What words in the poem "The bamboo stove soup boils at the beginning" describe the cold at night?

What word is used to describe the cold at night in Bamboo Stove Soup Boiling Fire?

If we must find out the correlation, there is only the word "red initial fire"

On a cold night, guests come to tea for wine, and the bamboo stove soup is boiling red at first.

A Cold Night by Du Lei in Song Dynasty.

On a cold night, guests come to tea for wine, and the bamboo stove soup is boiling red at first.

As usual, there are plum blossoms in front of the window, and there are plum blossoms before the month.

translate

There are guests visiting in winter night, and a cup of hot tea is served as wine. Sitting in front of the stove, the charcoal fire in the stove has just turned red and the water in the pot is boiling.

Moonlight shines on the window, which is no different in peacetime, except that some plum blossoms bloom faintly in the moonlight.