Is Lactose Necessary for Milk Fermentation? The Tale of Yogurt

Overview

Yogurt is made using a process called milk fermentation. During fermentation, bacteria break down lactose and turn it into lactic acid. This buildup of acid lowers the pH which results in the milk's proteins changing shape and sticking together, and forming the yogurt. Although the milk fermentation process breaks down lactose, yogurt still has lactose that may give symptoms to lactose intolerant adults. My hypothesis is that lactose is not essential for milk fermentation. Bacteria can also use other sugars in the milk to procedure lactic acid that results in yogurt formation. Therefore, lactose-free milk can be used to make yogurt for lactose intolerant individuals. To test my hypothesis, I used three different types of milk to produce yogurt: Regular Whole Milk, Lactose-Free Milk (Lactase treated) and Lactose-Free Milk (Ultra-filtered milk).The yogurt production steps were boiling the milk, cooling the milk down, adding yogurt bacteria, incubation at 115°F for fermentation for 1 to 6 hours, and cooling down to stop the fermentation. To analyze the formation of yogurt, pH and the consistency of the final yogurt product were assessed. The yogurt was formed with every milk type used. For all the milk types, the pH started around 6.2-6.4 and decreased to 3.9-4.0 when yogurt was formed suggesting lactic acid formation. The consistency of the yogurt was similar when regular whole milk and lactase treated lactose-free milk were used. When lactose-free ultrafiltered milk was used, the consistency of the yogurt formed slower, the yogurt was stickier and creamier than the other two types of yogurts. In conclusion, lactose is not necessary for yogurt formation. Although consistency of the yogurts can be different, using lactose-free milk to produce yogurt would make the digestion easier for those with lactose intolerance.

Competition history

• CSEF 2026 Biochemistry/ Molecular Biology (Junior Division) · Entry J-04-13

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