What is the minimum ingredient to bake a bread?

The minimum ingredients to make ("western") tasting bread are:

• Flour
• Water

You would also need, albeit they are not considered ingredients:

• Time
• Air (*)
• A source of heat (usually an oven, but can also be a pot (such a Dutch oven), or some weirder for non so "western" breads).

When you give time to your mix of water and flour, you will get a culture of yeasts and bacteria. That culture has different names by different people: levain, starter, sourdough, biga...

It is important to note most of these yeasts and bacteria come with the flour, and they can perfectly rise your bread.

It wasn't until the identification of yeasts with microscopes in 1800s, when Saccharomyces cerevisiae yeast was taken apart from beer maker's cultures, and grown specifically. Beer makers also fed their cultures with just flour and water. When you add a packet or a cube of yeast to make your bread dough, you are adding a culture of yeasts selected to enhance the grown of the dough.

I marked Air with an (*) because I'm not sure it is really essential. It can give some yeasts and bacterias to the culture, but flour has enough of them initially. And yeasts can grow and reproduce in 2 ways: aerobically and anaerobically. That is: with or without air. I've seen pictures of doughs grown in vacuum, but I'm not 100% sure if you could do all the process of starting your culture and rise the dough with absolutely no air at all.

To conclude: you only need water and flour (whether wheat or rye) to make a traditional loaf of bread. It might taste strange to most people today as it has no salt. But salt wasn't added to bread until 200 years ago (or so).

Specifically, you do not need for making bread:

• Salt:

Salt began to be used in bread less than 2 centuries ago. It began to be used not to give [salty] taste to the bread, but to make the dough easier to handle; due to its hygrostatic properties it makes the dough stiffer. Nowadays several traditional bread are made with no salt at all, like Mallorca (Spain) or Toscana (Italy) bread. And they are bread people eat every day. See this answer on reducing amount of salt in bread, although I don't agree with him on taste. I think reducing salt brings up cereal flavours that were hidden. I guess it depends on the flour you use.

• Sugar/honey/malt

Saccharomyces cerevisiae yeasts eat sugar. In fact that's what "Saccharomycea" means: "sugar eater". Flour has enzymes that decompose starches in glucose, but it needs time to do so. If you add a lot of commercial yeast, it might not have enough sugar to work. So some recipes add sugar to allow yeast to have plenty of food. Malt are enzymes, so the time it takes to break down starch in glucose gets reduced. See What is the purpose of sugar in making bread and Making malt free bread

• Commercial yeast

You can have enough rising power with just levain/starter/sourdough. See What is a culture in bread

Are you trying to make sourdough bread? If not, you obviously don't need sourdough starter.

The most basic (Western) bread would just be flour, yeast, and water. You can use all-purpose flour instead of bread flour (though there are differences). Most people generally wouldn't think it tastes good without a bit of salt, and sugar is common for pretty much the same reason. But you could leave them out and still make bread.

But if you're not experienced with breadmaking, I would recommend following recipes exactly. (Ideally, you might even get a bread cookbook, but the internet will work fine too.) If you don't want to make sourdough, find a recipe that's not sourdough, rather than trying to modify this one.

The best way to think of it is in Baker's percentage.

If you have a recipe which uses for example

• 500g of bread flour

• 5g of yeast

• 2g of salt with 150ml of warm water

  the converted percentages are as follows:

• Bread is always 100%

• so the yeast would be 1% (500/5 = 0.01 = 1%)

• and 2g of salt is roughly 0.5% (500/2 = 0.005 = 0.5%)

By using this method you can bake for any quantity.

If you had to make 10 loaves of the above recipe then as long as you have the percentages correct your loaves will be great. Likewise if you wanted to reduce the flour quantity to 100g then by keeping the percentages as the same the loaf will taste the same but smaller.

You don't need the sugar. Bread is very bland without the salt, however. And you don't need both a starter and the yeast. One or the other will do.

Another note, 110F for the water is unnecessarily warm. 80-90 is better.

If you are looking for an 'unleavened' bread you can even reduce it further to something like a tortilla, with flour, salt, lard & water. It isn't a 'loaf' but it is a 'bread'.

Alton Brown offers a recipe for both flour tortillas and corn tortillas that each have a very short ingredient list.