Fresh flour, slow bread: why we mill on stone and ferment for two days

Fresh flour, slow bread: why we mill on stone and ferment for two days

Flour is a fresh food. We mill ours whole, on stone, and give the dough two days, because that is how grain gives the most back.

Between the stones

A stone mill does one thing: it grinds the whole grain, in a single pass, and gives all of it back.

Grain drops through the eye of the top stone, the runner, which turns over a fixed bedstone. Furrows cut into both faces carry the grain outward while the flat lands between them press, shear and rub it into flour. Bran, germ and starchy endosperm are ground together, so the oils of the germ are worked right through the flour.

Stones can run hot, and heat damages oils and starch. So a careful miller turns them slowly and keeps the flour cool.

A modern roller mill works the opposite way. Steel rollers crack the grain open and sieves pull it apart into white flour, fine bran and coarse bran, with the germ carried off in the bran. White flour is what remains when those streams are left out.

Italian researchers milled the same eight lots of wheat both ways and measured what each flour held (Carcea et al., 2020).

Per 100 g dry flour

Stone-milled whole flour

Refined roller flour

Fibre

10.2–11.5 g

1.8–2.7 g

Minerals (ash)

1.77–2.10 g

0.54–0.98 g

Natural oils

1.9–3.0 g

0.7–1.7 g

Alkylresorcinols (bran compounds)

35–47 mg

None detected

A review of the published comparisons reached a similar verdict, crediting stone milling with higher levels of minerals and polyphenols in the flour.

Why fresh flour makes living bread

A grain of wheat is a seed, built to stay whole until it is time to grow. Grinding breaks that seal, and the flour starts to change from the first hour.

The germ's oils meet air and the grain's own enzymes. In stored wholemeal, an enzyme in the bran steadily splits those oils into free fatty acids over several weeks, the first step toward rancid flavour (Galliard, 1986).

Vitamin E goes with them. Studies of stored wholegrain flour report losses of 30–50% over a year at room temperature, and more than half within eight weeks at 26 °C (Food Chemistry, 2021).

This is why whole flour has a short shelf life, and why the industry built itself around white flour. Take out the germ and the bran and the flour will sit on a shelf for months.

Fresh whole flour is also active. It carries the grain's own enzymes: amylases that turn starch into sugars for fermentation, and phytase, which frees minerals once the dough turns acidic. It carries wild yeasts and lactic acid bacteria that lived on the grain.

Add water and a sourdough culture and all of it wakes up. Dough made with flour milled days ago ferments with an energy that old flour does not have. You can see it in the bowl and smell it in the room.

That is what we mean by living bread. The oven ends the fermentation, but the loaf keeps everything the microbes made: the acids, the aroma, the open crumb and a grain that has been thoroughly worked over before it reaches you.

What happens to supermarket flour

The flour on a Kenyan supermarket shelf has usually travelled for months before you open the bag. Kenya grows only about 8% of the wheat it eats. The other 92% is imported, mostly from Russia, Ukraine and the European Union, according to the Agriculture and Food Authority. In August 2026 millers put the imported share nearer 95%.

That grain makes a long trip:

  1. Harvested abroad and held in farm and export silos.
  2. Shipped in bulk across the sea to Mombasa.
  3. Stored again in port and mill silos until it is needed.
  4. Roller-milled, with the bran and germ taken out.
  5. Aged, fortified, packed and trucked to warehouses and shops.
  6. Left on the shelf, then in your cupboard.

Fumigation

Grain that sits in bulk attracts weevils and grain borers. The standard answer, in Kenya as everywhere, is fumigation with phosphine gas. Tablets of aluminium phosphide are added to the grain or laid under sealed sheets, where they react with moisture and release the gas (FAO fumigation manual). The gas is toxic enough that in Kenya only registered fumigators may use it (De Groote et al., 2013).

Phosphine airs off quickly, and international limits cap what may remain at 0.1 mg per kg of grain and 0.01 mg per kg of flour (FAO). It is legal and it works. It is also a treatment that only long storage makes necessary.

Ageing

Fresh white flour is not ready for industrial baking. Millers call it green flour: yellowish, with weak gluten.

Left exposed to air for several weeks, it oxidises. The yellow pigments fade and the gluten strengthens. Many industrial mills skip the wait with bleaching and maturing agents such as benzoyl peroxide and chlorine dioxide (Britannica). Rules differ by country, so read the label. The pigments that fade are carotenoids, part of what gives fresh flour its creamy colour and its flavour.

Adding back

Since 2012 Kenyan law has required packaged wheat flour to be fortified with iron, zinc, folic acid and other vitamins (Food Fortification Initiative). It is good public health policy. It is also an admission of how much refining removes.

Two days, no shortcuts

Our sourdough takes two days because the useful work of fermentation is slow, and no additive does it faster.

A factory loaf goes from flour to bag in a few hours, raised by a large dose of commercial yeast. Ours is raised by a sourdough culture, a community of wild yeasts and lactic acid bacteria. They work slowly, and they do far more than make gas.

They unlock minerals. Whole grain is rich in iron, zinc and magnesium, but much of it is bound to phytic acid in the bran. As the bacteria acidify the dough, the grain's own phytase switches on and breaks that bond. In whole wheat bread, sourdough cut phytate by 62%, against 38% for yeast alone, and left more magnesium in soluble form (Lopez et al., 2001).

A 2026 review of human studies found that well-fermented sourdough bread improves iron absorption from the meal for the same reason.

They break down troublesome proteins. Wheat contains amylase-trypsin inhibitors, proteins linked to wheat sensitivity. Once sourdough drops below pH 4, the grain's enzymes take them apart. In yeast dough they stay intact (Huang et al., 2020).

They are gentler on blood sugar. A pooled analysis of 18 clinical trials found lower blood glucose 60 and 120 minutes after sourdough than after industrial bread. A 2026 review found some benefit in 10 of 12 studies. Results vary from trial to trial, because sourdoughs vary. Long, properly sour fermentation is the kind that shows the effect.

They make flavour. Lactic and acetic acids, and the hundreds of aroma compounds built over a long ferment, are why this bread tastes of something and keeps for days without preservatives.

Fresh whole flour and slow fermentation belong together. Whole flour brings the minerals and the bran, and time and acidity are what make them available to you.

One caution: sourdough is not gluten-free and is not safe for people with coeliac disease.

Glyphosate: what fermentation can and cannot do

Fermentation may break down some glyphosate, but the grain you start with matters far more. Glyphosate is the world's most widely used weedkiller. In some wheat-exporting countries it is also sprayed shortly before harvest to dry the crop evenly, and that leaves residue on the grain. A Canadian survey cited in Cereal Chemistry found measurable glyphosate in 76% of 807 wheat products, all within legal limits.

You may have read that sourdough destroys it. Here is what has been measured: The hopeful study. Researchers in New Zealand added glyphosate to bread dough and found that baker's yeast broke down about 21% of it in one hour of fermentation (Low et al., 2005). This is still not completely determined but its hopeful.

    What this means for your loaf

    Our bread starts with grain ground whole on stone, used within days of milling and fermented for two days.

    Nothing is taken out of the grain. The flour goes from stone to dough before its oils and vitamins fade. And the dough gets the time it needs for fermentation to do its work.

    The simplest test is to taste it. Fresh flour smells sweet and nutty, and you will know the difference in the first slice.

    The research

    Stone milling

    Fresh flour and storage

    Imported wheat, fumigation and ageing

    Sourdough fermentation

    Glyphosate

    DELIA EDWINA STIRLING
    Posted on October 06, 2026
    DELIA EDWINA STIRLING
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