Video: The Effect of Temperature on the Rate of Yeast Fermentation

In which of the following temperature ranges does yeast typically produce the highest rate of fermentation? [A] 5–10℃ [B] 15–20℃ [C] 25–30℃ [D] 35–40℃ [E] 45–50℃.


Video Transcript

In which of the following temperature ranges does yeast typically produce the highest rate of fermentation? A) Five to 10 degrees Celsius. B) 15 to 20 degrees Celsius. C) 25 to 30 degrees Celsius. D) 35 to 40 degrees Celsius. Or E) 45 to 50 degrees Celsius.

Yeasts are single-celled fungi, commonly used to make bread rise or produce the alcohol and flavour in beer and wine. Fermentation is the breaking down of organic substances by enzymes. And the term is most commonly associated with the breakdown of sugars, like glucose, into ethanol and carbon dioxide. Enzymes are biological catalysts. And most enzymes are proteins.

So, what the question is really asking is, at what temperature range do biological catalysts work best? This is what the relationship between rate and temperature is for a lot of simple reactions. For instance, the reaction of hydrogen and oxygen gas forming water. However, the effectiveness of an enzyme-catalysed reaction depends on the structure of the enzyme. For instance, if this is the shape of the enzyme when it’s doing a good job, this is what it might look like if it’s overheated.

The protein is a long chain of amino acids with a complex 3D structure. If the temperature changes, the structure may change drastically, affecting how the enzyme interacts with other substances. So, while the rate of an enzyme-catalyst reaction may increase with temperature to begin with, it will decline once the temperature gets too high for the protein. So, the key is to know at what temperature, typically, enzymes start to change their shape too much. This process is known as denaturation.

The easiest way of remembering what the best temperature for enzymes is is to remember your body temperature. Your body is full of enzymes. And your body works very hard to keep the temperature at a constant value that’s ideal for the enzymes’ functions. That temperature is 37 degrees Celsius. In reality, normal body temperature varies from 36.5 to 37.5 degrees Celsius, or 97.7 to 99.5 degrees Fahrenheit. All these values lie in the range 35 to 40 degrees Celsius.

At the higher temperature 45 to 50 degrees Celsius, enzymes begin to denature, so the reaction slows down. But the other end, between five and 30 degrees Celsius, there is simply less thermal energy, so the reaction is slower. It is in the range of 35 to 40 degrees C that the reaction is given as much thermal energy as possible, while still allowing the enzymes to be effective catalysts.

There are, however, some enzymes that behave differently, with peak temperatures below 10 degrees Celsius or even above 80 degrees Celsius. However, this question pertains to ordinary yeast, which has a best operating temperature of about 37 degrees Celsius. Of course, highest rate of fermentation is not the same as best flavour. So, you’ll often see foodstuffs brewed at lower temperatures.

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