What is prison food like?

The best way to describe it is to say microwave food. It’s the crappy food that you wouldn’t feed your children every single day.

Let me give an example:
Friday’s is fish, no matter what. And it’s always the same kind of fish. A fillet. It’s real fish though, and it’s not completely awful, until you eat it every single Friday for so long. The thought of fish fillet hurts my stomach now.
Now, in CCWF there was a central kitchen where they would cook real food. Unfortunately it burned down and has been supposed to reopen for like a year and a half already. I hope it’s open by now. Everyone said that food was better and there were larger portions. They said there was big huge pieces of cake.
It sounded a lot better than what they were feeding us. I gained a lot of weight eating tritaters. Which are basically giant tater tots.
Juliana Linn, had an extended stay in CCWF

In county jail (and from what it sounds like on the other answers, San Quentin too) the food looks exactly like this.
Beans beans beans, and then some more beans. Maybe some weird rubber meat mixed in for variety.

The quality of the food appears to be the lowest quality available. More often than not, the meat is best described as “mystery meat.” For vegetarians it is a constant flow of peanut butter, cheese, boiled eggs, and beans. But the distastefulness of the food has more to do with the unsanitary conditions in which we are often forced to eat (e.g. birds flying around in the chow hall, usually pigeons, with droppings on the tables or falling from the overhead steel railing on which the birds perch themselves) and preparation (unclean food trays and overcooked or undercooked entrees).

Larry Histon, inmate San Quentin State Prison

Prison food is the opposite of my mothers cooking. There is no smell and the food taste bland. One thing for sure when I do get out of here, no beans for me. Sometimes we are fed beans for breakfast and beans for dinner. The only thing is the beans are dry and sometimes hard. I like beans not rocks for breakfast or dinner. Now the eggs are always cold and be careful because there might be a piece of egg shell laying around. Fresh bread doesn’t make its way to prison. The bread isn’t soft but it’s not hard, sometimes the end piece is on the tray as an extra. The hottest item on the breakfast tray is the hot cereal. Either corn meal mush or crack wheat oatmeal. Sometimes the butter will melt, that’s when the butter can be spread on the bread. Prison food is horrible as it should be. Prison food is not meant to get a prisoner full, just enough to maintain survival.

Dinner is the worst, most of the time some kind of chicken goulash is served in the chow hall. What is prison goulash? Close your eyes and imagine you are in a bean factory, with a vegetable garden and you put everything including the dirt in a big pot. Serve all that over brown rice that’s half cooked or over cooked with a hard biscuit and unsweetened jelly for dessert. That’s prison goulash grade A dinner and it might be hot. Most of the meat, soy bean mixed with a small amount of real beef. You can’t tell if the beef was once living or out of a lab. The beef doesn’t have a smell. Now I am from Houston Texas land of the beef cattle and I can tell you this much. That ain’t beef! Prison food is like playing Russian roulette, you never know what you’re eating.

Joseph Demerson, Inmate San Quentin Sate Prison