WordNet records no synonym and no antonym for top fermentation. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a violent kind of alcoholic fermentation at a temperature high enough to carry the yeast cells to the top of the fermenting liquid; used in the production of ale
“top fermentation uses a yeast that ferments at higher temperatures than that used for bottom fermentation”
Synonyms, antonyms and the broader and narrower relations for top fermentation come from Princeton University’s WordNet. Full sources and licences.