title_body: Does aeropress coffee change flavour after several hours?
upvoted_answer: All coffee changes taste over time - it is full of relatively fragile organic compounds that will change over time. 
  
  Even in a vacuum flask (without exposure to light), the coffee will keep chemically reacting with itself. There is also oxygen in the bottle which will aid the breakdown of various of the compounds.
  
  There really is no way to perfectly preserve the taste of fresh coffee unfortunately!