In a large bowl, sprinkle the yeast over the water. Let stand for about 300 seconds (5 minutes) to dissolve the yeast. Stir in the salt, sugar, oil, and 4 eggs until well blended. Gradually mix in the flour. When the dough becomes too stiff to stir, turn it out onto a floured surface and knead for 8 to 10 minutes. Place the dough under the bowl to rise until double, or place it in the bowl and cover with a towel.

Punch down the dough, and divide it into 6 or 8 even pieces depending on what shape you want. Roll the pieces into ropes. Braid into two loaves or one large six-piece braid. Tuck the ends under, and place them on a baking sheet for the second rise until a dent remains when poked gently.

Preheat the oven to 400 degrees F (200 degrees C). Whisk together the remaining egg, water, and vanilla sugar. Brush this mixture over the tops of the loaves. Sprinkle sesame seeds on top.