I've been baking bread for years and no longer really measure the ingredients. But I'm no expert on the science of what I'm doing. I add fat (lard) because I've always added fat.
What job does the fat do? And if I have long been using too little or too much fat how would this affect my loaf?
And then, writing this up, I'm also wondering about yeast. I guess if I use too little yeast I am going to get a loaf which rises insufficiently. But what would be the consequences of using too much yeast?
Amongst other things, fats help moderate/impede gluten development, by not allowing water to activate the proteins.
Too much yeast and your dough will be flabby and over-risen.
Weird, I never use any fat in bread dough. I always thought fat was a pastry or cake thing because it tends to make the crumb a lot denser as apposed to a wide open texture of say French bread. How much do you use? I'd be interested to try it.
The only time I do use fat is for Ciabatta, Pizza Dough or Focaccia, but then I use olive oil, which is a bit different.
As for the yeast. I've made the mistake of adding too much yeast in the past. I noticed that the result ends up tasting of yeast. But, if you add way too much yeast, you could also run the risk of the dough not rising properly as there won't be enough sugar/starch around to keep the culture alive.
Like Darin explains, it helps make your bread last fresh for longer. French bread will dry out within 24 hours, while Italian breads with ~5 spoons of olive oil (and other breads with butter and eggs) are good for 2 or sometimes even 3 days. I've also read that bread from olive dough (e.g. Ciabatta) feels better after baking+freezing+re-baking but I haven't tried enough times to asses how much of an improvement that is.
