring cylinder was placed vertically placed into a thermostatic water bath at 27oC with the water covering at least ¾ of the measuring cylinder. The stopwatch was immediately started and the volume the wheat dough had reached was recorded every minute for 15 minutes. This procedure was repeated again for this mass of white sugar and then done twice for the repetitions using 0, 4000, 6000, 8000 and 10000mg of yeast but all the other masses kept constant and the temperature kept at 27oC.
1.3. Investigating the effect of temperature on the rate of rising of wheat dough.
75,000mg of flour, 2,000mg of white sugar and 2,000mg of yeast were weighed separately into separate weighing boats on a mettler balance. The white sugar was quantitatively poured into a 250ml beaker and dissolved in 25ml of glass-distilled water added quantitatively using a 25ml measuring cylinder. The white sugar was dissolved completely by stirring with a glass stirring rod. The 2,000mg of yeast was then added quantitatively to this mixture and the volume made up to 100ml with glass distilled water. The mixture was left to stand for exactly for 5 minutes and the bubbles observed indicated ongoing fermentation. The 75,000mg of flour was then quantitatively added to the yeast/white sugar solution and thoroughly mixed with a glass stirring rod until a semi-liquid dough or slurry was formed. This slurry was carefully poured into a 100ml measuring cylinder till it’s top reached the 30ml mark. The measuring cylinder was placed vertically placed into a thermostatic water bath at 27oC with the water covering at least ¾ of the measuring cylinder. The stopwatch was immediately started and the volume the wheat dough had reached was recorded every minute for 15 minutes. This procedure was repeated again for this mass of white sugar and then done twice for the repetitions using temperatures of 15, 35, 45, 55, 65oC but all the masses of the constituents kept constant.
Controlled variables:
1. Temperature was kept at a constant 27oC except for the experiment for which temperature was the variable being investigated.
2. The mass of flour was kept constant at 75,000mg.
3. The time the yeast/white sugar solution was left for fermentation to occur was kept constant at five minutes.
Possible sources of error:
- The time taken to stir when dissolving the white sugar, yeast and flour was not constant. These times varied and might have contributed an error to the experiment.
-
The water of the thermostatic water bath covered 3/4th the height of the measuring cylinder so above that height the dough’s temperature was lower than that of the water bath. This could have affected the values for the investigation into the effect of the temperature on the rate of rising of the wheat dough since the measuring cylinder was not fully immersed.
Precautions:
1. Contact with the water in the thermostatic water bath was avoided at all temperatures above 27oC to avoid any damage to skin by heat.
Table of results:
MASS OF WHITE SUGAR
0mg of white sugar:
2000mg of white sugar:
4000mg of white sugar:
6000mg of white sugar:
8000mg of white sugar:
10,000mg of white sugar:
MASS OF YEAST
0mg of yeast
2000mg of yeast:
4000mg of yeast:
6000mg of yeast:
8000mg of yeast:
10000mg of yeast:
TEMPERATURE
11oC:
27oC:
35oC:
45oC:
55oC:
65oC:
Analysing evidence:
Rates of rising of wheat dough for the different masses of white sugar:
The graph of rate of rising against mass of white sugar had an overall positive gradient; the rate increased as the mass of sugar increased. The peak rate of rising of wheat dough (0.041 ml/sec) corresponded to the highest mass of white sugar (10,000mg). This trend implies a positive dependence of the rate of rising on the mass of white sugar.
The rate of rising of dough was 0.012 ml/sec when the mass of white sugar was 0mg. This implies that the yeast can respire aerobically without the presence of white sugar for 15 minutes or more.
As the mass of white sugar rose from 0mg to 2000mg, the slope of the graph rose steeply due to the sharp rise of the rate, from 0.012 ml/sec to 0.023 ml/sec, with the rate when the mass was 2000mg being almost double that at 0mg. When the mass was raised to 4000mg, the slope became gentler indicating the small change on rate from 0.023 ml/sec to 0.027 ml/sec. The slope continued to rise in this gentle manner as the mass rose to 8000mg and then became comparatively more steep when the mass rose to 10,000mg indicating the rise of the rate from 0.038 ml/sec to 0.041 ml/sec. The steepest slope was the increase in the mass of sugar from 0 to 2000mg.
Rates of rising of wheat dough for the different masses of yeast:
The graph of rate of rising of wheat dough against mass of yeast had an overall positive gradient: the rate increased as the mass of yeast increased. This indicates a positive dependence of the rate of rising of wheat dough on the mass of yeast. The mass of yeast was also shown to be crucial to the rate of rising of dough since the rate when the mass was 0mg was 0 ml/sec.
The rate rose steeply to 0.023 ml/sec as the mass of yeast increased to 2000mg. The graph kept on rising with an almost equal slope as the mass rose from 2000mg up to 8000mg. The difference in the rate from 2000mg to 4000mg was 0.015 ml/sec, from 4000-6000mg was 0.012 and from 6000-8000mg, 0.015 ml/sec. This would have been a constant rise in rate had it not been for the rate increase from 4000-6000mg being slightly smaller than the aforementioned other two increases. The slope became gentler as the mass was increased to 10,000mg due to the comparatively low difference in rate of 0.006 ml/sec. This was the smallest rise in rate for the investigation into the effect of the mass of yeast. The steepest rise in rate was the rise when the mass of yeast was increased from 0mg to 2000mg; increase was 0.0023 ml/sec.
