Sources: Food Republic, the Pioneer Woman
For standard simple syrup: Use one part sugar to one part water, by volume (e.g. one cup sugar, one cup water)
For "rich" simple syrup: Use two parts sugar to one part water, by volume (e.g. one cup sugar, 1/2 cup water)
Combine sugar and water in a small saucepan over medium heat. Heat until the sugar dissolves, stirring. Once all the sugar has dissolved, remove from heat.
Possible flavorings include: herbs (rosemary, thyme, mint, basil); citrus peel (orange, grapefruit, lime); spices (vanilla beans, cinnamon sticks, cloves, nutmeg, ginger, peppercorns, cardamom, fresh or dried chiles).
Once the simple syrup is cool, remove the additional ingredients to prevent spoilage.
Store the simple syrup in an airtight container in the refrigerator. Storage times are:
Standard simple syrup: up to a month
Rich simple syrup: up to 6 months
Flavored simply syrup: two weeks
Keep in mind that the sugar dissolves into the water, so 1 cup of sugar and 1 cup of water does not equal 2 cups of simple syrup. It’s more like 1 1/4 - 1 1/2 cups. Adjust your measurements as needed.