Joseph kayeri asks:
How does the gemara proves from the beraita that mekach does not kovea lemaaser? It can be that mekach indeed kovea, but here the buyer can eat from it in an arai form and need only to separate maaser demai because the majority of amei haaretz do separate maaser from their crops even from produce that did not complete their production (as Rashi points out).
Joseph kayeri, Sao Paulo brazil
The Kollel replies:
If Mekach makes Keva, then all eating is considered Keva and no Arai exists at all, even by Demai and no eating is allowed before Ma'aser.
All the best,
Reuven Weiner