Rates of rising of wheat dough for the different temperatures:
The graph of rate of rising of wheat dough against temperature primarily has a positive gradient and then a negative one. The rate at 15oC was 0.003 ml/sec. When the temperature was increased to 27oC, an almost doubling of the temperature, the rate rose sharply to 0.023 ml/sec. Wen the temperature was increased to 35oC the rate rose sharply again to 0.055 ml/sec. The increase in rate from 27oC to 35oC (0.0227 ml/sec) was greater than that from 15oC to 27oC (0.032 ml/sec).The rate dropped steeply when the temperature was increased form 35oC to 45oC. From here onwards, the slope of the graph proceeded negatively, implying that after 35oC the rate of rising of dough is negatively dependant on the temperature. From 45oC to 65oC the gradient of the graph dropped almost uniformly corresponding to the close differences in rates as the temperature was increased; Decrease in rate from 45oC to 55oC was 0.010 ml/sec whilst that from 55oC to 65oC was 0.009 ml/sec.
The peak rate on the graph was at a temperature of 35oC corresponding to the peak rate of 0.055 ml/sec. The two lowest rates were at the temperatures 15oC and 65oC, the lowest and the highest temperature respectively. The rate at the temperature of 15oC(0.003 ml/sec) was lower than that at 65oC (0.016 ml/sec).
The graph obtained of both mass of white sugar and mass of yeast against the rate of rising of wheat dough showed considerable differences between the effects of the mass of white sugar and the mass of yeast on the rate of rising of wheat dough. Overall, the mass of yeast proved to be the more contributing factor affecting the rate of rising of dough; raising the mass of both white sugar and yeast resulted in a rise in the rate of rising of wheat dough but overall a mass of yeast caused a higher rate of rising than an equal mass of white sugar. This was shown with the masses of 4000-10,000mg of both white sugar and yeast; 4000mg of white sugar yielded a rate of rising of 0.027 ml/sec whilst it yielded a rate of 0.038 ml/sec for an equal mass of yeast. The anomalies were the rates yielded for the masses 0 and 2000mg of white sugar and yeast. The rate of rising of the wheat dough was ml/sec for 0mg of yeast but 0.012 ml/sec for 0mg of white sugar. This result was abnormal since the general trend was the rate of rising being more for a given mass of yeast than for an equal mass of white sugar. At a mass of 2000mg,of both white sugar and yeast, the two lines of the two variables on the graph intercepted; this was due to the rates of rising of wheat dough being equal (0.012 ml/sec) for 2000mg of both sugar and yeast. As the masses of both white sugar and yeast increased above 2000mg, the difference in rates of rising for the masses of white sugar and yeast got larger; the difference was 0.011mg/ml for 4000mg of both sugar and yeast, 0.018 ml/sec for 6000mg of both white sugar and yeast, 0.027 ml/sec for 8000mg of both white sugar and yeast, and 0.030 ml/sec for 10,000mg of both sugar and yeast.
The peak rates of rising for both investigations of the effects of the masses white sugar and yeast on the rates of rising of wheat dough were at their maximum masses, 10,000mg.
Statistical analysis:
The Spearman Rank Correlation Coefficiant,rs was used to determine the degree to which the variables investigated affected the rate of rising of wheat dough. The formula used for calculating rs was:
rs= 1-(6∑d2)
(n3-n)
Rates of rising of wheat dough for the different masses of white sugar:
rs= 1-(6 x 0)
(63-6)
= 1.0
The Spearman Correlation Rank Coefficient, rs, calculated to determine the dependence of the rate of rising of wheat dough on the mass of white sugar was 1.0. This value is positive and hence shows a positive correlation of the rate of rising of wheat dough on the mass of white sugar. The value, 1.0 signifies a perfect correlation. Hence, a perfect positive correlation has been proved and hence the above stated positive dependence of the rate of rising of wheat dough on the mass of sugar is accepted.
Rates of rising of wheat dough for the different masses of yeast:
rs= 1-(6 x 0)
(63-6)
= 1.0
The Spearman Correlation Rank Coefficient, rs, calculated to determine the dependence of the rate of rising of wheat dough on the mass of yeast was 1.0. This value is positive and hence shows a positive correlation of the rate of rising of wheat dough on the mass of yeast. The value, 1.0 signifies a perfect correlation. Hence, a perfect positive correlation has been proved and hence the above stated positive dependence of the rate of rising of wheat dough on the yeast is accepted.
