All about butter

This listing is not mine, but I approve them all. I found the list in a stash of emails I was about to delete, and thought I'd share it. It may be from The City Cook, but I can't find it on their site.

Butter Basics

• Butter is made from 100% heavy cream that has been agitated so to separate water and butterfat. The fat left behind is butter. The watery liquid that is removed is buttermilk or whey. Contrary to its high-cholesterol sounding name, buttermilk in fact is very low fat which makes sense if you consider how it's produced. 
• Nearly every butter available in our stores has been pasteurized.
• Unsalted or sweet butter is exactly as its name suggests. Butterfat without any added salt.
• Salted butter includes one to two percent salt (that's like adding one to two teaspoons per pound). Some salted butters include grainy salts like sel de fleur, giving the butter an almost crunchy texture and a more aggressively salty taste.
• European butter has a higher butterfat content -- as high as 86%. This is in comparison with regular butter, which will have a butterfat content of about 80%. More butterfat means less moisture and this translates into a denser, more refined texture and when used in baking, it can produce flakier pastries. In addition, some European butters are made with cultured cream and due to the addition of lactic acid bacteria, it has a more forward, bigger flavor. A few butters made in the U.S., including one by Cabot, will be labeled "European" as a way of declaring its higher butterfat content.
• Organic butter is made with cream that's been certified organic and antibiotic free.
• Whipped butter is simply butter to which nitrogen has been added which means it is softer to spread. But keep in mind that the whipping also reduces volume so you're actually getting less product for the money. If you love whipped butter, especially on pancakes or scones, just let a stick soften to almost room temperature and then whip it yourself using a hand or stand mixer. 
• Truffle butter is plain butter to which bits of black or white truffles have been added. Two popular brands are d'Artagnan and DaRosario and a little 2 oz. container usually costs $10 to $15. And what's the point? Well, if you are a truffle lover and with truffles costing the price of Caribbean vacation, a tablespoon of truffle butter tossed with a bowl of fettuccine (use dry pasta and search out DeCecco's, making sure it's the egg fettuccine), or added to scrambled eggs, or glossing plain steamed green beans will satisfy many a craving.
• Clarified butter has been melted so as to separate its water, milk solids and pure milk fat, producing a clear yellow liquid. By removing the water and milk solids, the remaining liquefied milk fat will not burn as easily, making it a good choice when butter is used in higher temperature frying.
• Ghee is the name in India for clarified butter that has been additionally cooked, adding more complex flavor and extended stability (ghee can keep unrefrigerated for many months). It also has cultural and religious importance.
• Compound butter is a term used to describe a butter to which flavorings have been added. Truffle butter is one but more quotidian examples would be made with garlic, minced tarragon or other fresh herbs, chopped shallot, or ground cinnamon. It's simple to make: use a fork to mash together softened butter with the ingredient of your choice and then refrigerate until ready to use.
• Countries that have dairy legacies, such as Ireland and France, deserve their reputations for really excellent butter and flavors can subtly vary depending on the grasses the cows eat. Butters from Ireland, Normandy, Brittany and Holland are exported to the U.S. and are increasingly easy to find in our grocers and specialty markets.