The Effect of Temperature on

Bread Yeast

Andrew Van Hoof

Background• Yeast – Active Dry Yeast• Invented in WWII to preserve

the shelf life of yeast• It is a type of dried yeast that

is activated by water.• It is placed in the bread to

cause the formation of CO2 which causes the bread to rise.

• Without the yeast the bread will not rise and create matzos.

• Since the yeast undergoes alcoholic fermentation, there is actually trace amounts of alcohol in bread.

Materials (Recipe)• 1 1/4 cups lukewarm

water• 1/4 cup vegetable oil• 1/4 cup honey, molasses,

or maple syrup• 3 1/2 cups King Arthur

Premium 100% Whole Wheat Flour

• 1 packet active dry yeast dissolved in 2 tablespoons of the water in the recipe

• 1/4 cup nonfat dried milk• 1 1/4 teaspoons salt

Independent Variable

Temperature – one bread loaf was kept at room temperature, which was 68 degrees Fahrenheit, while the other was kept at about 140 degrees Fahrenheit.

Dough at 0 Minutes

Constants• Yeast – the same active

dry yeast was used for both breads.

• Recipe timing and materials – the same ingredients and both breads were made simultaneously under the same atmospheric and room conditions.

• Both were mixed and cooked in the same type of glass cookware.

What We Did• Ingredients were combined

simultaneously so the rising process started for both breads at the same time.

• Both were kneaded by hand, and placed in a glass bowl and covered with tin foil that had a coat of oil on it to prevent sticking.

• We placed bread #2 into an oven at 140°F and placed bread #1 on the counter at 68°F.

• We let the yeast go to work.

Dough at 0 Minutes

DataBread was recorded every 15 minutes for

1.5 hours:

Dough at 0 Minutes

Dough at 15 Minutes

Dough at 30 Minutes

Dough at 60 Minutes

Dough at 45 Minutes

Dough at 75 Minutes

Dough at 90 Minutes

Data Observations• Over the course of

the 1.5 hours, we observed bread #2 rising faster than bread #1.

• Bread #2 was the bread in the oven.

• At 1.25 hours, bread #2 stopped rising, and bread #1 started to catch up to the size of bread #2.

Dough at 30 Minutes

Dough at 75 Minutes

Dough at 90 Minutes

Why Did This Happen?

• Bread rises because the yeast in the bread undergoes alcoholic fermentation, which releases carbon dioxide gas, causing it to rise.

• The yeast take glucose from the other ingredients and use it to make ATP so they can survive through glycolysis.

• There are optimum temperatures at which the yeast can process the glucose, making carbon dioxide faster, causing the bread to rise faster.

The Important Byproduct

Results• The glycolysis process that the

yeast undergoes to make energy is enzyme mediated.

• Enzymes work best at specific temperature ranges.

• Bread #2 was in that ideal temperature range for a while, but it went over that range when it was in the 140 degree oven too long and the enzymes in the bread were denatured.

• Bread #1 did not reach the optimum temperature, so it took longer for the bread to rise, yet the enzymes did not denature.

Dough at 30 Minutes

Dough at 90 Minutes

Why It Matters• When baking, bakeries

need to keep the bread in “warming rooms” so the enzymes can work at optimum temperatures, reducing the time that it takes to make one loaf of bread.

• This means that bakeries can make more bread, increasing productivity.