Bread is typically made by first dissolving preserved yeast (a microscopic biolo
ID: 165934 • Letter: B
Question
Bread is typically made by first dissolving preserved yeast (a microscopic biological organism that consumes sugars and emits CO2 as a waste product) in water, then adding other ingredients, including flour, sugar, fat (usually butter or shortening), and salt. After the ingredients are combined, the dough is “kneaded,” or mixed to promote the formation of a protein network from two proteins (gliadin and glutenin)15 present in wheat flour. This network is what strengthens the dough and allows it to stretch elastically without breaking. The dough is then allowed to rise in a process called “proofing,” in which the yeast consumes sugar and releases CO2, which inflates air pockets in the dough that are subsequently filled with air. Finally the dough is baked; the gas pockets expand due to the temperature rise and evaporation of water, the starches from the flour are dehydrated (dried), and the yeast dies.
A good French bread has an open, porous structure. The pores must be stabilized by the protein network until the bread is dried sufficiently to hold its shape. The bread collapses if the protein network fails prematurely.
(a)
Rouille et al.16 investigated the influence of ingredients and mixing conditions on the quality of frozen French bread dough. Each loaf was initially formed roughly as a cylinder with a mass of 150 g (including essentially no CO2), a diameter of 2.0 cm, and a length of 25.0 cm. Determine the specific volume of a bread dough proofed for two hours at 28°C from which 1.20 cm3 gas/min per 100 g dough evolves as bubbles within the dough. State your assumptions.
(b)
During proofing, the increases in volume of a series of control loaves were monitored along with the mass of CO2 evolved. Rupture of the protein network during proofing can be detected when the volume of the dough no longer increases at the same rate as the production of CO2 from the yeast. Data from one of these experiments are shown in the table below. Plot the specific volumes of CO2 (per 100 g dough) and dough as a function of time. If the preferred proofing time is such that the dough achieves 70% of its total volume before collapse, specify the proper proofing time for this formula.
(c)
The referenced study found that the parameter with the most significant influence on dough quality was mixing time, with an extended mixing time producing a stronger protein network. Why might extended mixing times not be desirable in commercial production of bread?
(d)
Suggest causes for the following undesirable bread-baking outcomes: (i) a flat, dense loaf; (ii) an overly large loaf.
(e)
Suggest why the period during which the dough rises is called “proofing.” Remember that yeast is a biological organism.
Explanation / Answer
in 1 min , = 1.2 cm3 is released
in 120 mins=
1.2* 120= 144 cm3 of carbondioxide gas is released.
144 cm3 of carbondioxide gas is released from 100g of dough
100gm of dough = 144 cm3 of carbondioxide gas
From 1 gm ,the amount of gas released is = 144/ 100= 1.44 cm3 of carbondioxide gas
Therefore from 150 grams of bread, the amount of carbon di oxide released
= 1.44 cm3 of carbondioxide gas * 150gm
= 216cm3 of carbondioxide gas
Volume of bread dough before proofin-
= volume of cylinder = r2h
= 3.14 * 12 * 25
=78.5cm3
The total volume of bread increase after 2 hours of proofing
= 78.5cm3 ( the initial volume of bread) + 216cm3 of carbondioxide gas
= 294.5 cm3
The specific volume of the loaf was calculated using the following equation (1):
Specific volume (cm3/g) =
loaf volume / loaf weight
= 294.5 cm3/150 g
= 1.96 cm3/g
b) 70% of 294.5 cm3 ( total volume of bread) = (70/100) * 294.5
= 206.15 cm3
According to the table, the time taken to achieve this volume is around 150 mins.
c)
d) causes for (i) a flat, dense loaf -
he starter was not vigorous enough, you need a lot of nice vigorous yeast to make a lofty bread. Feed your starter more often or with a higher ratio of feed.
Using a high percentage of depleted starter in a dough will obviously cause it to be denser. Bakers think, well it will be the same as feeding the starter to just make a dough, but the truth is, not only is there a low amount of vigorous yeast, but there is a high amount of gluten that has already broken down and is slack/weak. You can’t recover from a weakened gluten. Use spent starter in baked goods where lower protein (weaker flour) is used, like pancakes, muffins, pastry, cakes, etc.
Using liquid that was too hot which killed the yeast. Keep any liquid under 115F/46C
Using tap water in some areas, which may interfere with your starter and your dough.
Not refreshing your starter properly if you’ve kept it refrigerated. You might need a few feeding to get it going, especially if you haven’t used it for a while.
The dough was under or over proofed. This is the most common reason for dense bread because it can be hard at first to determine when dough is ready to bake. But both under and over fermenting can cause dense bread.
causes for (i) an overly large loaf - overproofing occurs when a fermenting dough has rested too long. Its bubbles have grown so large that they have popped and tunneled, and dough baked at this point would result in a bread with poor structure.
e) Proofing (also called proving or more rarely blooming), as the term is used by bakers, is the final rise of shaped bread dough before baking. It refers to a specific rest period within the more generalized process known as fermentation. Fermentation is a step in creating yeast breads and baked goods where the yeast is allowed to leaven the dough.