How Does Salt Affect Yeast?

Objective

To determine how salt affects yeast in bread dough fermentation and its overall effect on bread quality

Background

Bread is a fermented product traditionally made from wheat flour. Essential ingredients in bread include wheat flour, water, yeast, and salt. Wheat flour is used because it contains special proteins (glutenin and gliadin) which form gluten. Gluten is unique due to its ability to stretch and bounce back. We call this its viscoelastic property. Gluten is formed when water is added to flour, and the mixture is kneaded. It is the kneading that causes the gluten proteins to combine into its viscoelastic mass to form gluten. Too much kneading, however, can cause the dough to break down and become weak. The strength of the dough will affect its ability to hold gas bubbles, which will affect bread volume. Yeast (Saccharomyces cerevisiae) is a microorganism that breaks down starch or utilizes available sugar to produce carbon dioxide gas, ethanol, organic acids, and other compounds that contribute to flavors. As CO2 is produced, it becomes trapped in the dough. During fermentation and baking, the gases expand, causing the bread to rise. Salt is added for flavor, dough strength, and to control the rate of yeast fermentation. Without salt, yeast fermentation is too fast and wild, producing large and irregular-sized air cells in the crumb structure. Rapid fermentation could also cause the fermentable sugars in the formula to be used up. With little sugar, the bread will have a pale color, since sugar is required for browning reactions such as caramelization and Maillard reaction which contribute to bread color.

Other bread ingredients and their function include: 

1. Sweetener: Provides “yeast food”; improves flavor and color; retains moisture; and improves texture
2. Fat: Adds tender texture; creates a moist mouthfeel; increases the volume
3. Dough conditioner: These are various ingredients which may include oxidizing agents to strengthen the dough, reducing agents to weaken the dough; and emulsifiers and enzymes to increase bread volume and reduce staling rate, respectively

Bread-making steps following the straight dough method include: Combining ingredients, mixing and forming the dough, fermenting, dividing and pre-shaping, intermediate proofing, shaping and panning, final proofing, cooling, and packaging. 

Materials and Equipment

1. Bread ingredients (See formulation table below)
2. Bread making machine
3. Scale (capacity = 0 – 500 g)
4. Measuring tape

Product Formulation Table

*Salt control

Method  

1. Prepare four bread machines and add the following ingredients to each:
   • Warm water at 52oC
   • Vegetable oil
   • Sugar
   • Salt (0, 6, 10, and 20 g; where 6 g is the control level)
2. All-purpose flour
3. Make a well in the flour and add the yeast
4. Bake for one hour by selecting the appropriate menu on the bread-making machine
5. Remove bread and place on a rack to cool to room temperature (a fan can be used to accelerate cooling)
6. Allow to sit in oven or cupboard for evaluation the following day

Bread Evaluation

1. Observe and record the color of the bread crust of each bread sample
2. Using a measuring tape, measure the circumference of each bread from the center, and record the value in centimeters 
3. Slice the bread and observe the distribution of air cells in the bread crumb. Note if you observe even distribution, uneven distribution, many large holes, tiny holes, etc.
4. Smell the bread to determine any differences in aroma
5. Feel the bread with your fingers to determine any difference in texture
6. Divide and taste the bread samples to determine any difference in flavor

Lab Questions

1. What are the main fermentation products of yeast fermentation in bread making? (2 points)
2. Name the specie of yeast used to make bread (1 point)
3. Name two browning reactions in bread making that give bread crust its brown color (2 points)
4. Name the two proteins that makeup gluten (2 points)
5. True or False: It is impossible to make bread without adding sugar (1 point)
6. Compare the quality of the bread samples based on your observations and explain the differences you observed. (10 points)