For those not in the know, here's the Wikipedia page on perpetual stew. The one with which I'm most familiar with is Welsh cawl, not that the recipe cited is a perpetual version.
I can think of certain advantages to a perpetual stew including:
economy
ease of cooking
However, I also presume there were certain drawbacks.
what would the effects of spoilage be? No matter how well you try and mix the ingredients in the pot, there will always be some residual food from previous days/weeks. Surely this had a spoiling point, and therefore could contaminate the rest of the batch?
if spoiling of a perpetual stew happened, how was the dish "restarted", for lack of a better word?
were there nutritive drawbacks (not every diner is guaranteed the same ratios of foods in each portion)?
I've deliberately not specified a period/place for this question. Many thanks for your input. EDIT: formatting to make bullet points work
what would the effects of spoilage be? No matter how well you try and mix the ingredients in the pot, there will always be some residual food from previous days/weeks. Surely this had a spoiling point, and therefore could contaminate the rest of the batch?
For the most part, food doesn't spoil due to just sitting around, it spoils due to the contamination by microorganisms as shown by Louis Pastuer in 1859, when he demonstrated that microorganisms do not spontaneously generate in food that is sterilized then sealed from outside sources of contamination.
As long as the stew is continually heated there will be little to no chance for microorganisms to grow and "spoil" the food. Barring the case of extreme themophiles (which inhabit hot springs and volcanic vents, not cook pots) bacteria are killed when brought to a boil.
That being said, almost all spoilage is due to some kind of bacteria or pest getting into the food. If nothing can live in the food then it won't spoil.
Pickling for instance is a way of preserving food by storing it in a vinegar solution, which prevents bacterial growth, but is harmless to us. Another way to make "Preserves" is to reduce the water content of fruit by drying or boiling off the water until the sugar content is so high that bacteria can't survive (jams jellies and dried fruits). A third way is Salting which also makes the food inhospitable to bacteria, but edible for us.
The Perpetual Stew would avoid spoilage by being brought to a boil whenever new food is added.
Sorry if this is more Science than history... it is what it is.
This may be more of an /r/askculinary issue than /r/askhistory.
Here is an excellent series of videos on cooking in the 18th century. It does not show a perpetual stew but it does show cooking over an open fire. Note that many recipes for puddings call for boiling them for 3, 4 hours or longer. This was not a problem when you have a fire going all day.
Jas. Townsend and sonhttps://www.youtube.com/user/jastownsendandson
Boiling a puddinghttps://www.youtube.com/watch?v=SzH5B0T2GYU
Notice the wood fire in the background. Even burning a few small pieces of wood, you can see you can't turn the fire on and off like a modern range. It takes time for a fire to burn down to coals and then it burns a long time. It would be natural for cooks to invent recipes to take advantage of this long lasting heat source.