Fats in grass fed dairy and beef are far healthier than from corn fed animals, so this is important.
Kirkland has 25% less salt, so Kerrygold wins in a taste test.
But Kerrygold has 17% milk solids, while Kirkland has 10%. Milk solids cause butter to burn:
Milk solids are the reason butter starts to burn at a lower temperature than something like olive oil. When you clarify butter, you remove all the milk solids and water, but are left with the butterfat. This creates a higher smoke point, which makes clarified butter ideal for cooking and sautéing. (source)
Kirkland brand says 95% grass fed. I’ve read that Kerrygold cows are fed hay for a month or so during Irish winters, which is supposed to be why they are also not 100% grass fed. But they’re apparently not at anytime fed with corn, which changes the fats omega content to be less healthy.
Also, grass fed cows produce yellow colored butter from beta carotene in the grass. So the yellower the better.
I was kind of excited to see a Kirkland® brand of grass-fed butter being sold at Costco, but is it better than KerryGold®? Watch this video before you buy grass-fed butter!