Subject: What happens when mixing sucrose and tartaric/citric acid?

Hi, at first great project (!!!) and thank you very much for doing this!
I'm asking because I'm trying to understand a chemical reaction I've observed in
my kitchen, when trying to make sugar-based crash-glass.

The basic experiment: destilled water, sucrose and either citric or tartaric
acid are heated in a pot up to around 140°C/284°F, just before it caramelizes.

I know the following from previous research and experimenting:
- The acid splits the sucrose into glucose and fructose, which act as
interferring agents (as do the 2 acids themselves, hydrogen bridges...) and
prevent crystallisation.
- The mass is less hygroscopic than without the acid.
- The mass already turns slightly yellowish (with tartaric acid less than with
citric acid) just before reaching the caramelizing-temperature. It doesn't
happen without an acid or with vinegar.
- When cooling down the mass takes longer to cure than without the acid (much
more suited for shaping).

My theories with regard to the last three points:
- The structures of sucrose and citric/tartaric acid fit together very good
(less free OH-groups attracting water).
- Maybe an ester is formed. The 2/3 carboxyl-groups hold the possibility of
building polymers causing the color -> delocalisation. Maybe the acid just
reacts with itself (just heat the acid and it also turns yellow).
- Also hydrogen bridges, but I don’t really have a concrete idea.

Can you explain what causes my observations (last three points)? Is an ester formed?

Re: What happens when mixing sucrose and tartaric/citric acid?