Portuguese to English Science Chemistry; Chem Sci/Eng

The 'sob pressão' part is giving me some trouble.
First I thought it was a reference to the pressing of the plant to produce the oil but it seems to refer to the pressure applied in separating/producing the ethyl esters. So the problem is how to insert the pressure reference in the sentence:
"pressure ethyl esters" sounds wrong
"ethyl esters under pressure" sounds wrong because of what comes after "...under pressure from the oil"
I can't find any online examples of this particular expression.
Suggestions please...