Mix the yeast, sugar, salt, and water, and set aside for 5 minutes to activate the yeast.
Add the flour and mix well.
Cover and let it rise for 1-2 hours.
In a large saucepan, heat at least 3 inches of vegetable oil (7-8cm) on low. Too little oil will result in flatter balls.
Test to make sure the oil is hot enough by putting a drop of batter into the oil. If it is not hot enough, the batter stays at the bottom rather than rising to the top.
When the oil is hot enough, grab bits of the mixture with your hands or use a spoon to get small balls of dough and drop them carefully into the oil.
Fry for a few minutes until the bottom side is golden brown. Turn the balls over and fry for a few more minutes until the other side is golden brown.
Use a large spoon or strainer to remove them from the oil. I usually place them on napkins immediately to soak up the excess oil.
If desired, you can roll the finished product in cinnamon or powdered sugar to make it sweeter.