Page 117

YEAST BREADS

QUESTIONS -p. 329

1. Briefly distinguish between the following methods of bread making.
(a) Straight Dough method or Traditional Water Dissolve method.
(b) Batter method
(c) Sponge method
(d) Coolrise method or Coldough method
(e) Quickrise method

Straight Dough or Traditional Water Dissolve method: This is a common way of making bread in which all the ingredients are mixed and kneaded prior to the first fermentation period. The activation of the yeast is achieved by first starting it in warm water to which a bit of sugar has been added.
Batter method: This is a no knead method as the formula calls for different proportions of ingredients, less flour and more fat. The gluten is developed by beating rather than kneading. As the mixture is a batter, no shaping is involved, and the bread takes on the shape of the pan it is baked in. Sponge method: This is a two step method which includes a sponge stage and a dough stage. In the sponge stage, the yeast, liquid, and enough flour to make a batter are combined and left to ferment to a sponge like texture. Then the sugar, fat, and remaining flour are added to make a dough which is finished off as a straight dough, involving, kneading, bowl rising, shaping, pan rising and baking.
Coolrise method: The main difference is that the shaped dough is left to pan proof in the fridge.
Quickrise method: The yeast is added directly to the dry ingredients without prior activation. Hot liquid must be used to assure reconstitution and activation of the yeast.

2. Compare the quality characteristics of a bread produced by the following methods; Straight Dough, Coldough, Batter.

Straight Dough: The volume icreases 2 times. The crust is uniform golden brown, with a smooth top,                         definite bloom and a uniform break. The bread has a moderatefine even grain, thin                         cell walls, is moist and airy.
Cold Dough: The characteristics are similar. However, it may show signs of overproofing if not                      baked when sufficiently panproofed. This is most often seen as loaves with less bloom,                      a more compact texture, and more yeasty flavor.

Batter bread: The bread has a rougher top, a more open grain, and is coarser with moderately thick                      cell walls. It is short, tender, moist and soft.

3. Why is milk usually heated to 70°C or higher for bread making? Why is evaporated milk not heated? Should pasteurized milk be heated?

If milk is not scalded in bread making, the dough may soften during fermentation and the baked bread will have a decreased volume, open grain, and coarse texture. The scalding process kills bacteria which might interfere with regeneration of the yeast. The heat treatment also inactivates certain proteins which may have a negative effect on the yeast. Pasturized and evaporated milk needs only to be warmed not scalded as they have already been heat processed.

4. What is the optimum temperature for yeast growth? For yeast fermentation? At what stages is fermentation taking place?

The optimum temperature for yeast growth (activation) depends on the method of bread making, but for tradional water dissolved method, the range is 40°-45°C. The optimum temperature range for yeast fermentation is between 25°-30°C. Fermantation occurs primarily during the rising of the dough, although it begins when the yeast is Dehydrated and mixed with the sugar. It carries on throughout the process of rising both in the bowl and in the pan, as well as in the beginning stages of baking.

5. Why is bread dough kneaded? What are the results of underkneading? Overkneading?

The purposes of kneading are:
1) primarily to develop the gluten, which gives dough its elasticity and gas holding capacity, which in turn contribute to good volume and texture.
2) to form numerous gas cell nuclei by the inclusion of air into the dough.
3) to help distribute the yeast cells throughout the dough.
If the bread dough is under kneaded, it will be inelastic and result in a bread having a coarser grain, poor volume. If the dough is over kneaded, the dough resists rising, the gluten strands become torn and the volume of the bread is reduced. The cell walls become thick. There is probably a greater danger of under kneading than over kneading the dough.

6. What are the characteristics of both a loaf of bread that has been under proofed and one that has been over proofed? Account for these in both cases.

During proofing, CO₂ is generated which expands in the gas nuclei and stretches the gluten. The dispersion of gas during proofing is responsible for the crumb.

If the dough is underproofed the gas cells will be underinflated when the dough sets. The baked product will have thick cell walls and low volume. The tightness of the dough and inability of the cas cells to leak CO₂ causes pressure to build up as the gases accumulate and expand. As a result, the top crust separates from the lower crust with a wide tear rather than a fine shred as in dough that is light enough.
If the dough is overproofed (overinflated) when it is placed in the oven, oven spring is magnified. The baked product will have large cells, some of which will explode, giving the crumb a motheaten appearance. The top tends to flatten and balloon over the sides of the pan.

