First, a surprising case for manual labour:
Assuming that the right type of bottle has been decided upon and purchased, the next step is to ensure its cleanliness and sterility before it is filled. This precaution would at first sight appear to be a simple matter, but experience has shown that such is not the case. It has lately been found necessary to install intricate, and, in some instances, very heavy machinery to do the work of bottle washing. Wonderful machines have been designed to take the place of manual labour, but one has not been invented which can smell the dirty bottles, and reject those which have been wrongly used for holding paraffin, oil or disinfectants.”
Brewing Theory and Practice" by E. J. Jeffery, 1956, page 349.
I doubt this is much of a problem nowadays, even in countries which still have returnable bottles. I can’t imagine anyone needing to use a beer bottle to hold those sorts of liquids. I guess with screw-stoppered bottles re-use was more likely. If you’re using all new bottles, as is the case in many countries now, then this situation can’t arise.
Judging by the amount of text Jeffery devotes to the topic, contaminated bottles was a big problem back in the 1950’s:
“Mentioning contaminated bottles compels us to state that this bugbear is the greatest problem which besets all bottlers, in spite of all precautions. Wrongly used bottles are almost impossible to put right, and people who so maltreat them should be held responsible and made to pay for them. Unfortunately it would be difficult or impossible to enforce such a step. The only solution therefore appears to be frequent notification by placards and leaflets of the financial loss and danger occasioned by such ill-usage. All empty bottles must be carefully examined on return, both by the licensed retailer and by the bottler. In spite of the rigid enforcement of this inspection, and in spite of a bonus being given for the detection of contaminated bottles, some still find their way occasionally into the bottle soaking tank. Should this unfortunately occur, there may be no alternative but to empty the tank and search for the offending bottle. If contamination has been severe, it may be found necessary to give the bottles an extra soaking in hot caustic soda solution. This solution should be run away and replaced by the normal solution. The only safe way to deal with the bottles used for the improper purposes described is to break them up. It would seem to be impossible for a hard substance like glass to retain any flavour, yet it often does so.”
"Brewing Theory and Practice" by E. J. Jeffery, 1956, pages 349 - 350.
Presumably the notices said that the deposit would not be returned on contaminated bottles. A dirty bottle leaking something like paraffin into the soaking tank must have been a nightmare. It sounds like it was messy and difficult to correct. I bet it drove the bottlers crazy.
We’ll be looking at the machines themselves next.