The pyruvate scale measures pungency in onions and garlic with units of µmol/gfw (micromoles per gram fresh weight). It is named after pyruvic acid, the alpha-keto acid co-product created in the biochemical pathway that forms syn-Propanethial-S-oxide, the main lachrymatory agent in onions. The standard onion has an eight rating, while "sweet onions" have a two or three rating on the scale. The lower the score or scale the more "sweet" the onions are rated. Anything less than five is considered a sweet onion.