ive got some flavorings nearing the 1.5 year mark. so i popped a question over to TPA regardign their usability. below is the response. i feel like everyone can benefit from this info 
"Concentrated flavors do not spoil, or go rancid, like fruit juices can.
But under certain conditions they can change.
Basically, what my flavor manufacturer tells me is that the flavors have
a shelflife of at least six-months to one-year, when they are not
continuously opened. It is not necessary to store them in the
refrigerator, but I don't think that this would hurt them. But sometimes
refrigeration can cause re-crystallization of flavors that have a lot of
the crystals like ethyl maltol in them.
Here's some background.
Every concentrated flavor is a mixture of raw materials, and every
flavor blend can act differently. For example flavors that have a
vanilla characteristic are going to have slightly different storage
capabilities than fruit flavors. Here's the reason.
Vanilla and caramel flavors are mostly made of large molecules like
vanillin, ethyl vanillin , etc.
These molecules are not very volatile, and tend not to escape the bottle
when you open it. They will be fairly stable. Fruit flavors, on the
other hand, are made of much smaller molecules in general. Whenever you
open a bottle, it's the lightest and smallest molecules that escape and
reach your nose quickly. Over time when you open a bottle over and over
again more and more proportion of these lighter molecules leave the
bottle and eventually the character of the flavor will be changed. This
doesn't mean the flavors spoiled, it's just different. So this is one
piece of advice, if you are going to store a flavor for a long period of
time, transfer the flavor to smaller bottles that will you will not have
to open over and over again.
also, when a flavor is warm, like if it's a hot day, when you open the
bottle even more of the volatile molecules will escape, much more will
escape than if the flavor was cool. This is true for all liquids, when
liquids are heated the molecules are much more easily converted to their
gaseous state. So in general it is a good idea to keep the flavor cool
though I don't think refrigeration is always necessary.
Also, in general, it is best not to store these flavors long-term in
plastic.
The plastic that we ship our larger sizes in ( 4 ounces and above), is
HDPE plastic, which is very resistant to interaction with the flavors.
but even with HDPE plastic, I really wouldn't recommend storing them for
longer than a month or so.. It's much better to store things long-term
in glass.
also, it is not a good idea at all to store the flavors with the plastic
eyedropper caps on the bottles. The rubber that's used with the
eyedropper's is extremely soft and interacts with a great many
materials. If you try to store your flavors with these rubber dropper
caps attached you will most likely ruin both the caps and the flavors.
i hope this helps, linda"
enjoy
"Concentrated flavors do not spoil, or go rancid, like fruit juices can.
But under certain conditions they can change.
Basically, what my flavor manufacturer tells me is that the flavors have
a shelflife of at least six-months to one-year, when they are not
continuously opened. It is not necessary to store them in the
refrigerator, but I don't think that this would hurt them. But sometimes
refrigeration can cause re-crystallization of flavors that have a lot of
the crystals like ethyl maltol in them.
Here's some background.
Every concentrated flavor is a mixture of raw materials, and every
flavor blend can act differently. For example flavors that have a
vanilla characteristic are going to have slightly different storage
capabilities than fruit flavors. Here's the reason.
Vanilla and caramel flavors are mostly made of large molecules like
vanillin, ethyl vanillin , etc.
These molecules are not very volatile, and tend not to escape the bottle
when you open it. They will be fairly stable. Fruit flavors, on the
other hand, are made of much smaller molecules in general. Whenever you
open a bottle, it's the lightest and smallest molecules that escape and
reach your nose quickly. Over time when you open a bottle over and over
again more and more proportion of these lighter molecules leave the
bottle and eventually the character of the flavor will be changed. This
doesn't mean the flavors spoiled, it's just different. So this is one
piece of advice, if you are going to store a flavor for a long period of
time, transfer the flavor to smaller bottles that will you will not have
to open over and over again.
also, when a flavor is warm, like if it's a hot day, when you open the
bottle even more of the volatile molecules will escape, much more will
escape than if the flavor was cool. This is true for all liquids, when
liquids are heated the molecules are much more easily converted to their
gaseous state. So in general it is a good idea to keep the flavor cool
though I don't think refrigeration is always necessary.
Also, in general, it is best not to store these flavors long-term in
plastic.
The plastic that we ship our larger sizes in ( 4 ounces and above), is
HDPE plastic, which is very resistant to interaction with the flavors.
but even with HDPE plastic, I really wouldn't recommend storing them for
longer than a month or so.. It's much better to store things long-term
in glass.
also, it is not a good idea at all to store the flavors with the plastic
eyedropper caps on the bottles. The rubber that's used with the
eyedropper's is extremely soft and interacts with a great many
materials. If you try to store your flavors with these rubber dropper
caps attached you will most likely ruin both the caps and the flavors.
i hope this helps, linda"
enjoy
