butter/margarine vs. vegetable oil in cakes

[mudbug]

"1) I heard from my daughter that adding oil to a cake mixture gives more...humidity or moistened to it. Instead butter gives a drier consistency. I use oil only for chocolate cakes or carrot´s one, should i add oil to any of my recipes to get them moistened? i mean that if it's probably or convinient to substitute or mix a fraction of the butter for oil.

2) As humidity is an enemy in my country, do you think that using "propianate of Na" ie. would really help me to maintain freshnes of cakes and other products that are sold in my bussiness? does it change the quality of the product?"

leyla

It is true that oil does make a cake moister and more tender because it is more fluid in a cake batter, coating flour particles much more than butter. I like replacing a portion of the butter with oil, so as not to lose that butter flavor. Even my muffins are part butter part oil. Shirley Corriher's Cookwise was an excellent source for me on this idea.
One thing to take into account is that butter is about 80% fat and 15 % water, and oil is 100% fat.

I made a lemon poundcake and replaced about 30 % of the butter with oil. The texture of the loaf was much softer than all butter, yet the butter flavor came through loud and clear.