- The extracts are added to the boil portion and hence saturate it. The hops cannot be as effectively absorbed. This can be avoided, in part, by not adding half of the extracts until the end of the boil (long enough to sanitize)
- Water needs to be added to the wort in the fermenter to bring it up to full size, rather than being incorporated in the whole boil. If you did this with a curry sauce, I doubt it would be as flavorful.
These contribute to the extract twang. This is where the smaller batches are advantageous: you can do the wort as a full boil.