Oil is important enough that it should perhaps have its own page instead of just a post! Oil is a loose term used to refer to a wide variety of fats. More correctly, they are referred to as lipids. These terms can include solid fats (such as butter, lard or shortening) or liquid oils (such as a host of oils including Olive Oil, Canola Oil, Corn Oil, Hazelnut Oil, Sesame Oil and on and on and on).
Some oils, such as extra virgin olive oil, almond oil, sesame oil and hazelnut oil are used largely for the tastes they add to breads and other foods and are beyond the scope of this discussion. Enjoy 'em, they can be lots of fun whether they are incorporated into the dough, used in or as bread toppings, or used to dip bread in.
I choose my oils carefully and for a number of reasons. Are they healthy? Do they enhance the taste, quality, and/or keeping characteristics of the foods I prepare with them? Overall, I feel that we're omnivores, and that we are designed to eat anything that isn't quick enough to get away from us. I believe moderation is the saving of us. If we don't eat too much of any one thing - or too much at all - it's better for us and the environment. Still, I am suspicious of overly processed foods. Solidified liquid oils, such as partially hydrogenated oils, aka shortening, have long been suspect for me.
The recent revelations of the dangers of trans-fatty acids confirmed my prejudices in this area. I find it easier to avoid suspect foods. So, overall, I like foods that people have been eating for hundreds - or better yet, thousands - of years. Are the newer ways of solidifying liquid oils better than hydrogenation? I'm content to avoid these new foods and wait for more research to be done. None of this means I'm a neo-Luddite. I keep up on trends and research, at least at a layman level.
Getting back to baking, oils are added to bread to improve the crumb structure, the rise, and the storage qualities of the bread. Dr. Emily Buehler is a baker who first trained first as a chemist. She talks about oils at some length in her marvelous book, "Bread Science" which available through her web page twobluebooks.com. Dr. Buehler cites a number of studies which examine how the chemistry of dough and dough development work. The current theory is that lipids strengthen the bubble walls in dough. Interestingly, one study which showed solid oils did more to improve rise than liquid oils.
Further, it was the state of the oil that mattered. One of the tests in that study used the same oil in liquid and solid states and the solid oil helped the dough more.
While oils do improve the crumb and keeping qualities of breads, at times the improvement in those areas has a cost in others. Many breads are lean breads, and if oil is added the bread flavor changes. Some well meaning people add oil or milk to baguettes. The result is a different bread, and usually an inferior one. Baguettes should have layers of flavor - rich extravagant flavors from fermentation, caramelization flavors from the proper baking of the crust, and strong wheat flavors. Baguettes tend to lose these flavors when oils and/or milk are added and become long, skinny pieces of Wonder Bread. While the addition of oil can be beneficial, it is hardly a panacea and the use of oil has to be in keeping with the type of the bread.
Oils cause lots of debate. Here are some common questions/issues.
Should oils be added at the start of mixing dough, or at the end? If your bread is turning out right, you're doing it right. If not, try switching what you're doing. I've had it make a big difference in the results, but what works "best" seems to vary from bread to bread.
If I add oil to a recipe, how should I change the recipe? and What about switching from solid to liquid, or liquid to solid oils? In general, a good starting point is to substitute oils for water, on either a volume for volume or weight for weight basis. If you put in 1/4 cup of butter, use 1/4 cup less of water or milk. Liquid and solid oils are pretty much interchangeable in bread-baking as far as dough consistency goes. Again, if you add oil to a bread, you have substantially changed the bread, and not always for the better. You may find you prefer the bread without the added oil.
What kind of oil should I use? Following my hundreds - or better yet thousands - of years test, my preference is for lard, butter, and olive oil. Sadly, it's hard to get good lard these days, so I have avoided it. Many pastry chefs say there is nothing that compares with lard, so I suppose I should work with it some more. Unsalted butter works very nicely in many breads, and gives pastries a nice richness. And then there's olive oil.
Of all oils, olive oil is my favorite for all around cooking, although it is not a good choice for high temperature frying. Olive oil is recommended by many health experts because of its properties. It also gets me a fair number of upset emails. Olive oil? In Bread? Isn't it too strong? I've been told, "it's not appropriate" in a number of foods, such as Challah and granola. Now, please note I didn't say "extra virgin olive oil." I use EVOO (to use Rachel Ray's acronym) in some breads such as focaccia and ciabatta where I want the flavor that EVOO adds. However, there are a host of non-virgin olive oils that have most, if not all, the dietetic and culinary properties of EVOO without having an overwhelming taste. Many of these oils are quite reasonably priced. And they work just fine in Challah and granola. Or any place you want a mild oil. Some people ask why I use olive oil instead of Canola Oil.
Canola Oil doesn't meet my hundreds of years test. And, from what I have read, it is much more processed than olive oil and some people are concerned about it. So, I prefer the late pressing, second pressing or even pomace olive oils for my daily oils. Check with me in a few hundred years. Maybe I'll have reconsidered oils by then.