Believe it or not, but rice is actually more important than the fish that accompanies it. It seems quite simple, but it's something that can take forever to get the hang of.
Sushi vinegar is usually sour in flavor and slightly sweet. It's basically comprised of....
Kombu (dried kelp)
Of course you can find premade sushi vinegar in stores, but if you want to make your own here's a simple recipe.
1 part rice vinegar
1 part white sugar
1/2 part salt
1 piece of kombu about the size of your palm (if you don't have any, skip it)
Mix the first 3 ingredients together in a pot over a low heat then place the kombu in. You want to constantly stir this mix (still on low heat) so that the salt and sugar disolves.
When everything is well combined, remove it from the heat and let it cool.
If you want you can squeeze some lemon and orange juice into the vinegar for some extra flavor :)
The vinegar can be stored at room temperature and will last a while if you made too much. And besides being used for rice, it can make a great dressing. You can easily make a cucumber salad called "Sunumomo" ("su" means vinegar.) That's just made of thin sliced cucumber that's dressed with vinegar.
Anyways, the main use for this vinegar....
After you've cooked your white rice you should move it to a bowl that's not going to retain heat. You want the rice to be hot when you start out, but it's going to have to cool down after the vinegar is incorporated.
It's about 2-3 tablespoons of vinegar to 1 cup of cooked rice. Usually a chef always knows the amount per batch or will add till the right saturation level is reached (That's something that people learn over a period of time.)
Mix the rice and vinegar around using a sideways, slicing motion. You want to mix and separate the grains, but don't smash them. Durring this process you can fan the rice to speed cooling or let it sit and mix periodically to release the steam.
Now you're done!
Sushi rice can be kept for a couple of days. It can be left room temp if it's in a sealed container with a damp towel over the rice. Putting it in the fridge will cause the rice to harden. Also make sure not to store your rice until it has reached at least room temperature because placing hot sushi rice in a sealed container will cause discoloration.
Thanks, for reading :)