A new study suggests that alleged reduced food portions that have resulted from cost-cutting to the US prison system, have prompted inmates to start using ramen noodles as a form of currency. But this isn't the first time that food has been used as a form of currency.
Throughout human history there have been various food items that have also been used as a medium of exchange, including cinnamon, salt, parmigiano cheese, cocoa beans, tea, beer, and more. In UK prisons it's also reported that fruits are being used as currency with inmates, due to the lack of quality food that is served to them by the prison system.
When prisoners want to buy extra food they have the option of going to the prison commissary and they can spend whatever funds they have earned via their prison work wages or that was given to them from friends or family on the outside. Ramen noodles is being used as a currency because inmates see that it offers various benefits; the product doesn't expire for a long time, they are easy to exchange, and they are a convenient form of currency.
Right now the ramen soups, which can quite often be purchased for less than $.50 each, have become so valuable that they can reportedly be exchanged for a sweatshirt that is worth roughly $10.81. But the study was only examining one prison for the case study.
See:
https://www.cryptocoinsnews.com/12-types-currency-throughout-history-eat-drink-smoke/
http://www.news.com.au/lifestyle/real-life/fruit-becomes-an-alternative-currency-in-uks-youth-prisons/story-e6frflri-1225997797076
http://qz.com/763450/ramen-used-as-currency-in-prisons/