The Recipe: Make Yogurt…with Bacteria

September 26, 2022 – Yannick Bergeron, chemist


yum! Good bacteria yogurt! Does this experience make you hungry? However, yogurt is produced by bacteria. Try it !

Yogurt making equipment and ingredients:

  • coverage
  • A great deal
  • little pot
  • aluminum foil
  • wooden spoon
  • large measuring cup
  • Few mason jars
  • skimmed milk powder
  • 3.25% milk
  • cooking thermometer
  • 1 or 2 sachets of bacterial active yogurt (lactic fermentation)

Prepare homemade yogurt in 7 steps!

1. In a large saucepan, pour 1 liter of 3.25% milk and add 100 g of powdered milk. Mix well with a wooden spoon.
2. Gently heat the milk to 82°C. Monitor the temperature with a thermometer. Stir occasionally with a spoon to prevent the milk from sticking to the bottom of the pan.
3. Let the milk cool to 43°C. It takes about an hour. To save time, immerse the pan in an ice water bath. Then pour 250 ml (1 cup) of lukewarm milk into the measuring cup. Empty a bag of bacteria into the cup and mix well. Pour the impregnated milk back into the saucepan and mix.
4. Empty the skillet into the large measuring cup. Fill the jars and close them well. Clean the pan.
5. Boil the water in a kettle or saucepan. Then let the temperature drop below 45°C. This boiling water will be sterile and will maintain its temperature for a longer time. Place the mason jars in a large saucepan and cover the jars with this lukewarm water.
6. Put the lid on the pan and wrap it in aluminum foil. Then cover the pan with a blanket. Let the mixture incubate for 4 to 5 hours. During this period, the jars should not move, otherwise the milk may remain liquid. At the end of the incubation, remove the cover and aluminum foil. Refrigerate the mason jars for 8 hours.
7. Yogurt flavor with berries or granola beans. Bon appetite!

This yogurt will keep for two weeks in the refrigerator.

what’s going on ?

Bacterial cultured yoghurt bags contain two strains of bacteria: Lactobacillus bulgaricus and Streptococcus thermophilus. For them, milk is very nutritious if it is at the right temperature. Below 41 ° C, these bacteria “sleep”. Above 45 ° C they die. Between the two, these bacteria become active and feed on milk sugar and lactose and produce the waste product, lactic acid. This process is called acid fermentation.

L ‘lactic acid Contributes to the sour taste of yogurt. In addition, its acidity changes the shape of milk proteins. The result: Instead of naturally floating in the milk, the proteins clump together. Then the milk turns into a jelly: yogurt. The more protein the milk contains, the more solid the yogurt will be. For this we add powdered milk to liquid milk. The more fat the milk, the more creamy its texture.

Why heat before and after cooling? If there were other strains of bacteria in the milk before preparation began, they may also become active during the incubation period. They will disrupt fermentation by L. bulgaricus and S. thermophilus. Additionally, if some of these bacteria are harmful, we want to avoid their reproduction during incubation. Heating milk to 82°C kills these harmful bacteria and helps denature proteins. In the refrigerator, after incubation, the bacteria subside and fermentation stops. Refrigeration also helps fortify the yogurt.

Listen or re-listen to the expired (up to 7000 years) Surviving yogurt episode of The Resourceful Survival Guide podcast.


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