About flour: protein percentages and more
Protein percentage is often what bakers (home and professional) focus on. Here are some quick considerations.
A short summary: simply find out from the mill (or supplier) what the flour is designed for... and bake!
Image: bread wheat growing in our backyard.
Protein
The protein content on the nutrition panel tells how much protein is in the food (e.g. flour). What it doesn't tell is what type/s of protein. For bread-making, we typically want a balance of two proteins to form gluten. The ratios and quality of these heavily influences how the dough will form and what characteristics it will have.
Bread wheats (what are grown and milled for bread-making) are on a spectrum. The same protein content percentage might make a very stretchy dough or it might make a very tight dough. Why? Because it depends on what types of proteins are in the wheat > flour.
Often wholemeal/wholegrain flours are high protein, but part of that protein is in the bran, which won't contribute to the dough structure.
In 'ancient' grains they might be high in protein but not the same proteins as bread wheat/s. So, they won't form a structure and hold gas as efficiently.
Summary: the types, ratios and quality of protein matter more than the overall quantity.
Flour mills carefully manage the technical side - analysing and selecting grain/s - so we (the bakers) get a consistent flour to bake with.
Starch
During milling the starches are damaged (because they get crushed!). In modern roller-mills (using a series of stainless steel rollers and sifters) the mill can control how much damage the starches experience. Milling is an art and science (just like baking).
During dough fermentation the yeast/s (‘wild’ sourdough or manufactured yeast) feed on the starches. Among other factors, how much the starches are damaged influences how quickly the dough ferments and how much starch (sugars) are available to contribute to browning during baking.
A flour with more damaged starch will ferment quicker (the yeast can get to them easily) vs a flour with less damaged starch will ferment slower (because the enzymes have to change the starch before the yeast can get to them).
So, for the person baking, a flour with more damaged starch will generally enable a dough to ferment quicker (great for yeasted Hot Cross Buns, for example). A flour with less damaged starch will ferment slower (great for sourdough or a long fermented yeast bread, for example).
Too much starch damage (very rough milling, for example) will cause a sticky dough that releases water during fermentation and has lots of enzyme activity, which can cause a reddish colour to the breads crust.
Not enough starch damage (less common) may mean the dough ferments slowly and doesn’t brown well during baking.
Ash
Less common here in Australia, but common in Europe is classifying flours by ash content. This is what the ‘T’ means (e.g. ‘T55 flour’ = ‘Type 55 flour’).
A small quantity of flour is weighed, incinerated and re-weighed. The minerals remain after the burning heat and their weight becomes the classification as a ratio to overall mineral content. Why burn flour? Because the minerals are usually around the outer parts of the grain, so the mineral component represents how wholegrain or refined the flour is.
Generally, a higher number means more minerals which means a more wholegrain flour. A lower number is less minerals so more refined.
T55 is a standard ‘white’ wheat bread flour.
Summary
All the classifications and technical data can be confusing; what I recommend to my students (and usually recommend to bakers, too) is simply find out from the mill (or supplier) what the flour is designed for... and bake!
A bake test, when having a an approximate idea of what the flour is for, will give the ultimate result.