7. What are the sources of sugar for yeast fermentation?

Aside from the sugar that is usually added to activate the yeast, wheat flour itself contains approximately 1-2% sugar. It also contains amylases, enzymes which are capable of hydrolyzing starch during fermentation into dextrins and maltose. Alph-amylase attacks both amylose and amylopectic at random points in their structure, in intact starch grains, but more so in damaged or gelatinized starch granules. The random fragments of starch granule which result are soluble starch and dextrins. There is also a small amount of glucose produced. The dextrins are then susceptible to attack by beta-amylase, which can only act on damaged starch grains. The dextrins are hydrolyzed very slowly and result in the production of maltose, which is fermentable by the yeast. However, the action of betaamylase is not random, making it less effective in providing food for the yeast. Betaamylase is normally found in sufficient quantities in flour, but the levels of the more desirable alpha-amylase are low and variable. Millers test flour to ensure that there is an adequate amount of this enzyme, and if it is found to be too low, it is usually added in the form of either barley malt or fungal sources.

8. What is meant by "oven spring"?

Oven spring is the dramatic increase in volume of bread and rolls during the first 10-12 minutes of baking. As the temperature of the dough rises it becomes more fluid. The amylase enzymes are more active and the rapid conversion of starch to dextrins reduces the water holding capacity of the flour. The more fluid batter is less able to resist the pressure of expanding gases. Also production of CO₂ is accelerated and the oven heat causes the gas to expand within the cells. Oven spring is affected by the degree of proofing. (see # 11)

9. How and why does increasing the sugar affect yeast doughs? Increasing the salt? Omitting the salt?

The addition of increased amount of sugar has several effects on yeast dough.
a) Up to a certain point, an increase in the sugar proportion increases the rate of fermentation as it provides the yeast cells with a readily fermentable source of food.
b) Too much sugar, however, can have the opposit effect. By the osmotic principle, the high concentration of sugar in the medium surrounding the yeast cells limits the amount of water and nutrients that can enter the yeast cell.
c) A large amount of sugar, because of its hydroscopic nature, decreases the rate of water uptake by the flour particles, thus decreasing the rate of hydration of the gluten proteins. This results in more kneading being necessary to adequately develop the gluten.
d) The bread will brown more during baking because of the Maillard reaction and caramelization.
Salt is usually added to bread to improve flavor and affect the character of the dough. A small amount of salt reduces the rate of fermentation appropiately, allowing time for the development of flavor compounds and the strengthening of the gluten. It is said that salt has a tightening effect on the proteins, permitting them to stretch without breaking. Some salt also promotes the activity of amylases and inhibits the action of proteases which are responsible for hydrolyzing flour proteins.
Too much salt has a similar osmotic effect as excess sugar, in that it limits the amount of water and nutrients that may be taken up by the yeast cells. No salt produces a dough which is sticky and hard to handle, due to the action of proteases on the flour proteins. There is also a weakened gluten which allows overexpansion of gases during fermentation due to the extremely rapid fermentation which takes place in the absence of salt. As the dough bakes, the gas cells may rupture and result in a bread with a coarse crumb and flat flavor.

10. Why does bread dough rise during fermentation?

As the yeast cell ferments sugar, CO₂ is produced as a waste product. The fermentation reaction is as follows.

C₆H₁₂O₆----------------> 2 CO₂ (g) + 2 C₂H₅ OH

It is the CO ₂ gas which acts as the leavened, as gas bubbles of CO₂ collect in the

flour mixture. As more and more gas is generated, the volume of the dough increases, and the dough is converted to a foam. As the bubbles of gas expand, the gluten is stretched into a film surrounding the bubble.

11. Why does bread dough rise during baking? Why does it stop rising?

Bread rises during baking for the following reasons:
1) As the dough temperature rises, the amylases become more active resulting in an increased conversion of starch to dextrins. This causes the dough to become more fluid and therefore less able to resist the expanding gases.
2) The production of CO₂ gas by the yeast cells is temporarily accelerated during the first several minutes of baking.
3) The increased heat causes the gases within the dough to expand. The bread dough stops rising when it reaches an internal temperature of 60⁰ C.
This is the thermal death point of the yeast cells and the temperature at which the amylases become inactivated. Also the crumb starts to set as the starch gelatinizes and the protein coagulates.

12. What is the importance of milk or milk solids in a bread formula?

Milk increases the food value of the product as it contains proteins, fat and vitamins and minerals. It also delays staling due to the presence of the casein fraction. The milk solids contribute to the browning of the crust by the Maillard reaction.

13. What problems are involved in making refrigerator rolls? Discuss quantity of yeast, or sugar, length of storage of the dough.

Refridgerator rolls require less yeast to prevent over-fermentation during the holding period. More sugar is necessary to provide enough readily available food for the yeast as it is stored in the refridgerator. Fermentation is slow and periodic punching down is necessary to redistribute the nutrients to the yeast cells. and to release accumulating gas that may overstretch the gluten. Otherwise, the yeast cells could die and diminish the volume of the bread and the quality of the crumb. The dough must be kept covered to prevent crust formation which could cause streaks in the baked product. The dough may be stored for up to 4 days in the refridgerator.