what to say when they ask "what variety is this?"

I have had this conversation no less than 18 times this fall.

1. here, try this apple.
2.  oh.  Tasty.  What variety is it?
1. it's a heritage apple.
2. what variety of heritage apple
1. It isn't a variety.
2. you don't know what kind it is?
1.  No.  It isn't a specific variety.  The tree is about 140 years old and shows no signs of being grafted.
2.  What variety is it?
1.  It's not grafted.  it's grown from seed.
2. But it's delicious.  I want to buy this variety in the store.  Can't you just tell me what variety it is?
1.  It's a Heritage apple.
2. oh.  

That's the condensed version.  The actual conversation lasts over half an hour and by the end of the history lesson on the medieval diet, how to apple biology and tree grafting, the early European settlers, the Crimean war, and prohibition combined with some clever marketing to save the apple industry - they seem to long for a more innocent time.  

There's got to be a faster way to get through that conversation.  

In my case I can honestly say "the tree was here before we bought the place so we don't know what kind it is".  In your case you could also try "it's a wild apple so it isn't available anywhere else in the world - I'm charging $5 per apple".

It's a Raven apple.

Name it.  Problem solved.

As an aside, I think it's definitely worth grafting more of the tree if the fruit is as good/well loved as it sounds.