[Scotford]

Ooh ooh ooh. Try The Force!

 

[Scotford]

A mangle could work too

 

[Scotford]

Personally, I'd advocate putting the entire bag in a trash compactor.

 

[Scotford]

Now you're into my kinda bodge job territory.

In the past I've used:

A pestle and mortar (very hard work)

A salt grinder (also very VERY tiring)

A rolling pin and two tea towels (not so much hard work, more tedious)

A porlex with no handle using a set of pliars (tedium)

A rhino with no handle using pliars (again, tedium).

I'd take them to your local shop and get them ground. If its a decent independent, take them out of the Starbucks packaging though.