Is it permissible to exchange 8 loaves of barley bread for 10 loaves of wheat bread, while paying the baking fee?

The aforementioned transaction—paying wheat flour and a fee to the baker in exchange for barley bread given by the baker—is impermissible. This is because it involves exchanging wheat flour for barley flour without immediate possession (taqabudh), which is not permissible for usurious commodities (ribawi items) like wheat and barley. To correct the transaction, one must give the wheat flour to the baker and take its value in barley flour hand-to-hand immediately. Then, leave the barley flour with the baker for him to bake, based on the saying of the Prophet (peace be upon him): "Sell wheat for barley as you wish, hand to hand."