Question

What is it in the yeast that is specifically affected by the high heat?

Answer 1

Yeast is any various one called fungi that can cause the fermentation of carbohydrates producing carbon dioxide and alcohol.

At low temperature (0-10oc) yeast will not grow but die either. At temperature (100c-35c) yeast will grow and multiply faster at higher temperature with an optimal growth at (30 or 37oc) (that depends on the species). At higher temperature the cells becomes stressed meaning that their content becomes damaged and which can be repaired to some degree.

A high temperature (>50oc) the cells die. The Bacteria can survive freezing under certain conditions.

when baking bread all yeast dies during the process.

Most microbes such as bacteria and yeast have an optimal temperature range in which they grow best.

If it gets either too low or too high then they grow much slower and finally cease growing.

However, this temperature range can vary with different organisms.

For example, yeast grows optimally around 300c – 350c. if it rises above 400c it won’t grow at all. Below 300c, it slows down dramatically and when it gets below 10oc if really doesn’t grow much at all, so what causes this?

The main reason is the ability of the enymes that catalyze all biochemical reactions in the yeast cell to function at those temperatures.

Enzymes have an optimal temperature range. When they get below that range their ability to catalyze the intended reaction slows down. Above that temperature, the enzyme begins to denature or unfold and becomes inactive. Each enzymes will have a different range where it becomes inactive.

For an organism to stop growing at some temperature, you don’t need all the enzymes to become in active you just need one essential enzyme to stop working and then the organism fails to grow. So which ever is the first essential enzyme to get inactivated defines the maximal temperature at which that organism can grow.

some bacteria for example have becomes adapted to grow at unusual temperatures. There are thermophilic bacteria that grow in hot spring and similar places and grow fine at very hot temperatures. Some at 60 – 70 degree Celsius. A few grow above 800c or even 900c. The enzymes in this microbes have changed so that they can tolerated the high temperature.

A microbe that grows optimally at 650c may completely unable to grow at 370c.

Likewise there are some bacteria which are cold adapted and grow at very low temperatures but would be unable to grow at room temperature.