@sejintenej
The penicillin we use was developed from a mould on a canteloup melon but had to be treated further
Penicillin chemistry was an area of my undergraduate research.
Correct. The original organism was Penicillium notatum, but the strain you mention was Penicillium chrysogenum. Key difference: P. notatum is strictly aerobic so only can grow on the surface of the culture medium, while P. chrysogenum can be grown in an aerated liquid. Even before growth accelerators, productivity of the latter is based on the cubic volume of culture medium, not the square surface.
I doubt that you'd get a useful concentration from bread mold. Now, I'm going ro rely on memory here, for an extraction that I haven't done in a few decades. One filters off the mycelium (the visible mold), then acidifies the liquid, and shakes it (or uses more efficient mixing) with petroleum ether. The crude penicillin leaves water solution and goes into the pet. ether. Additional steps involve successive solvents that are more preferred by the penicillins, reducing the volume and eventually evaporating.
During WWII, when the first clinical use was done, everything was in short supply. They needed flat large-volume culture media that could be sterilized. A creative supply person came up with a large stock of covered porcelain bedpans.
The first patient was a member of the Oxford police force. They really didn't have enough to treat, but he was clearly dying. His response to the first doses was miraculous. They tried their best to extract enough excreted penicillin from his urine, but ran out, and sadly watched him die.
This led to the jingle,
"Penicillin. A most strange substance.
Grown in bedpans
And purified by passage through the Oxford Police Force."
I've thought about if I could make it, or other drugs, in a time travel story. My answer is maybe, depending on what chemicals and equipment were available. I'd try some extraction techniques that might be more efficient, such as absorption onto activated charcoal. Column chromatography might be an approach to later stages.