Bread Mold Growth (Dave Farina)
Author: Dave Farina
Research Question and Hypothesis
What influence will a variety of factors have on the growth of mold on pieces of bread over a two-week period? The variables that will be tested include the presence or absence of light, the presence or absence of moisture, temperature control, and the pH of the environment.
Hypothesis 1: Mold grows faster in light than in the dark.
Hypothesis 2: Mold grows faster in wet conditions than dry conditions.
Hypothesis 3: Mold grows only at room temperature and not in the freezer.
Hypothesis 4: Mold grows only near neutral pH and not in an acidic environment.
Standards
Experimental Design
We all know what happens if you leave bread out for too long. Mold! Gross. Why does this happen, how does this happen, and are there any factors we can identify that have a measurable impact on this process?
Here are the three types of mold we may encounter in this experiment:
Rhizopus
Aspergillus
Penicillium
Independent Variable
The independent variables, which will be isolated, include light vs. dark, wet vs. dry, room temperature vs. freezer temperature, and a pH of 7 vs. 2. These will be controlled simply by setting up of the environment for each slice of bread in a specific way.
Dependent Variables
The dependent variables include mold growth, the speed of mold growth, and the type of mold growth, given that several species of mold may potentially form.
Series
This experiment will study the rate of mold growth on bread (dependent variable) as a function of a variety of independent variables, such as light, moisture, temperature, and pH.
Constants and Controls
The main constant is that each trial utilizes the same bread, and the same sample size. We can also view the dry bread at room temperature as a control, since no parameters are applied.
Materials
Sourdough bread, bread knife and cutting board, ruler, and 20+ plastic bags.
Heat lamp, dark box, water bottle, lemon juice, and smartphone camera.
Procedures
1) Unwrap the sourdough loaf, place it on the cutting board, and use the knife to cut 18 cubes from the bread with a side length of two inches.
2) Separate the bread cubes and plastic bags into 6 groups of 3. With a marker, label one group of bags as CONTROL, WET, DARK, FREEZER, LAMP, and LEMON.
3) Place one cube into each of the CONTROL bags and seal. Do the same for DARK, FREEZER, and LAMP. Do this for WET, making sure to properly dampen each cube first. Do this for LEMON as well, making sure to pour some lemon juice on each cube.
4) Place the CONTROL, WET, and LEMON bags in a safe area. Place the DARK bags in the dark box. Place the FREEZER bags in the freezer, and the LAMP bags under the heat lamp. Record the time of day when this is complete.
5) At the time of day recorded previously, record observations for each bag once per day over the next 14 days. These observations should state first whether any mold is present. If mold is present, take a clear picture with your phone, and use a ruler to estimate the surface area of the cube that is covered with mold. Lastly, state which type of mold it seems to be.
Sample Data and Graphs
Arrange data as you see fit, but be sure to include one line graph that displays the average surface area covered by mold for each category, so that quantitative comparisons can be made, as well as qualitative, in the way of documenting the day that mold first appeared.
Analysis & Conclusions
Students will most likely find that mold grows for all samples except for those in the freezer. Those at room temperature grow fastest, and the wet faster than the dry. Mold will likely be present on the cubes with lemon juice despite the pH discrepancy. This may be contrary to some of the hypotheses that many students might make. First, mold seems to grow equally well in light and dark environments, so light must not be necessary for the cellular processes of the mold. For moisture, the wet bread does indeed seem to grow mold of more varieties than the dry bread. For temperature, the bread in the freezer did not grow mold, as expected, as the temperature is insufficient for metabolic processes to occur. Contrary to expectations, pH did not have a pronounced effect on mold growth, other than potentially delaying the onset of growth. So it would seem that a variety of factors can contribute to the rate of mold growth on bread.
References