What are some expiremental errors in yeast fermentation lab?

the test
tube must be swirled at a steady rate to facilitate the liberation of CO2 gas from the
solution

The reaction vessel should be submerged in the water bath as far as possible to keep the
entire contents at the temperature of the water bath. There is a valve attached to the rubber stopper that should be open
while attaching the assembly to the test tube, and then closed just before the start of data collection