How do you keep dehydrated broth (powder) from clumping?

The clumping is a result of air and moisture entering the container with the substance. This especially happens if you pour the mix directly from the container over a hot dish - the steam enters and immediately clumps the spices. What you can do is to transfer your mix into a new dry and airtight container. Hope this helps :)

To break the clumps up, just use physical force.

Put the stuff in a sealed, heavy-duty plastic bag and whack on it with a rolling pin or a heavy bottle until it is in smaller lumps, then use your hands to break them down into the original powder.

As Adeline says, this is as a result of moisture (most likely steam) getting into the dry ingredients!

There is nothing wrong with the powder, if I were you I'd just crumble it into your food/gravy jug as and when you need it.

In future (to answer the question in the title) there are a few things you can do to avoid this happening:

• Store in an airtight container
• Ensure you open said container away from running water and hot food and for as little time as possible
• Add something to the container to absorb excess moisture. Rice is traditionally used in salt shakers, but it's probably a bit small for stock powder so I'd suggest dried beans.

(FYI stock = broth and by gravy I mean the British kind)

I would not recommend using the silicon gel pads as someone else has unless they are certified as safe with food. Most contain toxic chemicals that may leach into the powder over time.

THE PROBLEM IS NOT BEING TOO MOIST, IT'S TOO DRY !! Easy to fix & no need to resort to hammers, dissolving in water & freezing cubes etc.
To prove this I took 2 chunks of hardened stock powder (broken up & prised out of the container with a knife). One chunk I put in the oven for a few minutes to dry out - it went harder than ever & was difficult to break up. The other chunk I did what I would do for rock hard brown sugar & put it in a dish, covered with moist paper towel & a lid, then microwaved for 10-15 second intervals & stirred with a spoon in between - it soon softened up & returned to a flowing mixture. Yay !!
If you don't have a microwave or can't get the hard powder out of one of those cardboard & metal containers (that shouldn't be microwaved anyway) then try the following method (I know it works for brown sugar) Cover the container with a damp cloth & a lid & leave several hours or overnight, stir with a spoon & repeat if necessary - it will take longer but it should gradually soften up & be usable again.

Easy fix. In a dry climate, uncap jar for a few days. Then use handle of teaspoon to unclump. If that didn't work, my next step was going to uncap and place in slightly warm oven first; then use spoon handle.

My stock is in a plastic shaker but had gone all hard. I just softened it and dissolved it with a little bit of hot water in the microwave, it went to a smooth liquid. I poured this liquid into about an ice cube tray and now have 8 lovely cubes to use when needed! Yum.