Reference point
Open a jar of mẻ and smell the surface.
Do this before you read on. An entry only works when you have just smelled the thing.
Harshly sour, with a note of cold cooked rice and a clear yeasty layer. It is sharper than pickled greens and less sweet than fermented sticky rice.
This entry shows one ingredient — cooked rice — going in three different directions. Fermented sticky rice turns into alcohol, spoiled rice turns bad, and mẻ turns into something kept deliberately.
The line between good and bad mẻ lies in the smell, and the people who keep it recognise it at once.
How to smell it
Smell the surface first, then stir and smell again — the lower part is stronger and more yeasty. If you have fermented sticky rice, smell them in turn to see two directions from one ingredient.
Why this one is hard
Because mẻ is disappearing from city kitchens. Many young people have never seen a jar of it, so they have no reference to compare against.
Don’t confuse with
This entry
Fermented rice starter
Fermented family
Both start from cooked rice. Mẻ is harshly sour and not sweet; fermented sticky rice has ethanol and esters, so it is sweet and warm.
Scientific note
Mẻ is a mixed community of lactic bacteria and yeast, fed continuously with cold cooked rice. Lactic acid gives the sour taste, while acetic acid — much more volatile — gives the sharp sourness the nose picks up; the yeast makes small amounts of ethanol and esters. It is one of the few Vietnamese fermented foods whose culture is kept and passed on for years, like a sourdough starter.
In Vietnamese life
Mẻ is used in sour soups, crab soup and braises. A jar can be kept going for decades and is often shared with neighbours when someone starts a new one — a custom almost lost in cities.