Question

the product obtained in the anaerobic respiration of yeast is

Answer 1

The primary goal of fermentation is the production of alcohol, while the goal of propagation is increasing the yeast biomass. On one hand, anaerobic yeast respiration converts sugar into alcohol, carbon dioxide, and some energy. Aerobic reparation, on the other hand, converts sugar and oxygen into water, carbon dioxide and about twenty times as much energy. The real difference between these two is that with oxygen more energy is produced. Without oxygen more alcohol is produced.

The two things that yeast need from the wort to make new cells is material (sugar) and energy. While both of these are available during both aerobic and anaerobic respiration there is much more energy during aerobic respiration. This is why a stir plate, that provides constant oxygenation, is commonly used for starters.

Oxygen is good for propagation, but how much is required, and how can it be used to maximize cell growth?

Aerobic yeast respiration is as follows:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 31 ATP (see footnote 1)
180g C6H12O6 + 192g O2 → 264g CO2 + 108g H2O + 31 ATP

Converting from moles to grams we can see that for every gram of fermentable extract 1.07 grams of oxygen are required for aerobic respiration. For a 10°P (1.040) wort that would be a whopping 107,000ppm! With pure oxygen gas the saturation point of water is only 50ppm. So in terms of aerobic respiration, there is no practical limit to the amount of oxygen that can be utilized. Oxygen, however, is toxic to yeast in high concentrations.

Answer 2

2 Ethanol, 2 molecules of ATP and 2 carbon dioxide.