I just can't understand the fault in it, even by the explanations.
Sugar cane and sugar beet essentially of sucrose and used as a sweetener in food and drink.
Your problem is with the phrase 'essentially of sucrose and used...' 'Beets' should be plural and sugarcane is one word.
Sugarcane and sugar beets CONSIST essentially of sucrose and ARE used as a sweetener in food and drink.
That takes care of the grammar, but sugarcane has about 12% sucrose content, so 'essentially' doesn't logically work. The sentence also says that sugarcane and sugar beets are used as a sweetener, but it is the sucrose that is used.
Sugarcane and sugar beets contain sucrose, which is used as a sweetener in food and drink.
|link comment||answered Mar 12 at 14:29 Lewis Neidhardt Grammarly Fellow|