I am creating a world where the currency (the only currency) is tablets that dissolve in water to create food. Each tablet provides all of the nutritional needs for an average adult for one day. The gruel doesn't taste particularly good, and the person feels hungry again right away. But, most people rarely eat anything else and the population stays fairly healthy (barring plagues, natural disasters and the occasional war).
In most ways, my people have reached a technological level about that of Europe in 1650.
The small planet has five island continents (think Australia), with urban centers mostly in the coastal areas. Ocean water is potable, so there is plenty of water for everybody. Unfortunately, there are no aquatic animals.
On four of the five continents, most of the land is also very barren. The largely barren continents have pockets of fertile soil, in which various crops can be grown. Every continent also has indigenous large herbivores that eat the few plants that grow wild on that continent, plants that can't be digested by my people.
The fifth continent is nearly overgrown with a fast growing plant that is processed to make the tablets. The plants cannot be made to grow anyplace else but on that continent. (There is magic involved here, the nature of which will be revealed towards the end of the story.)
The total population on the planet is about 100 million people, with the population pretty evenly split among four of the five continents. Each continent has a monarch and nobility. The monarch and nobles own all of the land and everything it produces including the wild animals (meat). Poaching or stealing of food other than the tablets is punishable by death on all five continents. Three of the continents deal in slaves and on the continent that makes the tablets, almost all of the (grueling) work is done by slaves. The two other continents on which slavery is legal get a lot of tablets in exchange for slaves. Slaves on my planet are slaves for life, as are their progeny (even if the other parent is a free person).
Food other than the tablets is scarce. Peasants are lucky to eat real food a few times a week, slaves never do. On the other hand, few nobles have ever tasted tablet gruel.
The monarch and most of the nobles on the continent that produces food are extremely rich, extremely powerful, and solidly evil. They like things as they are and want to keep them that way. The fifth continent has its royal family, perhaps 300 rich and powerful nobles, a few thousand pretty darn comfortable peasants, and 50,000 slaves.
My story begins at least 150 years later, at the cusp of an industrial revolution. I want the economy of my little planet to have been fairly stable for the past 150 years.
It is here that I ask the question:
How can I keep this economy stable for at least 150 years (200 to 250 years is better)?
I figure that the tablets have to be produced at a rate of at least 100 million per day (every day), but the average day will produce enough so that basic necessities can be purchased with small caches of tablets. As a rule, tablets are not hoarded even by the rich. Wealth is accumulated in the form of 'stuff'. Additionally, my people have the sense (or perhaps I can address the issue later as a matter of biology) to keep the population stable.
This currency is mostly consumed as quickly as it is "minted".
I am not averse to using magic to make things work, but I'd like to keep it pretty subtle. Magic is not a day to day concern of people not involved in the manufacture of food tablets. The world has a significant maritime structure that has evolved because of the tablets. It's a small planet, the sailing distance between continents is only a few days. So, 'spreading the wealth' is a non-magical industry important to my people.
OH! And as far as my people suspect, they are the only 'intelligent' people in the universe.
(Yes, this question was inspired by The Force Awakens.)