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Explore the Fermentation of Food

The Culinary Exploitation of Microbial Ecosystems

Below are some ways you can learn about fermentation in laboratory settings and through more open-ended explorations. When you like what you find, check out the full version for relevant background, full protocols, discussion questions, visuals, downloadables, and more. Adapt these materials for your context, and please reach out with suggestions and ideas!

Try with your students...

Full Testing Substrate Specificity in Yeast Fermentation

Testing Substrate Specificity in Yeast Fermentation

Full Testing Substrate Specificity in Yeast Fermentation

Materials

Corner Store: Grocery Items

  • Various sugars (try health food stores or online for the widest selection)
    • Dextrose (glucose), Galactose, Lactose, Maltose, Sucrose (table sugar)
  • Baker’s Yeast Packets or a jar

Common Items

  • Water
  • Markers

Laboratory Equipment

  • Water bath, hot plate, or pan & stove
  • Beakers or flat-bottomed bowl/baking dish
  • Timer
  • Micropipettes & tips, sterile transfer pipettes (or straws or medicine syringe)
  • 15mL Conical Tubes and a needle OR test tubes and glass slides to cover

Procedure

  1. Fill 15ml conical tube with 8ml of a sugar solution
  2. Mix the 7% yeast solution to be a uniform suspension. Fill the remainder of the tube (~7ml) with yeast solution such that the meniscus rises above the lip of the tube. 
  3. Replace cap onto tube — because of holes, there will be a small squirt of solution to come out. 
    • NOTE: make sure that there are no sizeable air bubbles in the tube
  4. Invert the tube, and place in a large beaker filled with water (preheated to 40 °C). Place this beaker into a water bath or onto a hot plate to maintain temperature 
    • NOTE: you can also test the effect of temperature on fermentation by adjusting temperature of water bath or hot plate
  5. Immediately mark the bottom of the CO2 bubble (if there is one). Mark this point at 5 minute intervals for 30 minutes.
  6. At the end of the experiment, record the level of CO2 produced at each time interval by emptying the tube, filling with water to the mark, and pouring the water into a graduated cylinder or onto a balance for accurate measurement

What conclusions can you draw about the metabolism efficiency of different substrates by S. cerevisiae?

Full Testing Substrate Specificity in Yeast Fermentation
Full Experiment with Fermentation using Kombucha

Experiment with Fermentation using Kombucha

Full Experiment with Fermentation using Kombucha

Materials

Corner Store: Grocery Items

  • Green or Black Tea Bags
  • Table Sugar (Sucrose)

Corner Store: Kitchen Items

  • Spoons
  • Jars (with loose covers)
  • 1L measuring cup or beaker
  • Thermometer
  • Hot Plate or Tea Kettle
  • Triple Beam Balance, Digital Scale, or Measuring Cup
  • Sanitizing Equipment (Dishwasher or Bleach or Starsan)

Corner Store: Specialty Item

  • Kombucha starter culture, which can come from any of the following:
    • Order a culture from an online site e.g. Etsy.com
    • Get a culture from a friend (email RockEDU 😉)
    • Use the last inch of a store-bought bottle that you like

Preparing the liquid media

  1. Clean and ideally sanitize equipment (e.g. dishwasher or chemical sanitizer—bleach, StarSan, etc.)
    • Brewing Container: 1 L container e.g. pyrex beaker, wide mouth ball jar, or measuring cup
    • Spoons (2; one for sugar, one for stirring tea)
    • Thermometer
    • Storage Container (size depends on how much broth will be left over e.g. the difference between the volume of your storage jars and 1 L; container should seal with a lid)
  2. Heat 1 L water to boiling (e.g. use an electric kettle, pot on the stove, or beaker on a hot plate)
  3. Pour ~850 ml of water into the Brewing Container. Let cool to 170F.
  4. Add 3 bags of green (or black) tea (~6g tea) and let steep for 10 minutes.
  5. Tug on bags 10 times to disperse the brewed tea. Discard tea bags.
  6. Add 150 g sucrose (table sugar; ¾ C) and stir until dissolved.
  7. Bring the water up to 1 L with the excess boiled water.
  8. Cool to room temperature (in a fridge (~30 min), freezer (keep a close eye on it), or on the counter overnight)
  9. Label the brewed tea/sugar mixture, and use to start your kombucha culture.
    • Note: this is a good stopping point as the sugar-tea can be stored for several weeks in a sealed container if good sanitation was followed.

What experimental question do you have in terms of how something might affect the production and composition of kombucha?

How will you test this?

Full Experiment with Fermentation using Kombucha
Full Yeast Fermentation Inquiry

Yeast Fermentation Inquiry

Full Yeast Fermentation Inquiry

Materials

Chemicals

  • Baker’s Yeast
  • Various Sugars (e.g. sucrose, glucose, fructose, lactose, maltose, etc.)

Gas-Collection Setup

  • Tubes or vials (e.g. 15 ml conical tubes, glass test tubes, or gas-collection vials)
  • Markers
  • Container wider than the tubes or vials to hold a bath of water
  • Water

Equipment

  • Water bath or hot plate to vary temperature
  • Timers
  • Something to move consistent volumes of liquids (Micropipettes and tips, glass pipets and bulbs, straws if need be, etc.)

Setup

Set up your tubes and water bath in such a way that the gas produced in each fermentation will rise to the tops of the tubes and volumes of gas can be marked with a permanent marker or waxed pencil.

In the example at right, plastic tubes were used with a few holes poked into each plastic cap. The tubes were filled with yeast solution and food source (e.g. glucose), covered, and inverted quickly into the water bath. The samples should be held inside the tubes and displaced into the water bath as gas is produced.

A similar setup can be used with test tubes and stoppers with holes or using a glass slide to invert each tube into the bath before sliding off the slide and allowing the fermentation gas produced to displace the yeast solution. You may also be able to use a typical gas collection apparatus from a chemistry laboratory at your school.

Finally, volumes of gas can be determined by emptying a marked tube and filling it with water exactly to the mark. Then that water can be poured into a graduated cylinder of appropriate size to determine the volume of gas produced.

Guiding the Inquiry

Think about how you can design an experiment to test this question, keeping in mind the inclusion of an appropriate control. Remember, a simple design makes for elegant results.

Write out your procedure, step by step to test your experimental question. Create a proper data table to easily record and share your results. Was your hypothesis supported by the data?  Why or why not?

Full Yeast Fermentation Inquiry

Created by

Disan Davis Disan Davis avatar

Disan is a scientist and educator striving to share her curiosity and love of science with others
RockEDU Program Manager
The Rockefeller University

Jeanne Garbarino Jeanne Garbarino avatar

Jeanne was once rescued by the FDNY after getting her head stuck in a fence. She then grew up to become a biochemist.
Director of RockEDU Science Outreach
The Rockefeller University
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