Only after the coffee goes in the big container full of lots of other coffee is it rendered unidentifiable. If the coffee vendor didn't pour the stolen bag of beans into the rest of it then it's still clearly identifiable.
Bitcoins are not quite like the a banknote. If I have a $1 and $20 bill that's 2 things each with a serial number. I can give them to you, and you can give them back to me. Bitcoins on the other hand don't work that way. The movement of them changes them, even though you can trace the flow of the value represented.
Let's say someone steals your 1 bitcoins, sending 0.999998 bitcoins to himself, leaving 0.000002 bitcoins for the miner who confirms the transaction. Then the thief sends 0.999996 bitcoins to someone totally innocent in exchange for a car, leaving another 200 satoshi for that miner.
You find the person who sold that car for those bitcoins and he still controls that balance. Are you entitled to get those bitcoins back?
Well, say the car seller had no other bitcoin. One argument would be that he still has 0.999996 of your bitcoins, so he's obligated to give your property back and he needs to figure out how to collect for the car, tough luck for him. The fact that he doesn't have it all is no different than if his car was stolen and he found just missing a couple of hubcaps.
Another argument could be that no, your bitcoins were the UTXO that you could solve the unlock script for, which you still can, so it's like the car seller had received an item that your bitcoins were exchanged for (new script). I don't think most people would have much sympathy for this argument.
But what if your coins were only 1 input into the transaction sent to the car seller, and then the car seller spent half of on his rent, receiving back the balance to his change address?
Now we've arrived at coffee beans. Even though you can know the balances, you cannot say whether your bitcoins are in the possession of the car seller or his landlord. It makes no sense to say that each of them has half, nor does it make any sense to claim that one or the other has your stolen property.
So assuming bitcoins do not have the special money status and stolen bitcoins are going to be treated like other stolen property is then they are like the coffee beans in that they become unidentifiable without anyone trying to be dishonest.