Re: Sugar's a start
Yeast are eukaryotes like us. A higher form of life than bacteria. Cells with a central nucleus and mitochondria for energy production and oxygen chemistry. The evolution of Eukaryotic life (bacteria are prokaryotes) was a blink in geological time. To get there the bacteria had to develop photosynthesis and become cyanobacteria, blue-green algae. Then the oxygen they produced had to oxidise the reduced iron in the rocks. There’s a rust belt recording the epoch, literally.
Only once oxygen levels began to rise appreciably in the oceans did the drive for anaerobic cells to find some way of surviving which brought a large bacterium into engulfing a small oxygen capable bacteria and fail to digest it leading to a symbiosis at the basis of all animal, plant and fungal life.
The plants, necessary to make foodstuffs for yeast to work on required a second symbiosis between a eukaryotic cells and cyanobacteria where even today all the photosynthesis happens in plants.
Since barley and hops are both flowering plants you get well into the Triassic at least before you can make beer. But really it has to wait until the hunter gatherer humans selected larger ears of grass and let them ferment. Good for sourdough bread and beer both.