Butter isn't a chemical mixture. It's a food made from a living animal. As with all things in nature, it will vary depending on the animal and its health. This kind of reductionist and industrial attitude towards food is detrimental to nutrition and overall. In our aim to standardize everything, we've forgotten the animals and the farmers and our connection to food. In an agricultural society you would have been laughed at if you said "isn't all butter the same?"
Well, I have nothing to go on but the label, which is reductionist in the extreme. Which is why I ask what the difference is. I'm really most interested in the qualitative difference, not the exact amino acid composition. Sibling comments inform me that Kerrygold is more delicious than what my grocer stocks. In what way? What is different about the manner in which it's produced?
Most dairy cows in Ireland (where Kerrygold comes from) are Jersey cows, the fat content of whose milk is higher to start with, which makes it smoother and gives it a yellower color. There's also a little more salt in it, I think.
But as I said the label will only take you so far. If you want to know what something tastes like you need to put it in your mouth and chew it for a while. If you're not willing to experiment then you're going to miss out on all kinds of delicious things. The price of sometimes buying things and discovering that you don't enjoy them is well worth it.
