Exploring Traditional Mexican Fermentation: Tepache

The activity below was contributed by Clara Marcelín during our podcast interview.

Dive into the fascinating world of fermentation with this hands-on microbiology activity. Inspired by traditional Mexican beverages, Clara Marcelín shared on the Joyful Microbe podcast a unique project that introduces students to the wonders of microbial transformations through the creation of a pineapple-based fermented drink called “Tepache.” This activity not only offers a taste of culture but also provides an opportunity to observe the microbial world in action, fostering a deeper understanding of microbiological concepts.

What sets this Tepache activity apart is its tailored approach for students within a school environment. Unlike typical Tepache recipes, this version is thoughtfully designed to facilitate scientific observations and experimentation. As students embark on this journey, they not only get to savor the unique flavors of Mexican culture but also delve into the intricacies of microbial processes.

By utilizing everyday ingredients such as pineapple peels, water, and piloncillo (unrefined cane sugar), this simple hands-on fermentation experience in your classroom laboratory fosters curiosity and understanding. As the Tepache bubbles and ferments, students get a firsthand look at the transformations brought about by microorganisms, turning a traditional beverage into a living lesson in biology and chemistry.

Materials

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• Pineapple peels and a small amount of pineapple pulp
• Water
• 1/2 cup Piloncillo (Mexican unrefined sugar cones) or brown sugar
• Glass jar with lid
• Agar plates (instructions to make agar plates)
• Sterile swab
• Microscope
• pH strips

Instructions

1. Gather Ingredients: Collect pineapple peels, a small portion of pineapple pulp, water, and piloncillo (or brown sugar).
2. Prepare the Jar: Place the pineapple peels and pulp into a glass jar. Add water to cover the ingredients.
3. Add Sweetener: Break the pilloncillo into small pieces and add it to the jar. If using brown sugar, add it directly.
4. Cover the Jar: Lightly screw on a lid to allow airflow, or use cheesecloth or a fermentation lid.
5. Fermentation: Leave the jar in a cool, dark place for about 2-7 days. Check daily for changes in color, bubbles, and aroma.
6. Microbial and Chemical Observations
   1. Microscopic Observations: Take small samples of the liquid and observe under a microscope. Note any changes in microbial populations and structures.
   2. pH Measurements: Remove a small amount of the liquid and use pH strips to measure the pH of the liquid daily (make sure to measure the pH on the day you prepare the Tepache).
   3. Prepare Agar Plates: Use these instructions to make agar plates. Remove a small amount of the liquid from different stages of the fermentation process. Using a sterile loop, spread samples onto the agar plates. (You will likely need to perform serial dilutions, so read this article to learn how.)
   4. Incubate Agar Plates: Place the agar plates in an incubator at an appropriate temperature for microbial growth. Monitor the plates for colony development.
   5. Microbial Analysis: Observe the colonies on the agar plates, noting their appearance, color, and distribution. Count the number of colonies and determine the number of microorganisms present (refer to this serial dilutions article).
   6. Document and Compare: Document all observations in a lab notebook. Compare the microbial populations at different stages of fermentation.
   7. Taste Testing: If you’ve carefully taken your observations without introducing any laboratory materials (pH strips, etc.) into your Tepache and you feel comfortable doing so, after 2 days, taste the Tepache to assess its flavor and fermentation progress. Taste each day after as well. Note any changes in taste, aroma, and alcohol content. Be aware that Tepache will contain a small amount of alcohol, so tasting may not be appropriate for your purposes. However, making the chemical and microbiological observations will still provide an engaging and educational experience.

This home microbiology activity combines observation, experimentation, and cultural exploration. By creating Tepache and observing microbial changes, students gain practical insights into fermentation and microbial behavior. Additionally, this project encourages critical thinking and inquiry, opening the door to further investigations and discussions about the role of microbes in food and beverage production.