What is Ash Content in Flour? Classification & Impact on Dough
Ash content is a technical specification used by millers to classify flour based on its degree of refinement. By measuring the mineral-rich bran remaining after the milling process, ash content provides a blueprint of the flour’s ‘purity’. This article explores the science of ash measurement, how it dictates European flour standards, and its tangible effects on dough fermentation and structure
Introduction: Defining Ash and the Milling Process
The wheat kernel consists of three parts: the endosperm, bran, and germ. The endosperm, which contains all the gluten-forming proteins, makes up the majority of the wheat kernel. What we refer to as “white flour” is essentially just the endosperm, separated from the bran and germ.
On the other hand, wholemeal flour is made from the entire wheat kernel and includes both the bran and germ. The more bran a flour contains, the closer it is to being considered “whole wheat”.
For further reading on flour in general, refer to the following article: Guide to Understanding Flour – Types, Role in Baking, Characteristics, and Essential Knowledge.
The ash content is the tool used to measure the amount of bran that remains in the flour. Typically, the ash content in flour ranges from 0.35% to 2%.
Technical Indicators: Minerals, Bran, and Purity
The ash content in flour is technically an indicator of its mineral content. To determine the ash content, a sample of flour is burned at a high temperature. Only the minerals ‘survive’ this process, so the resulting “ash” represents the mineral content of the flour sample.
The ash obtained after burning is then weighed in relation to the weight of the original flour sample, which gives the ash content of the flour. For example, if the original flour sample weighed 100 grams and the resulting ash weighed 0.5 grams, the ash content of the flour would be 0.5% (0.005 = 100 / 0.5).
Most of the minerals in flour are found in the bran; Therefore, the ash content provides insight into the amount of bran remaining in the flour after milling, or in other words, how “pure” the flour is and how effectively the bran has been separated from the endosperm.
The lower the ash content, the more “refined” the flour is, indicating that it contains less bran (and also contains fewer nutrients, as the bran and germ hold most of the wheat kernel’s nutrients).
To conclude: Higher ash content = Higher mineral content = Flour that contains more bran (and usually germ as well).
Flour with a higher ash content will be darker (see photo above), which will result in a darker color for the baked product. A higher ash content can also affect the texture, flavor, and nutritional values of the baked product due to the increased presence of bran (and sometimes germ).
Additionally, the water absorption capacity of flour increases with higher ash content, due to the higher presence of bran.
In the past, the ash content in flour was used as an indicator of its quality (a lower bran content was considered a sign of higher quality, as it suggested better separation between the endosperm and bran).
However, as bakers today, the ash content is not significant to us and is merely a technical measurement that primarily concerns flour mills for quality control and regulatory compliance purposes.
Standards: How Ash Content Dictates Flour Classification
All European flours are primarily classified based on their ash content. Below is the classification of Italian, French, German, and American flours. For additional European flour standards, see this presentation.
| Flour Type | Ash Content |
| Italian | |
| 00 | 0.55% or lower |
| 0 | 0.55-0.65% |
| 1 | 0.65-0.80% |
| 2 | 0.80-0.95% |
| Integrale (Whole Wheat) | 1.3-1.7% |
| French | |
| T45 | 0.45% or lower |
| T55 | 0.45-0.60% |
| T65 | 0.60-0.75% |
| T80 | 0.75-0.90% |
| T110 | 1-1.2% |
| T150 (Whole Wheat) | 1.40% or higher |
| German | |
| 405 | 0.5% or lower |
| 550 | 0.50-0.63% |
| 812 | 0.63-0.90% |
| 1050 | 0.90-1.2% |
| 1600 (Whole Wheat) | 1.2-1.8% |
| American | |
| Short Patent Flour | 0.35-0.45% |
| Medium Patent Flour | 0.45-0.55% |
| Long Patent Flour | 0.55-0.65% |
| Straight Flour | 0.6-0.7% |
| First Clear Flour | 0.8-1% |
| Second Clear Flour | 1% or higher |
| Whole Wheat Flour | 1.5-2% |
It is important to note that the classification of flours above is based solely on their ash content. Aside from meeting the specified ash content range, these flours can possess a wide range of characteristics.
For instance, Italian “00” flours can vary in protein content (and other characteristics), ranging from 9% to 14%; The only information conveyed by “00” flour is simply that it contains an ash content of 0.55% or less.
The same applies to all other types of European flours, be it German, French, or Italian (for specific classification of other European countries, refer to the presentation linked above).
Fermentation: Minerals as Yeast and Bacterial Nutrients
The mineral content indicated by ash levels also influences fermentation activity.
Generally, higher ash flours provide more minerals that act as nutrients for yeast and bacteria during fermentation. These minerals, particularly magnesium and iron, help activate enzymes essential for yeast and lactic acid bacteria metabolism, potentially leading to more vigorous fermentation.
However, this effect is relatively minor compared to other factors affecting the rate of fermentation.
Structural Impact: Bran Particles and Gluten Integrity
Higher ash content flour contains more bran particles that interfere with gluten development.
These bran particles act like tiny blades, physically cutting through developing gluten strands. This leads to a tighter, less open crumb structure in the final product. The higher the ash content, the more significant the impact on crumb structure.
This is why wholemeal flours generally produce denser crumbs compared to white flour.
For pizza making, lower ash content flours (like 00) are often preferred because they support optimal gluten development with minimal interference from bran.
Key Takeaways
- The Core Definition:
Ash content is a measurement of the minerals (like magnesium and iron) present in flour. It is determined by burning a flour sample at high temperatures; the non-combustible material left behind is the “ash.” - Refinement Indicator:
Since minerals are concentrated in the bran, ash content indicates how much bran remains in the flour. A lower ash content (e.g., 0.5%) means the flour is highly refined and consists mostly of the white endosperm. - Classification vs. Strength:
European flours (Italian, French, German) are classified primarily by their ash content. Crucially, labels like “00 flour” or “Type 45” only indicate ash levels – they do not indicate protein quality or strength (W rating), which can vary wildly within the same classification. - Impact on Structure:
Higher ash content indicates more bran particles. These particles interfere with gluten development and act like tiny blades that physically cut gluten strands, leading to a tighter, denser crumb and reduced volume & dough strength compared to low-ash flours. - Water Absorption:
Higher ash content (more bran) increases the flour’s water absorption capacity, as bran is highly hydrophilic compared to the endosperm. - Fermentation Effects:
Minerals act as nutrients for yeast and lactic acid bacteria. Flour with higher ash content can lead to slightly more vigorous fermentation. - Flavor & Texture:
High-ash flours result in a darker crust color, a more pronounced “wheaty” flavor, and higher nutritional value due to the presence of the bran and germ.
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