Saying an ISA is just a hardware API vastly oversimplifies what an architecture is. There is way more to it than just the instruction set, because you can’t have an instruction set without also defining the numbers and types of registers, the mapping of memory and how the CPU interacts with it, the input/output model for the system, and a bunch of other features like virtual memory, addressing modes etc. Just to give an idea, the ARM reference is 850 pages long.
The actual acid (acetic in vinegar, citric in citrus and tomatoes) actually boils off with the water. So a long simmer actually removes the acid and changes the pH of the dish.