I don’t think there’s very much in common at all between HMJ and YM, except they both fall within the general category of bittersweets.
As far as the tannins are concerned, YM is an outlier amongst other bittersweets, for two reasons.
1. YM has relatively few procyanidins (aka tannins) compared to its content of phenolic acids and is unusual amongst bittersweet apples for that reason. So it’s a very mild bittersweet to the taste. Milder than chemical analysis would suggest.
2. The composition of YM phenolic acids is unusual also, and comprises mostly p-coumaroyl quinic esters compared to mostly caffeoyl quinic esters in other apples. The pCQ esters break down under the influence of malo-lactic bacteria to give ethyl phenol rather than ethyl catechol aromas. Ethyl phenol has a lower flavour threshold than ethyl catechol. This may be the reason why YM seems to give “farmyard” aromas so readily, though I suspect there may be other factors at play here too which have never been investigated.
These observations don’t directly answer your question though they may provide some background. For my part I have both YM and HMJ and I would not trade one for the other - they are both valuable in a blend for different purposes.
Andrew
Wittenham Hill Cider Page