According to the UAL forum, the fluid was water.

As far as coffee goes, a certain Canadian Turboprop can handle a large Dunkin Donuts with cream and sugar and it will not affect its flying abilities what so ever. Sure you'll lose the channeling ability on the number one com, but you can use the FREQ page on the KNS to select a different freq.

And you may see numerous flags on the ADI and HSI as the AHARS units have coffee spasms due to the selector panel being inundated. And there may or may not be some issues with the ADF selector panel, and there may be some weird odors as the sugar and cream cook off......