Let me give you my conclusions at the start, and I will elaborate further down the post. Don's starter may be:-
1. An absolutely unique starter derived from Saccharomyces Cerevisiae yeast instead of the more common Candida Milleri yeast, without any of the characteristic sourdough flavours.
2. It may be that Don has been given some unusual instructions regarding the creation of a starter.
3. Don may have been given some starter that has not been started with the correct instructions.
4. Don has jokingly decided to do an old sourdough bakers trick of sending what is purported to be a sourdough starter, but is instead a commercial yeast starter, just to see if the recipient knows the difference. I can take a joke.
What I am saying is that while it has produced a lovely tasting bread, and without the benefit of chemical analysis to prove otherwise, I consider this starter to be based on commercial yeast.
I'm a firm believer that "If it looks like a duck and walks like a duck etc etc".
On receiving the starter I rehydrated it with my usual method. It became active very rapidly (1 hour) compared to other starters I have rehydrated.
On reaching what I consider to be working strength after several refreshments, it had a very strong "Beer" smell, unlike any of the other starters I have.
When I first read Don's recipe I was quite suprised at the proofing times he quoted and was unable to reproduce those short times using my starters in my first two attempts at this recipe. However with Don's starter these short times were reproduced.
I thought I could feel a little difference in the proofed dough at shaping time but didn't think much about it at the time. My suspicions first really became aroused when I smelt the loaves baking. Those who know me personally will vouch for my acute sense of smell and taste.
When cooked the crust was noticeably different to usual, and on tasting my suspicions were confirmed, characteristic commercial yeast taste and aroma, and a complete abscence of anything resembling a sourdough taste.
Now I may be completely wrong it may be that this starter was created with some grapes or raisins or some other fruit, because saccharomyces cerevisiae (the yeast that produces beer, wine, and bread) is particularly attracted to these. But I still cant explain the lack of any flavours produced by a Lactobacillus of some type. (49 different ones identified to date).
So based on, it acted like a duck, it felt like a duck, it smelt like a duck, it tasted like a duck, and it didn't taste like pork, I would have to say it was a commercial yeast based starter, or something damned close to it.