No, it isn't actually necessary. The yeast activates just fine with the moisture in the bread. I've been using Active Dry Yeast for years and hardly ever bother with proofing it.
Proofing shows that the yeast is actually alive. If you have any doubt about it, proof it as the first thing that you do, before mixing up the other ingredients (and especially before putting liquid in). If it fails then you didn't waste materials.
There are three major properties of the liquids:
- Fat based (oil, melted butter, bacon drippings, and on) versus water based (milk, juice, water, and so on).
- Flavor - some liquids, juices and to a lesser extent, milk have a distinct flavor that will effect the bread
- Acid - Some liquids, like orange juice, are more acid and affect the pH of the dough
Not every liquid falls neatly into these exact categories. Milk, for example, is about 87% water, 4% fat, and the rest is sugars and proteins. These differences are often insignificant compared to the overall bread recipe.
In general, you can substitute fat-based liquids for other fat based ingredients, and water based liquids for other water based liquids.
Most breads also have the capacity to carry additional fats and sugars (called enrichment), which at its extreme leads to breads like brioche which are very sweet and fatty.
Eggs are a complex ingredient in that the whites are mostly water, with some protein (albumin), and the yolks are about 50% water and 50% fat.
See related:
Are there any general principles of ingredient substitutions? Note that in a bread recipe, with so few ingredients and a deceptively complex chemistry, all of the ingredients have a role to play in the chemistry, so the major factors you are looking at are the overall total ratios of fat, sugar, and water to the flour. Accent ingredients would be add ins like carway seeds in rye bread which don't incorporate into the dough.
In regards to your desire for more olive oil flavor, you almost certainly can substitute olive oil for any fats already in the recipe with comparable results. Most dought can even carry a little more fat, although this will inhibit yeast growth and gluten development, so that you will need more kneading and more proofing time.
You can also brush the crust with olive oil before or after baking.
The very best way to get olive oil flavor into your bread is to dip it in oil when you eat it. This also allows you to get the full flavor of a quality oil, as many nuances would be lost if it was baked into the bread.
Best Answer
I'm not familiar with how bread machines even work, so I'm not sure if you mean that you are restarting the cycle and that means that (A) you are just mixing the dough longer, or (B) the dough mixes, then rests, then mixes, then rests, etc. Either way, not a good idea.
For scenario (A), you're overworking your gluten. If you do this, it's just as bad as undermixing. You can find plenty of information on the perils of overmixing.
If it's (B), it's also not a good idea. When bread rests, you should never mechanically mix it again. You only need to 'punch it back' to expel the carbon dioxide. Mechanically mixing at this point will actually break your gluten threads. Also, adding extra yeast or sugar is just a bad idea in general. You are not going to increase any flavour, certainly not going to create a sour. For that, you need to learn how to create, maintain, and use sours / sponges.
I am not speaking flippantly here, but I would suggest reading a proper baking textbook to learn about the theory of breadmaking to enhance your knowledge and understanding of ingredients and their role...
Having said that, I'm sure someone will come along and refute everything I've said - happens here all of the time. I only speak from 20+ years of experience plus baking and pastry papers.