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Show the Fermentation of Food

Below are some ways you can show examples of fermentation in simple ways. 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!

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Full Demonstrating Live Organisms In Fermented Foods

Demonstrating Live Organisms In Fermented Foods

Full Demonstrating Live Organisms In Fermented Foods

Background

Fermented foods receive their tangy flavors, shelf stability, and possibly even health benefits from the active presence of “good” bacteria and/or yeast. Use this assay to demonstrate how fermented foods are teaming with bustling communities of microbes.

Materials

Corner Store: Grocery Items

  • Purchase (and/or make) various fermented foods, e.g.
    • fermented pickles (NOT vinegar pickles, those are different)
    • kombucha
    • yogurt
    • kimchi
photo credit: Zach Veilleux

Laboratory Items

  • Pre-poured agar plates (can be ordered online)

OR make your own using

  • Petri dishes
  • Agar powder
  • Nutrient media (e.g. tryptic soy, LB, or bacto)
  • OPTIONAL some of the fermentation medium (e.g. sweet tea for kombucha cultures)

More Laboratory Items (Household substitutes in parentheses)

  • Sterile pipette (straw, turkey baster, or medicine syringe)
  • Sterile swabs or spreaders (cotton swabs from an unopened package)
  • Test tubes or plastic tubes (skip if not available)
  • Flame or bunsen burner (candle)
  • Hot water bath or heat block (pan of boiling water)
  • Sharpie marker
  • Gloves (optional)

Procedure

Be sure to use aseptic technique, described in more detail below, while conducting all aspects of this preparation. Pre-made agar plates can be purchased from a variety of vendors, or made on your own (see recipe below).

  1. Collect the number of agar plates you will need, and label each with a sharpie marker to include your initials, date, ferment being plated, and the phrase “DO NOT OPEN”.
  2. Set up 2 tubes per ferment you plan on testing, and label each tube accordingly.
    • Tube A will be prepared at room temperature.
    • Tube B will be boiled before plating.
  3. For each ferment being tested, transfer approximately 1ml of fermentation liquid to Tube A, and 1ml of ferment liquid to Tube B.
    • Each time you go to transfer materials from the source to a tube, or from tube to tube, be sure that the transferring instrument is sanitized each time, or use a new sterile transfer pipette.
  4. Keep set A tubes on the countertop. Boil sample set B for 10 minutes by placing the tubes in boiling water or a heat block set to 100 °C.
    • by boiling the ferment, you are presumably killing all of the microbes present.
  5. Pour the liquid in each tube onto the correspondingly labeled agar plate.
  6. Spread the liquid culture evenly around the agar plate using a sterile swab or cotton swab.
  7. Return the lid to the agar plate, and allow the liquid to dry.
  8. Turn the plate upside down (so that the agar side is up) and leave on the countertop to grow for 1-4 days.
  9. Record observations, room temperature, and other factors that may be relevant.
  10. At the end of the growth period, compare the difference between Tube Set A (unboiled) and Tube Set B (boiled).

Do you notice a difference between the unboiled and boiled ferments after plating?

Full Demonstrating Live Organisms In Fermented Foods
Full Measuring the Change in pH During Lacto-Fermentation

Measuring the Change in pH During Lacto-Fermentation

Full Measuring the Change in pH During Lacto-Fermentation

Materials

Common Items

  • Water

Corner Store: Grocery Items

  • Choose one or more fermentable veggies, e.g.
    • Cucumber
    • Cabbage
    • Carrots
    • Peppers
    • Beets
    • Green Beans
  • Salt (culinary preference is Grey Celtic Sea Salt, but any table salt will work)

Corner Store: Kitchen Items

  • Jar with Lid

Laboratory Items (Kitchen substitutes in parentheses)

  • Sterile Dropper (straw, turkey baster, or medicine syringe)
  • Triple Beam Balance or Digital Scale (teaspoon measure)
  • pH Paper (can be ordered online)

Procedure

  1. Turn your sterilized jar on its side. Start loading vegetable spears into the jar, being sure that the length of vegetable pieces is shorter than the height of your jar
  2. Add approximately 20g of celtic sea salt (salt volumes vary, but if you cannot measure by weight: 5 tsp celtic sea salt, 5 tsp table salt, 6 1/4 tsp kosher salt) per pint of pickling volume (scale this if your jar volume is significantly different)
  3. Fill the jar to the very top with water.
  4. Cap it with the sanitized lid, and swish the liquid around a bit to mix the salt in.
  5. Remove the lid, and take a small drop of liquid out (using sterile dropper) and transfer to a pH strip. Record pH — this is time zero. Return lid.
  6. Continue measuring and recording pH using sterile dropper on a daily basis to understand how pH changes during the lacto-fermentation process.
  7. At the end of 2 weeks, the vegetables should be nice and crispy and ready to eat!
Full Measuring the Change in pH During Lacto-Fermentation

Created by

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

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

SSRP Students SSRP Students  avatar

Shout out to the amazing SSRP high school students who have contributed to this work through their summer research projects!
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