Concentrates are a modified form of a sauce or stock, that try to reduce the water content without damaging the rest of the food. (as usually happens if you boil food for several hours, see the 'Common problems' section below)
Reducing the water intensifies the food's flavor.
Below, I only list the strongest form of each sauce available.
Concentrates that are my favorites:
Other concentrates that I like:
Ones I definitely don't enjoy include — Marmite/Vegemite,
Things I want to try, to see if they might be interesting to me.
Regardless of manufacturer:
Specific manufacturers:
Concentrates can be difficult to make at home, especially if they require use of a vacuum evaporator (as tomato concentrate does) or freeze drier.
Both of these processes (vacuum evaporation and freeze drying) intensify flavor by reducing the water content.
This is crazy, but apparently it's not impossible to do vacuum evaporation at home. [part2] [part2-archive] [part1] [part1-archive]
Boiling and even simmering a sauce (called 'reducing') for long periods of time can cause delicious volatile compounds to evaporate along with the water [2].
Even if you eliminate volatile evaporation, there's still the problem that heating a sauce for a long period of time can greatly modify the flavors in-place. Inherently, the sauce is being cooked the entire time. (In some cases, that extra cooking is thought to be inherent to the food's final taste, as happens with apple butter. But it doesn't have to be inherent. What would apple sauce that was vacuum-evaporated taste like?)
The sole goal is to remove some water. Other changes that happen at the same time may be undesirable.
There are many foods that can not be freeze dried, including fatty meats, butter, honey, jelly, etc.
TODO: Is it possible to remove a smaller portion of the water content, not 96% of it?
Concentrates usually seek to reduce the water content. Are there other things that one could try to remove, without altering the flavor, such as oils? (is it even possible to evaporate oils without evaporating the embedded volatile compounds?)