Student or Learner
In regards to using the interjection mmm to describe food. Which of the following is correct
I don't think there is a "right" way to use it. Three "m"s seems about right to me, but you might see more depending on the length of the sound made. There are other issues with your sentences.
The first should not have a capital "b" on "burgers" because it comes after a comma. There is also no final punctuation mark.
Your second should not have a capital "b" on "burgers" because it comes after a comma.
The third is acceptable for me.
The fourth should not have an exclamation mark followed by two full stops. I don't know what punctuation you were aiming for.
The fifth would be OK if you put a space before the ellipsis (the three full stops) and change the first letter of "burgers" to lower case.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.