These are crystals formed by the stirring rod scratching a saturated mixture which then begins to form at the site of the scratch. It is well known to Organic Chemists that they must scratch some mixtures to begin precipitation or crystallization. As for why this forms in one case and not another, it may be due to a salt being formed in one that is not in the other.

BTW, very nice work on the concentrate. The results look great.

PE