What is meant by the line in 'The Crucible' where John says to Elizabeth just after an argument, "Your justice would freeze beer?"

The author is using a colorful figure of speech to express John Proctor's belief that his wife Elizabeth's practice of justice is cold and harsh; lacking mercy and forgiveness.

John Proctor has cheated on Elizabeth, but although he has confessed and repented, she cannot let it go.  She says she has forgiven and forgotten, but still acts with bitterness and suspicion.  Elizabeth says to John, "I do not judge you...I never thought you but a good man", yet her cool distantness towards him says otherwise, and he responds, "your justice would freeze beer!"

John does not feel that Elizabeth has forgiven him.  In answer to  her verbal protests to the contrary, he elaborates in explanation,

"Spare me!  You forget nothin' and forgive nothin'.  Learn charity, woman.  I have gone tiptoe in this house...I have not moved from there to there without I think to please you, and still an everlasting funeral marches round your heart.  I cannot speak but I am doubted, every moment judged for lies, as though I come into a court when I come into this house" (Act II, Scene 1).