Rates of rising of wheat dough for the different temperatures:
rs= 1-(6 x 28)
(63-6)
= 0.2
The Spearman Correlation Rank Coefficient, rs, calculated to determine the dependence of the rate of rising of wheat dough on the mass of white sugar was 0.2. This value is positive and hence shows a positive correlation of the rate of rising of wheat dough on the temperature. The value though, 0.2, signifies a weak correlation. Hence, even though the correlation is positive, it is weak signifying the rate of rising of wheat dough doesn’t necessarily depend on the temperature. This value is due to a positive correlation of the rate of rising of wheat dough up until 35oC. From 45oC, the correlation is negative. The Spearman Rank Correlation Coefficient cannot be calculated for 11-35oC and then 45-65oCbecause this statistical test s inappropriate for 3 pairs of observations. Hence the initial assumption, that the rate of rising of wheat dough initially, up to 35oC, positively depends on the temperature and then, after 45oC, negatively depends on the temperature.
a perfect positive correlation has been proved and hence the above stated positive dependence of the rate of rising of wheat dough on the mass of sugar is accepted.
Discussion and evaluation:
The raw results obtained for the investigation into the effect of the mass of white sugar on the rate of rising of wheat dough showed that as the mass of white sugar was increased, the final volume of wheat dough increased. The rate of rising calculated from the raw results showed the rate of rising of wheat dough increased with increasing mass of white sugar. The statistical test used, the Spearman Rank Correlation Coefficient proved a perfect positive correlation of the rate of rising of wheat dough to the mass of white sugar.
The raw results obtained for the investigation into the effect of the mass of yeast on the rate of rising of wheat dough showed that as the mass of yeast was increased, the final volume of wheat dough increased. The rate of rising calculated from the raw results showed the rate of rising of wheat dough increased with increasing mass of yeast. The statistical test used, the Spearman Rank Correlation Coefficient proved a perfect positive correlation of the rate of rising of wheat dough to the yeast.
The raw results obtained for the investigation into the effect of the temperature on the rate of rising of wheat dough showed that as the temperature was increased from 11oC to 35oC, the final volume of wheat dough increased. From 45oC to 65oC though, as the temperature was increased, the final volume of wheat dough decreased. The rate of rising calculated from the raw results showed the rate of rising of wheat dough increased with increasing temperature up to 35oC. The rate of rising dropped with increasing temperature from 45oC to 65oC. The statistical test used, the Spearman Rank Correlation Coefficient proved a weak positive correlation of the rate of rising of wheat dough on the temperature. The results for the statistical test showed increasing the temperature didn’t necessarily result in an increase in the rate of rising of wheat dough.
Hence the raw results, analysis of those results and the statistical test proved that the null hypothesis, which stated that the rate of rising of dough will be independent of the mass of white sugar and yeast present in the dough and independent of the temperature should be discarded. The alternate hypothesis, which stated that the rate of expansion of the wheat dough will be positively dependant on the masses of the white sugar and yeast and the dependence on the temperature will initially be positive, and then negative, was proved correct.
The white sugar used in this investigation contains sucrose. This sucrose was broken down by the yeast into glucose, which was then used as the food source in respiration to produce ATP, the universal energy carrier. One of the end products of the respiration is carbon dioxide, the gas responsible for the rising of dough. The more food there is, the more it can be used to produce ATP, with the excretion of carbon dioxide. The dough rose even when the mass of sugar was 0g. This was due to food stores within the yeast. These food stores enabled the yeast to respire for at least 15 minutes, producing carbon dioxide and hence making the dough rise.
During the investigation into the effect of the mass of yeast on the rate of rising of wheat dough, a positive dependence of the rate of rising on the mass of yeast was established. All the investigations involving yeast were done with 2000mg of white sugar; the yeas
Suggestions for further investigations:
Intermediate temperatures between the ones used in this study could be used when investigating the effect of temperature on the rate of rising of wheat dough. The temperature with the maximum rate in this experiment was 35oC and the next temperature investigated, 45oC, showed a drop in the rate of rising of the wheat dough. The optimum temperature was therefore assumed to be 35oC. A further investigation could investigate the rate of rising of the wheat dough at 40oC to determine whether 40oC yields a higher rate. Intermediates would give a more accurate graph and hence a better relationship between rate of rising of wheat dough and temperature would be attained.
White sugar was used in this study. Further investigations could compare the rate of rising using equal masses of white sugar and brown sugar
Conclusion:
The null hypothesis stated that the rate of rising of dough would be independent of the mass of sugar and yeast present in the dough and independent of the temperature. The results obtained proved the null hypothesis wrong; the graph obtained of rate of rising of dough against mass of sugar showed an increase in the rate of rising of dough as the mass of sugar was increased. The rate of rising of dough was therefore proved positively dependent on the mass of sugar. The graph obtained of the rate of rising of dough against the mass of yeast showed an increase in the rate of rising of dough as the mass of yeast was increased. The rate of rising of dough was therefore proved positively dependent on the mass of yeast.
The graph of rate of rising of dough against temperature showed two relationships; a positive dependence of the rate of rising of wheat dough on temperature up to 35oC and a negative dependence of the rate of rising of wheat dough on temperature from 45oC onwards.
Therefore to obtain maximum rising of dough, a high mass of sugar, a high mass of yeast and a temperature of 35oC will be needed.
References:
1. D.J Taylor, N.P.O Green, G.W. Stout: Biological Science
Volume 1 > 2
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5.http://www.theartisan.net/dough_development.htm