Flavor Expiration and Storage
Flavor concentrates will not go bad; at least not in the sense that they shouldn't be used. They can, however, change over time. In fact, this is why steeping is such an important part of any good recipe. These changes depend heavily on the flavor in question and the environment they are exposed to.
Oxygen and light are the leading factors in flavor transformation, and can cause minimal or significant changes depending on the flavor. Flavors comprised of larger molecules such as vanilla are not as volatile as flavors made up of smaller molecules, such as fruit flavors, which can be very volatile.
Smaller molecules are also more likely to escape when the flavor bottle is opened, especially in warmer conditions when the molecules are more energetic. Larger molecules tend to stay put, and do not escape as easily when exposed to air.
These processes do not spoil or necessarily degrade the flavor, but they can cause subtle changes in its character. For example, if a flavor has a high alcohol content, portions of the alcohol will likely evaporate when opened. This can tone down the bitter taste of alcohol, which can actually have a desirable effect on the character of the flavor.
Since flavor concentrates do not spoil, they often include “Best By” dates instead of expiration dates. These dates vary, but typically range from 8 to 24 months. These dates are not set in stone, and most of the time flavors will still taste great far beyond the listed date.
Flavors are best stored in a slightly cooler than room temperature environment, with minimal exposure to light. Refrigeration is not necessary.
Ideally, you want to open your flavors as little as possible, minimizing their exposure to oxygen & light. Purchasing multiple quantities in smaller sizes may better suit you needs depending on your setup and use.