The grains of Arabica and Robusta differ primarilycaffeine: Arabica - 0.9-1.4%, in robusta - 1.8-4.0%. Chlorogenic acid, coffee provide astringent taste, robusta more - 10% arabica than - 6.5%. So the taste of pure Robusta is more pungent and astringent. But fatty acids in greater Arabica - 16% Robusta than - 10%. Therefore Arabica coffee is more viscous and dense.
In modern industry never use pure grade. Typically, prepare a mixture of arabica and robusta coffee with the addition of some other varieties.