In the back of the kitchen, we had a ketchup refill area which used a large bag-in-box system; here is what that looks like: https://i.imgur.com/jP8zrrI.png

As you can imagine, the bag lasted quite a while as we would just top up the classic red ketchup bottle with a screw lid. But...because our restaurant (Hamburger Mary's) was low/no-volume from Monday to Thursday, those bottles just...uh...sat on the tables for days on end, at most they'd sit out for a week.

On the tables.

At room temperature.

With constant exposure to air.

You can probably see where this is going:

The ketchup would gradually ferment due to the warm room temperature and continuous exposure to air. This fermentation process gave it a unique ‘tangy’ flavor that some customers mistook for a special “beer ketchup”. Given that I worked in Milwaukee, WI (a city known for its breweries and beer culture) their assumption wasn’t entirely baseless

But in reality, they were complimenting the taste of…well…rancid ketchup.

I left shortly after that experience to a real restaurant (Rock Bottom; if you like cajun pasta, here is their recipe for it: https://imgur.com/a/fjZnDAz) but yeah -- definitely be careful where you go to eat. Higher than normal employee turnover is absolutely a warning sign that the restaurant is poorly run and probably not the best place to eat.