Homemade yogurt may produce faster yogurt Natural yogurt with simple ingredients will be a better starter than flavored yogurt or that has several ingredients Humidity may help speed up yogurt formation and better yogurt Yogurt cannot be formed in cold climates due to low temperature

YoGurt Why Yogurt? ·         Yogurt is often called the living snack due to the presence of living culture made up of friendly bacteria - Lactobacillus bulgaricus and Streptococcus thermophilus o   The probiotics helps maintaining a healthy microbiome where large portion of the immune system resides ·         Yogurt is nutrient dense containing high amount of essential minerals and vitamins including: o   Calcium and Phosphorous o   Vitamin B12 and Riboflavin ·         Yogurt has good amount of protein and has better digestibility than milk o   Fermentation breaks down the lactose (milk sugar) into lactic acid Store Bought Yogurts - Culture Shock? Store bought yogurt is generally viewed as convenient option to get the benefits of yogurt, but in reality, they are not as beneficial nor cost effective ·         The sugar trap – many flavored yogurt, low-fat varieties contain high amount of added sugar or artificial sweeteners ·         Additives including thickeners (gelatin, milk powder, guar gum) preservatives, acidity regulators, food dyes ·         With longer shelf-life, the cultures (live bacteria) are often depleted resulting in minimal benefits ·         Higher cost typically 3x-5x compared to the equivalent cost of milk required ·         Sustainability impact as commercial yogurts uses plastics for packaging and requires refrigeration from production to store shelf, a hidden environmental cost o   Single use plastics are Homemade Yogurt – Barrier Home made yogurt offers many benefits including freshness, simple ingredients, flavor scale and being cost effective. Most importantly, if made right it will have highest amount of live cultures. However, making yogurt at home as its own challenges: ·         Starting culture ·         Contamination (ensuring bad bacteria is away) ·         Consistency and repeatability 

1. Ingredients
   • Milk type, with higher fat milk (3.25%) resulting in thick and creamy yogurt
   • Quality of culture starter (store bought vs homemade)
2. Milk preparation 
   • High heat (85-95 oC) helps sterilize the milk and breaks down whey protein 
   • Clean utensils free of bad bacteria and yeast
3. Temperature & Humidity
   • Has the biggest impact on the bacterial growth with sustained temperature between 38-42 oC being ideal
   • Humidity can help with retaining moisture and heat retention 
4. Time 
   • Shorter time (4-8 Hrs) results in mild and sweet but soft yogurt
   • Longer time (12-24 Hrs) results in acidic and tart but firm yogurt

Procedure to make yogurt

Heat milk to 100 degrees celsius on the stove Cool milk until the milk is 40 degrees Add  ½  teaspoon of culture to milk Pour into small jar Incubate in selected appliance Collect data in table Refrigerate

Jan.24,2026

Using 3% milk I made 2 bottles of yogurt with homemade culture. This is not part of the experiment and is just a check to see if it works in the bottles. I put one of the yogurt bottles in the oven and the other one outside. I started the yogurt incubation at 3:11 pm. The bottle in the oven formed into yogurt at 8:00 while the one outside never formed. The information I found was because of the cold climate we live in, the yogurt outside would take a long time to form.

Jan.25,2026

Today I am testing the thermos, the oven with the light on, and the Instant pot. Same procedure but just testing the thermos and Instant pot. The instant pot and oven with light on finished at 5:14pm  And the yogurt left yesterday was formed. The thermos has not yet formed. We are changing the appliance for the thermos.

Jan.28,2026

Today I start the real experiment. I need 12 bottles and 3 appliances. Here is the checklist.I put the yogurts in the appliances at 11:31 am. The instant pot was changed a little and affected the yogurts. The homemade oven yogurt formed at 5:34pm and The Liberte and Activia formed in the Instant pot at 6 pm and the oven at 8:03 Later the Astro formed at 8:30  in the Instant pot and 9:30 pm in the Oven.

• Heat the milk to 90 to 91 degrees celsius
• Cool the milk to 38 to 40 degrees celsius
• Wash the bottles and heat in microwave for 30 seconds
• Add culture to each bottle
• Pour milk in to bottle
• Cover with lid
• Put into appliance
• Monitor the yogurt 

Jan.29,2026

We started Test 2 and put the yogurts in the appliances at 11:58 am. The homemade thermos formed at 2:25pm today.

