Unusual? See, it's hard to make a case that anything is "unusual" online anymore.
I had to sit and think about it for a few minutes.
There is an interest that I have only personally known of two people to have, outside of people who work in the industry. Where particular foods and beverages are manufactured. Both of the people I know who are interested in this are on the autism spectrum and are very particular about what they eat. I'll give an example about my husband, who is one of these two people.
Apparently, Red Bull is manufactured in a few different places in the world. Most of us can't tell the difference between the drinks and where they are made. But my husband says it tastes better when it is in the 8 oz cans with certain markings on them and also the 20 oz cans. Those are both made in the same facility.
There was a Pringles manufacturing plant fire many years ago that changed the taste of Pringles, according to my husband. He has not liked them since then. He says they do not taste the same.
So that is an unusual interest. Food manufacturing.