When trying to bake white bread, I use yeast to make it rise. The problem is that I always get a sour yeast taste with my bread.
How do I avoid this "sour bread" effect?
I agree with martierts answer in that you might have been using too much yeast. If you'd like to reduce the amount of yeast but are afraid of your bread not rising enough, make a sponge. My experience is that the bread will still rise just as well, but not taste of yeast that much.
Take a quarter of the yeast you're using now, half the flour and three quarters of the liquid of the recipe, mix well and let it sit for twelve hours in a covered bowl (do not add any salt at this stage). After that time, add the rest of the flour and liquid and other ingredients and another quarter of the original amount of yeast.
I've been making bread rolls for two years now, and by making a sponge this way I have reduced the amount of yeast by half, and for me it greatly improved the taste of the end product.
Try a different yeast
Any beer brewer will tell you that the yeast you use can make up to 50% of the flavor of the beer. Different yeasts produce different flavors. The same is true for bread.
Now, if you're getting a "sour" effect, it's possible that you have bacteria hanging out with your yeast. (A sour dough culture is a mixture of bacteria and yeast that co-exist. The bacteria are frequently responsible for the "sour" taste -- which I happen to like...)
Try keeping your work area, hands, and bowls sterile
Perhaps you're infecting your dough when you're kneading it. Wash and/or sterilize everything that comes in contact with the dough. When you waiting for it to rise, cover it with plastic wrap to keep anything from floating thru the air and landing on it.
(Beer brewers tend to be obsessed with cleanliness for this same reason. Don't want random bacteria infecting the beer.)
I like Fleischmann's RapidRise or BreadMachine yeast, mostly because it shortens the rise time and you don't need to rehydrate the yeast (create a starter) like traditional yeast.
Also, I read on another website that the sour taste can come from using too much salt and/or using old yeast.
Another thing to consider: maybe the yeast taste isn't bad, just something you aren't quite used to yet. I like to get a little bit of that yeasty flavor. Might be something that grows on you. (No pun intended.)
It might be because you use to much yeast. You can experiment on how much yeast you actually need in your bread. Start by using half. If it's too little, use the amount you used + 50%. Repeat until you have found the perfect amount of yeast. If it's too much yeast, you should no longer taste it.
EDIT: Could also be because you let it raise to long.