Garlic powder doesn't taste like garlic because the garlic powder goes through a drying and grinding process which alters the chemical compounds that are responsible for the garlic's distinct flavor which is most particularly the allicin in garlic.
Fresh garlic contains allicin which is a sulfur compound that gives the garlic it's pungent and sharp flavor and aroma.
However when the garlic is dried and powdered the allicin gets partially broken down or inactivated and results in a less intense and different flavor profile.
The best substitute for fresh garlic is frozen garlic cubes.
Frozen garlic cubes are the best substitute for fresh garlic because they are made from fresh garlic which is processed and then flash frozen quickly to preserve the bright and vibrant flavor.
Granulated garlic or garlic powder can also be used as a substitute for fresh garlic although it doesn't taste as good as fresh garlic or frozen garlic cubes.
When substituting granulated garlic for fresh garlic use 1/4 of a teaspoon of the granulated garlic in place of each garlic clove.
For garlic powder use 1/8 teaspoon of garlic powder in place of each garlic clove.
Not all garlic powder brands are the exact same.
While all garlic powder is made with real garlic cloves that have been dehydrated and ground into powder they are not all the same.
Different brands of garlic powders have different variations in ingredients, texture, flavor profile and quality.
Some brands of garlic powder use higher quality garlic, organic garlic or even specific varieties of garlic which can impact how the flavor turns out and also impact the nutritional profile.
Different brands of garlic powder also can be processed differently and the way the garlic is dried, ground and process can also affect the final flavor, color and texture of the garlic powder.
And some brands of garlic powder also add anti caking agents, fillers or other ingredients to the garlic powder which can also affect how the garlic powder taste and the quality.
Garlic powder can also range from a coarser, granulated texture to a fine powder which can also impact how the garlic powder is used in cooking.
Some garlic powder brands may also have a more pungent and stronger flavor and other brands of garlic powder may be milder or have a slightly different taste as a result of the garlic variety or the method of processing the garlic powder.
The color of the garlic powder in different brands can also vary from deep grayish-purple to pale white depending on the variety of garlic and method of processing.
And some brands of garlic powder also dissolve better in oils or liquids than other brands which is important in some cooking applications and recipes.