I have tried making buns and pizza muffins using all purpose flour (bleached/unbleached/bread flour are not available in my country)multiple times at 180-200C in the middle rack of my oven. They never brown from top. I have tried applying butter on top and even doing a milk wash.please suggest what to do?
Egg wash is an answer.
[For a shiny crust, brush the top of the bread with an equal solution of whole egg, water and milk. If desired, sprinkle with poppy, caraway or sesame seed or rolled oats. For a softer, deep golden brown crust, brush with softened butter or margarine. For a crisp crust, brush or spray lightly with water. For a soft, tender crust, brush with milk. After glazing (brushing with one of these ingredients), slash the top of the loaf with a sharp serrated knife, cutting about 1/4 inch deep, once down the center of the loaf or across the loaf a few times.]
There are two ways in which bread gets browned:
Maillard reaction between amino acids and reducing sugars,
Caramelization of sugars.
Both are forms of non-enzymatic browning.
Maillard reaction. You can promote the Maillard reaction by using stronger flour (more proteins, so more amino acids). Disaccharides such as table sugar (sucrose) are not reducing, but are broken down into reducing sugars (glucose and fructose) by the action of yeast. So you need to make sure that your yeast is active and give it plenty of time to work.
A milk wash or, better still, an egg wash (only the white is needed) will add proteins directly to the surface of the bread.
Caramelization. Just add sugar. I find even a teaspoon of table sugar gives a noticeably browner crust in my bread. (But, thinking about it again, this could be because it gives the yeast something to turn into reducing sugars.)
Generally. A higher temperature or longer baking will also help.