Complex sentence: The idea that it is served "flat" with no bubbles at all, though, is a misconception; properly conditioned cask ale contains bubbles of carbon dioxide generated by the natural action of the yeast living in the beer while it is transported and stored.
Split into simpler sentences: The idea that it is served "flat" with no bubbles at all, though, is a misconception. Properly conditioned cask ale contains bubbles of carbon dioxide generated by the natural action of the yeast living in the beer while it is transported and stored.