Fermented tofu will not keep indefinitely but has a significant shelf-life of between six months to a year. The fermentation process continues, even if refrigerated, and it will reach a point beyond which it will be inedible. This expiration date is often determined by the type of ferment, as some ferments can take six months just to reach maturity.
You can ferment sauerkraut too long, at which point it will become mushy, and the taste will be too acidic, even though the sauerkraut will still be edible. Longer ferments will intensify the flavors and tangy taste of the sauerkraut. The length of your ferment is usually according to your personal taste. The traditional ferment for sauerkraut is about four weeks, but some people prefer a 3-day ferment.
When things rot, the bacteria that cause decay proliferate on the item and begin to break it down. Fermentation is the introduction of good bacteria that inhibit the growth of the bacteria that cause decay. This has the effect of preserving the food item for longer, and even enhancing its nutritional value due to the presence of the good bacteria!
It is definitely possible to survive on rice and beans alone, since the meal is considered to be a complete protein, providing all 9 amino acids that are essential to life. The carbohydrate value of rice provides a good source of energy. Rice and beans partnered together will make a survival food that can sustain you indefinitely if you can stand the boredom!