Jan.1, 2026

6:15 pm 8:37 pm

The Instant Pot produced the most consistent and successful yogurt. It made thick, smooth yogurt in about 2 hours and 30 minutes. The oven also worked at first, but failed on the third day, showing that it was less reliable. The thermos produced mold in all jars, meaning it was unsafe and unsuccessful. The outside environment worked, but the yogurt took much longer and was thinner.

Different yogurt cultures made different results:

• Liberté Greek yogurt made the thickest and silkiest yogurt.

• Homemade yogurt produced thick yogurt with less whey water.

• Activia and Astro produced smooth but slightly less thick yogurt.

• Flavored vanilla yogurt was less consistent and sometimes watery.

In this experiment, I learned that the appliance and the type of starter yogurt both affect how homemade yogurt turns out. The Instant Pot worked the best because it kept the yogurt warm at the right temperature. The oven also worked sometimes, but the thermos did not work and caused mold to grow. Yogurt made outside worked, but it took a long time and was thinner. I also found that different starter yogurts made different results. Greek yogurt made the thickest yogurt, and homemade yogurt had less whey water. Plain yogurt worked better than flavored yogurt. When I used yogurt again as a starter, the yogurt became thicker and smoother. My hypothesis was mostly correct. Stable heat and plain yogurt starters made the best yogurt. This experiment shows that temperature and starter type are very important for making yogurt successfully.

Application of This Project

This project shows that homemade yogurt can be successfully made using supermarket yogurt as a starter culture, even in colder climates. This has several real-world applications: 1. Cost Savings People living in cold regions (like parts of Canada 👀) can make yogurt at home instead of buying expensive packaged yogurt. This saves money over time. 2. Food Security in Cold Climates In colder areas where fresh dairy products may be harder to access, making yogurt at home provides a reliable source of nutritious food. 3. Sustainable Living Homemade yogurt reduces plastic waste from store-bought containers and supports environmentally friendly habits. 4. Understanding Fermentation Science This experiment helps students understand how bacteria work, how temperature affects microbial growth, and how fermentation preserves food.

Sources of Error

1. Temperature Fluctuations Yogurt bacteria grow best around 40–45°C. In a colder climate, the temperature may have dropped below the ideal range, slowing fermentation or affecting thickness. 2. Inconsistent Thermometer Readings If the thermometer was inaccurate or not placed properly in the milk, the recorded temperature may not reflect the true fermentation temperature. 3. Quality of Store-Bought Yogurt Starter The supermarket yogurt may have contained fewer live bacteria than expected, especially if it was old or improperly stored. 4. Contamination If utensils, containers, or hands were not fully clean, other bacteria could have affected the fermentation process. 5. Uneven Heating of Milk If the milk was not heated evenly or not cooled to the correct temperature before adding the starter, the bacteria could have been damaged. 6. Measurement Errors Incorrect ratios of milk to starter yogurt could change the fermentation results. 7. Incubation Time Differences If the yogurt was left to ferment for too short or too long, it may not have reached the expected consistency.

Title:The Science of Great Yogurt – Brod & Taylor Canada Website title:Brod & Taylor Canada URL: https://ca.brodandtaylor.com/blogs/recipes/the-science-of-great-yogurt Published year:Missing Date accessed:February 5, 2026 Contributors:Missing

Title:Plain Probiotic Yogurt | No Added Sugar Website title:Activia Canada URL: https://www.activia.ca/en/products/regular/plain/plain/ Published year:Missing Date accessed:March 4, 2026 Contributors:Missing

Title:Astro® Original Balkan Plain 3% 750 g – Astro Website title:Astro URL: https://astro.ca/products/astro-original-balkan/astro-original-balkan-plain-3-750-g/ Published year:Missing Date accessed:March 4, 2026 Contributors:Missing

Title:Liberté Greek Plain 2% Website title:Liberté URL: https://liberte.ca/en/greek/plain-2 Published year:Missing Date accessed:March 4, 2026 Contributors:Missing

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Acknowledgement

I would like to express my sincere gratitude to my dad for guiding me throughout this project and for providing valuable feedback. I would also like to thank my parents and family for supporting me and helping me gather the materials needed to conduct this experiment at home. Lastly, I appreciate the resources and information that helped me understand the science of fermentation and how temperature affects bacterial growth.