• Extra Virgin, Virgin, First Cold Press - use for low temperature only, including low temperature frying such as wilting onions, etc. At higher temperatures the flavoring elements degrade (into what nobody knows) and the flavor is lost even below 300°F.

  • Pure Olive Oil, Olive Oil - olive oil refined from oils that didn't meet the stringent Extra Virgin acidity spec or second pressing. May be blended with some unrefined oil for flavor. Little olive oil flavor in most. Use for moderate temperature frying below 400°F.

  • Pomace Oil - refined from oil extracted after cold pressing. No olive oil flavor but goes to high temperatures for deep frying applications (smokes at 460°F) and the like, and for use in recipes where no olive oil flavor whatever is desired. Some Pomace oil has a little extra virgin tossed in to restore some flavor, but usually very little.
There is no significant difference in the fat profile of these three grades so the basic health benefits are the same. There may be some small side benefit from some of the flavoring components of Extra Virgin (no significant research), but Extra Virgin doesn't work well in emulsified sauces.

Oh, yeah, I'm a real acid freak, so I mix my dressings 50%/50% or even higher on the vinegar. Use real good quality vinegar - my favorite is malt or an apple/balsamic mix (apple is too harsh and balsamic is too sweet). Rice vinegar is good too, and of course quality wine vinegar.

Many people make strong health claims for vinegar, particularly apple vinegar, but little research has been done. Note, most "Apple Cider Vinegar" is fake - distilled vinegar with apple juice added. Heinz makes real apple vinegar in quart jars - their larger sizes are fake.