How do you prevent your solder paste drying out?

[Cain]

Quite a few times it dry's out for me in the syringe (in the needle). To counter that I just started pushing a thin needle into the syringe (fits perfectly) and then place a blob of "clay" (don't know the English term for it but if I say it's used to put up posters on the wall you know what I mean ) to make it air tight.

Don't know it it works yet and curious how you guys are doing it?

[Checksum8]

I never had much luck with the syringes after couple of uses. So what I do now is spoon some out of the storage syringe and onto a plastic surface. Then I take some "Chipquick" SMD291 flux and mix it in a little at a time until I get the right consistency. Then I put this into a clean syringe. Or stencil it on. The flux brings the solder back to life. I wouldn't use this method on a production run or some critical application. But for protos and hobby use it seems to be okay.

[Gallymimu]

I use the tapered luer lock style http://www.newark.com/productimages/standard/en_US/3757518.jpg

I keep it in the fridge, in a ziplock, and generally don't have any problems.  We have some syringes that have been in the fridge for a year with use ever few months and it is generally OK.

[vern]

Put it in a Ziplock in a fridge. Smoothe out as much air from the ziplock as possible before closing it.
If you have some desiccant bag from buying components put them in the ziplock too. With moisture the solder paste will age faster.
Before using let it warm up to room temperature in the ziplock, because otherwise humidity from the air will condense on the cold paste and spoil your solder joints.

[snowman666]

I sometimes add a bit of isopropyl alcohol to the solder paste when the texture becomes too thick and hard to work with. I then mix the stuff and store in a fridge. The alcohol helps improve the viscosity and long term storage. The best part of this, is that the alcohol evaporates during the reflow process 

[optikon]

I keep it in the fridge, in a ziplock, and generally don't have any problems.  We have some syringes that have been in the fridge for a year with use ever few months and it is generally OK.

This works for me too. I use only the jar containers of it, gave up on the syringes years ago.

[kayvee]

I only use it in 500g jars/tubs, I don't have a problem, mainly due to I use them up too quickly before it has a chance to dry out

Keeping airtight and in a fridge is a must, and never open the before it has reached room temperature, as vern pointed out.

[pushycat]

Rather you cant directly prevent the solder paste from drying out but i tried a wired way which worked to be the best of all. Please note i am referring to the one flux which is yellow in color and  whose base content is Natural rosin. When the flux dries out, you can mix it with No clean white liquid flux which regains the soft texture of the soldering paste as well takes a long time to dry again depending on the quantity you add. It worked for me to preserve flux pastes. Or in case you know a bit of chemical engineering and know better of chemicals, you can formulate your own fluxes for immediate use and prefer not to store.
Flux formulas with their chemical compositions and lot information can be found on this link below which i found useful.
http://www.rosin-depot.com/liquidfluxformulas.html