Ok, let me get this straight, you have gastritis and you want to drink potato juice? Are you nuts? Potato juice is the last thing that you should be drinking. Please avoid it all costs. If you stomach has gas problems then you will compound it even further with potato juice. Avoid anything that can cause gas or gas related trouble in your stomach. Stick to raw vegetables and fruit juices and avoid packaged products as well. Alcohol is also strictly prohibited during this period. You can eat plenty of curd and fruits like musk melon and water melon. Cheers!