To “cut the mustard” is an odd term of uncertain origin. There are several theories as to its possible source, some seemingly credible, while others seem less credible. Some of the more literal theories support a case that it’s actual mustard being cut, in the form of either seeds or plants; a difficult task which, if accomplished is considered good.

Another suggested theory is that the phrase is simply an altered version of the military expression 'cut the muster'. This appears believable at first sight. A little research shows it not to be so. Muster is the calling together of soldiers, sailors, prisoners, to parade for inspection or exercise.

To cut muster would be a breach of discipline; hardly a phrase that would have been adopted with the meaning of success or excellence. This line of thought appears to have been influenced by confusion with the term 'pass muster', which would have the correct meaning, but which could hardly be argued to be the origin of 'cut the mustard'.

“Up to mustard” or just “mustard” means up to standard in the same way as 'up to snuff'. 'Cutting' has also long been used to mean “exhibiting”, as in the phrase “cutting a fine figure”. Therefore, the derivation of “cutting the mustard” as an alternative way of saying “exhibiting one's high standards” is the most likely origin.