Can someone  please explain why by adding a knob of butter into the pan of water during the steaming of cabbage makes the cabbage taste better.   I understand this idea come from Denmark. I've tried it and for some unknown reason works and my friends have spotted the difference during a blind test I did.  
Some of the butter ends up on your food. Most people will think the flavor is improved if there's a tiny bit of salt and a tiny bit of butter flavor. We like fat, we like salt, and we like the actual butter flavor, though it's more subtle.  In case you were wondering why the butter ends up on the food... The oil melts into the water boiling on the bottom. It'll be trying to sit on top, but with the water bubbling and boiling things mix a bit. Either way, little droplets are definitely going to get thrown around. A bit of butter, or even most of it, is going to end up on your food.  You can easily prove this to yourself - the residue on the sides of the pot will also be greasy, and if you boil away all the water after you remove your cabbage, there won't be nearly as much melted butter as you started with. You can also see this if you're cooking things in just oil (with a bit of water coming off the food). As things splatter, you get a lot of oil droplets flying everywhere, which I'm sure you've noticed when you're cleaning in the kitchen. Actually mixing oil and water just makes this even more pronounced.  I'm not sure how you do your steaming, but if you're taking a shortcut, skipping the steamer basket, and just putting a bit of water in the bottom of a pot or pan, even more (probably most) of the butter will end up on the food. 