I just thru about 10 bags out a month or so ago as they were about 7-10 years old.

It was just getting aged. 

If you reseal the package tightly without any air, it will extend the its usability. I lightly vacuum pack mine after each use, clumping has not been a problem since I started this method.

Yes!  Air is the culprit.  If you look on your grocers' shelves, you'll see that companies package their brown sugar in air-tight bags.  It's fine sitting unopened for months.

To keep brown sugar at the same freshness level we need to keep it at the same air-tight level.

Bump!

There's a solution that's better than vacuum sealing.  Do an Internet search for Brown Sugar Bear.

It's made of clay.  You soak in in water, wipe it dry and put it in the brown sugar container.  It keeps the brown sugar from drying and clumping.  You can even put it in with a brown sugar brick and it will restore the sugar's required moisture.  You'll need to re-wet it if the sugar begins to form hard "clumps".

(I always thought that the exposure to air caused humidity to "clump" the brown sugar.  Not so—it's obviously the lack of moisture.)

I think my wife has been doing that for years.

I have seen those clay discs. About the size of a silver dollar if I recall. I usually buy dark brown sugar at the Amish store. They must get it in bulks and package it plastic bags with twisties to secure. It rarely dries out until the bag is almost empty and you can no longer twist the bag tightly. at that point I put a few drops of water on it and toss in the microwave for a few second on a lower power. I think the dark brown having more molasses in it probably keeps it from drying out at fast as the light brown.

I picked up these at The Container Store.  Made for brown sugar.
They have the clay puck on top that you can remove and soak in water for a half hour.

I still have several bags also that are 6-7 years old. I'm not sure if sugar has a shelf life, there is no "use by" date on my packages.

I still have several bags also that are 6-7 years old. I'm not sure if sugar has a shelf life, there is no "use by" date on my packages.

 Turns out, sugar takes the cake when it comes to extended shelf life. Granulated sugar can last up to two years in the pantry after opening. Technically, sugar never spoils. While it's recommended that granulated sugar be discarded after two years, chances are it will still serve its baking purpose even beyond that.Dec 24, 2021

This is super interesting. I've used the oven method before (spread out on a cookie sheet and heat at low temp). Never heard of the clay method, that's very neat!

Put some in the microwave for about 60 seconds tonight, worked well.  I have also put freshly peeled orange rind in it, but that only last for about 3 weeks.