http://www.durgan.org/URL/?VPOSM 27 July 2012 Potato Juice
Experimenting with the garden produce with the intention of processing for use off season, it was decided to make juice from potatoes. Traditionally, potatoes are stored in a root cellar and used as required. Needless to say they deteriorate considerably over time. My view is why not process while they are pristine, hopefully obtaining most of the nutrients.
My method; Three pound of potatoes freshly dug were cut into pieces and hand blended into a slurry. A total of three litres of water was added to make the end product thin enough to drink. The slurry was cooked in a double boiler for about half an hour.This prevents burning. The cooking causes the potatoes to thicken considerably. This was when the water was added to thin. The cooked potatoes were then poured into litre jars and pressure cooked at 15 PSI for 15 minutes.Even by adding almost three litres of water there was only three litres of juice. Experience has indicated that it is not good practice to attempt pressure canning very dense materials. The reason is it is problematic that the contents of the jars reach 250F, which is the desired canning temperate, which kills all bacteria.
The experiment was a disaster. The potatoes turned into paste and were sort of slimy. Clearly this is not a method to preserve potatoes.