Oil Or Butter? Please Help Me Understand Their Effects.
Decorating By Mb20fan Updated 18 Mar 2014 , 12:21am by hbquikcomjamesl
Hello all...I'm a newbie! This is actually my first post in the forum and I hope I find success in getting my question answered or discussed. 
OTHER THAN TASTE:
Why do some recipes call for oil and some call for butter? If you want a moist cake, is oil better? If you need density, is butter better? I'd love to explore what the advantages are to using each. Again, not looking for the obvious (taste or health reasons), moreso trying to learn how it affects the outcome of the cake as far as it's texture, moistness and density. ANY input would be appreciated. Thank you kindly. 
Shay
Welcome to CC. We do have some chemically minded members here - so hopefully they will see your post and help answer. I wish I could help.
It seems to me that Indydebi would be the one with a good answer!
Either that or Alton Brown would know for sure!
My understanding is that the purpose of the fat is to coat the protein molecules in the flour, thus inhibiting the gluten formation (too much gluten makes a tough baked good).
Oil coats the protein very well and gives you a very moist feel to the cake. It is a bit of an illusion because it's actually an oily residue, if you will, but our mouth translates that to moist. However, oil doesn't function like butter in cakes because it doesn't get "whipped" with air trapped in for the rising... and as you mentioned, it doesn't come with as robust a taste.
Butter also coats the flour, but not quite as fully, especially not in the creaming method. If you use the method where you beat the butter into the flour and sugar, etc, and then add eggs and liquid, you will get a better coating and a nicer crumb, a more moist feeling. However, you will not have as big of a rise.
This is because in the creaming method, the fat is being punctured by the sugar (which is why you have to cream for at LEAST 5 minutes) to allow the steam to expand those holes later, giving you rise. However, this method leaves you with a denser feeling... and can feel tough if you overmix the flour in at the end.
Butter is also part water, which creates the steam. It also does add some liquid to your recipe, which is why you can't just swap out butter for oil or shortening in most recipes.
I prefer butter for the taste, and I do both the creaming method and the other (can't recall the name) depending on what result I'm after.
On the rare occasion that i do use oil, the cake is more like a box mix cake in terms of mouth feel. It's softer, usually, less sturdy in my opinion, more "moist" but it lacks flavor.
**** Please note, I am far from an expert, but do my best to self-teach the science of baking. 
If I am off on something, someone please correct me!!
Both are fats so they work in somewhat the same way. They are tenderizers. Oil will add tenderness because it never gets solid. Butter on the other hand bonds with sugar crystals to hold air. Look at it this way. Muffins are dense the fat is liquid, most of the time it is butter. Melted butter will not hold any air.
As for texture if a cake with butter isn't cold where the butter resolidifies they are pretty much the same.
Oil will leave a film in your mouth. Butter has a melting point lower than your body temp. Butter will have a better mouth feel.
Mike
Ok, I dork out bad on science stuff. And I'd probably leave my husband for Alton Brown (though, to be fair, my husband would probably trade out his sexual orientation for Alton Brown. lol). So I just had to say that I am LOVING this thread. Even if I am worthless in adding anything to it. : )
Wow! Thank you all for replying! I've enjoyed reading all of this and it's quite helpful (and impressive).
So far, what you guys have said about how oil seems to produce what we like to think of as a moist cake is exactly what my experiences have been. Now based on what has been said so far, I'm wondering something else:
If both seem to bring different yet beneficial attributes to the table, why can't both ever be used together to get the best of both worlds? Taste and moisture?
I would assume that if you are baking cakes to be in tiers, you should opt for density, therefore go with butter, right? Can any of you share in which baking situations (other than muffins) you opt for one over the other (stacking cakes or not)?
Thanks again! I REALLLY appreciate the input!
Moistness comes from your liquids. I would keep oil in the fat catagory. Oil effects texture more than moistness. I don't use it. Even in the rare instance of using a box mix I subtitute bvutter for oil. You could toss oil away, and it would never effect my baked goods at all.
In baking, sugar is a liquid.
Mike
One odd thing that I've learned is that if you leave out most (or even all) of the oil called for in a boxed cake mix, the cake is just fine. It is less "crumby" on its surface, so it can often be frosted without a crumb coating. The mix already has some oil in it. Usually what I do now is put in a Tbl or so.
I do know that butter has water in it--hence 100 calories per T of butter vs 120 calories per T of vegetable oil.
Here is a link that explains it better than I can. I personally don't believe you get the same results and can just sub in oil for butter or vice versa without a change in texture. I love the book "The Science of Baking" it's my "go to" and is well worth the investment.
Check this out: http://www.baking911.com/pantry/fats.htm
Article on butter at Joy of Baking, unfortunately, they do not have on on oil.
http://www.joyofbaking.com/Butter.html
AI have a question based on the above in for and other people's experiences. A friend of mine has had me make multiple cakes for her and all different flavors... chocolate, pumpkin spice, and egg nog. The chocolates uses oil and the other two use some butter. I made her a yellow cake the other day with 1.5 sticks of butter. My husband and I thought the cake came out wonderful and ate both tops that I cut off the cake...seemed moist and delicious. Spoke with her today and excited to find out about the cake only to have her reply it was a little dry and the middle crumbled a little bit. She went on to mention it wasn't dry like over baked. I was shocked! From hearing the other notes I believe the cake may have just been a little more crummy then the other cakes that I had made that either used oil or less butter.
Does anyone have any thoughts...could it just be the difference in consistency that maybe their not use too? I also usually use all purpose flour and this recipe called for cake flour. What has been your experiances using cake flour vs regular flour?
The closest I've come to a scratch cake was once, using a recipe that used to be on the back of the Bisquick box.
But I've noticed that in the mixes available today, the only one I've used that calls for butter is the BC pound cake mix. Everything else I've used (including waffles from Bisquick) calls for oil.
On the other hand, all my cookie recipes call for butter, margarine, or some combination of the two.
And these days, when I make Rice-a-Roni, I always make it with a combination of butter and Canola oil. (If, as the package directions on the "reduced sodium" version, I just use half the usual amount of margarine, it ends up a bit sticky, but combining butter and Canola seems to produce the best flavor. For poultry dressing, on the other hand, I use a 50/50 mix of unsalted butter and salted margarine to saute the onions and celery.)
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