I've kept 30 gallons of lme for longer than 6 months. Just suck all the air ( oxygen ) out with a vacuum pump and it will keep for a long period of time if refrigerated.
You might want to look at buying DME in bulk (50 lbs at a time). It does not have the problems associated with DME (darkening and metallic taste from the can).
LME doesn't store particularly well. It will darken over time and produce extract twang. If you buy LME in bulk, make sure you use it all in several months' time. It is very important to keep it refrigerated.
I like the flavor of LME better, but if I were going to buy extract in bulk I'd get DME. It will last much longer as long as you keep it in a dry place.
I've been using Cooper's LME's,since their cans have that white liner in them. No metallic taste from it. I got a midwest cascade pale ale kit (PM) with a small "milk" jug of plain gold LME with it. It's sealed up in the fridge for about a month now. One more week or so till my new stove burners come in. Then it's game on & I'll report back with results. Even the grains look to be keeping well in the fridge,sealed in there bag with a zip tie.
I checked with Northern Brewer - theirs comes in what looks like milk jugs. I was told they don't recommend putting it in the refregerator. Said it could even be detrimental because it can cause moisture pockets and mold. I haven't tested this, so I can't really offer an opinion.
I've always refridgerated mine,& as long as it's still sealed,it stays fresh & no problems. Mold needs air & warmth to propagate. As long as no air gets in the container & fridge is cold,I never saw it happen.
I wonder if the milk jug packaging Northern Brewer uses could make a difference - maybe some air space causing a problem. I don't have any here now, or I'd look and see.
The lil jug I got from midwest has no air space,so if yours dosen't,I wouldn't worry to much about it. Sealed in the fridge doesn't make for a good breeding ground for mold. Just things that are unsealed will molder eventually.