http://www.youtube.com/watch?v=cuPdf3bFqZE
It makes sense to understand how freeze dried coffee was invented at all.
For a long time spray dried coffee was used. After world war II there was a technology invented to dehydrate medical fluids like serum, liquid antidotes etc. It was a necessity as there was no efficient cold chain to transport things like these across the globe. This technology was based on the concept of sublimation.
After the war the technology was put out for peace time uses. This was when coffee picked it up for use and Lo! we have freeze dried coffee
This reduces weight and makes it easy for transport at the same time being superior to the spary dried coffee used till then