• Extend the shelf-life: After the syrup has cooled, stir in 1 ounce of vodka. This addition will help inhibit the growth of bacteria or mold, providing an additional 2 to 4 weeks of shelf-life.
• Heating the syrup over the stove is not necessary. Instead, you can use very warm water from the tap to dissolve the sugar. Although it may take a little longer for the sugar crystals to dissolve, this method produces a more fluid syrup that is less thick.
• How to know when the syrup has gone bad? If the simple syrup appears cloudy or has visible mold growth, it is a sign that it has gone bad and should be discarded.
• Add more to your coffee bar! If you plan on adding this hazelnut syrup to your coffee bar you might also want to try Brown Sugar Syrup, Rosemary Simple Syrup, or even Strawberry Simple Syrup to make a Strawberry Latte.

Variations

• Make a thicker syrup: The basic recipe for hazelnut syrup calls for a 1:1 ratio of sugar and water. If you prefer sweeter syrup, you can increase the amount of sugar, which will also extend its shelf-life since sugar is a natural preservative. However, this will also make the syrup thicker. Conversely, if you prefer a less sweet syrup, you can decrease the amount of sugar and increase the amount of water.
• Infuse the syrup with spices: Create an infused syrup by adding spices, making it an excellent gift for foodies or mixologists. Mix cinnamon, vanilla, or nutmeg into the simple syrup and allow the mixture to heat for 10 to 15 minutes to fully infuse the flavors.
• Use real hazelnuts: Swap the hazelnut extract for 1 cup of chopped hazelnuts. You'll need to cook the mixture for a minimum of 10 minutes and then let it sit to cool for about 20 minutes. Next strain the syrup through a mesh sieve. Discard the remaining hazelnut pieces.