Kitchen chemistry: metabolism and fermentation

This is a lovely little post from Scientific Gems, a great blog with all sorts of scientific facts and ideas. If you’re interested in some light-hearted but informative science blogging, it’s recommended!

Scientific Gems

In the previous kitchen chemistry post, we discussed the metabolic process by which glucose and oxygen is converted to carbon dioxide plus water, together with a great deal of energy:

Aerobic respiration reaction

In contrast, without oxygen, only one eighteenth of the energy can be obtained, through the breakdown (glycolysis) of glucose into pyruvic acid and hydrogen atoms (which are temporarily attached to the coenzyme NAD, and must be recycled in a later stage of metabolism):

Glycolysis

In the absence of oxygen, there are two ways of taking this reaction further, and recycling the hydrogen atoms (neither alternative produces any extra energy). In our muscles (when short bursts of energy are required, as in sprinting), the pyruvic acid is converted into lactic acid. The bacteria that convert milk into yoghurt do the same thing (and it is the lactic acid which gives yoghurt its sour taste):

Pyruvic acid to lactic acid

Alternatively, in yeast, the…

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