To investigate the effect of varying the masses of white sugar and yeast and the temperature on the rate of expansion of wheat dough.

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Planned Proposal:

Aim: To investigate the effect of varying the masses of white sugar and yeast and the temperature on the rate of expansion of wheat dough.

Null hypothesis: 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.

Alternate hypothesis: 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.

Apparatus:  

Proposed method:

1. Investigating the effect of mass of white sugar on the rate of rising of 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 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.

2. Investigating the effect of the mass of yeast on the rising of 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 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 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 yeast but all the other masses kept constant and the temperature kept at 27oC.

3. Investigating the effect of temperature on the rate of rising of 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/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 this mass of 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

Risk assessment:

The experiment was low risk due to non-toxic and non-hazardous nature of all substances used.  The only risk involved was the high temperatures reached by the thermostatic bath. Contact with the water in the bath was avoided since water was only 3/4th the height of the measuring cylinder.

Conclusion:

The null hypothesis stated that the rate of rising of dough would be independent of the mass of white 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 white sugar showed an increase in the rate of rising of dough as the mass of white sugar was increased. The rate of rising of dough was therefore proved positively dependent on the mass of white 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.

 

Introduction:

Yeast; we know that bakers use it to make the dough 'rise' and without it, our bread would be like flat, hard cakes. In the days when people made their own bread, they would go to a brewer and get a jug of brewer's yeast. It was fluid and yellow. Nowadays, yeast is made commercially on a large scale. The yeast used in this study was bought at a supermarket with the yellow lumps done up in paper and compressed for convenient handling. Yeast is a plant, according to the biologists, and is capable of reproducing itself. A piece of yeast consists of minute cells, with walls composed of cellulose, and an interior of living matter called protoplasm. You can feed it with a solution of sugar to make it grow, or it can be 'killed' by 'starvation' or heat.

The primary function of yeast is to supply carbon dioxide gas which inflates the dough and makes it ‘rise’. The carbon dioxide is produced as an end product of the aerobic respiration of the yeast. The polysaccharides present in the sugar are hydrolyzed into glucose, which undergoes glycolysis, a process which involves phosphorylating the glucose, to make a more active isomer, with a phosphate group from ATP, and then reduction of this isomer to form pyruvate. This pyruvate is entered into the Krebs cycle where it undergoes oxidative decarboxylation to yield hydrogen carried by the hydrogen carriers NAD+ and FAD (which are reduced), ATP and carbon dioxide. The hydrogen is entered into the respiratory chain where it yields more ATP and the ATP is utilized by the yeast as it’s universal energy carrier;it’s source of energy. Glycolysis, the Krebs cycle and the respiratoy chain constitute respiration The carbon dioxide is an waste product of respiration and is excreted.

In the dough, carbon dioxide cannot form a gas bubble on its own it requires a 'nucleating site' (i.e. somewhere it can gather to form a bubble). In fizzy drinks microscopic projections on the side of the bottle provide those sites which is why when you release the pressure as you open the bottle you see 'streams' of gas running from the sides. In bread dough the nitrogen gas bubbles trapped in the dough during mixing provide the nucleating sites; The oxygen from the air has been used up by the yeast in respiration.

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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 ...

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