It is a lie to say that natural penicillin is highly unstable or filled with deadly impurities. It is true however that Fleming's original strain of penicillium yielded so little penicillin that the resulting un-concentrated penicillin filtrate was too weak to cure a patient when given by IV, without literally 'watering' the patient to death in the process.
Unfortunately, penicillin was relatively unstable, so that any amount of heavy concentrating of it, to a point where IV injections became life-savers, usually destroyed most of the penicillin in the process.
The chemists had a modern city-boy solution - a terrible synthetic solution - that killed far more life-saving penicillin than it yielded.
The best solution, in fact, was to greatly up the yield of penicillin per penicillium plant , just like any old fashioned farmer would have done with their milk cows.
Thousands of years old (or new), breeding still works its simple magic to this day.
When a few people actually went the farmers' route instead of the chemists route, the crisis in wartime penicillin was over - forever.
Using a few bits of low tech equipment that you could find in any hardware store, like $10 UV sun lamps , they soon upped the yield by 500 times.
Since then it has been upped further by an amazing 50 to 100 times more.
Profits can still be made in penicillin making but the smart guys in those Indian companies doing so, don't rely on patents.
The complicated chemistry techniques down stream from the actual creation of raw natural penicillin is all pretty well known and in the public domain.
But the profit centre deep inside those factories is a trade secret , or as farmers would say, my prize bull, and mine and mine alone .
This prize bull of a penicillium spore, chews a bit of cheap trashy junk sugar and then squirts out more squirts of the joy-juice than Ron Jeremy has had hot dinners.
The downstream chemical work might not be of the Harvard University grade but who cares, the prize bull has delivered so much goods, that the chemists can afford to spoil a little .....