Natural cacao powder is pulverized untreated cacao solids. Once the nibs are ground and pressed, the remaining defatted solids are milled into a fine powder. It is lighter in color and is lower in pH (between 5 and 6). Due to the powder being left in its natural state, it has the stereotypical bitter taste that is associated with cacao. If this is used as an ingredient in baking, usually baking soda is required to balance the pH of the food.
On the other hand, there is alkalized cacao powder (sometimes known as Dutched or European-style cacao powder).
 
It was first made in the 19th century by a Dutch chocolate maker called Coenraad Johannes van Houten. It is treated with 2% potassium carbonate (a salt), which neutralizes the cacao’s acidity to a pH closer to 7 (the same pH as water which is considered neutral). The more alkali and more reaction time, the darker the powder, that has a softer taste.