On a dry kibble label, some expressions seem more alarming than others. "Crude ash" often comes at the top of the list.
The word spontaneously evokes fireplace residue or a worthless ingredient. Yet, it simply describes a laboratory measurement. As with proteins, carbohydrates, or fats, the number only becomes useful when you understand what it measures and put it into the context of the full formulation.
🔥 "Crude ash": what are we really talking about?
The expressions "crude ash," "mineral matter," or sometimes just "ash" refer to the total mineral fraction of the food as measured by an analytical method.
Obviously, this is not about ash added to the kibble. The manufacturer does not pour burnt wood or fireplace residue into the recipe. The term comes from the way the laboratory measures this fraction.
Minerals are naturally present in raw materials and can also be added in a controlled manner to balance the food. Meats, fish, bones or mineralized tissues, cereals, legumes, and mineral supplements all contribute, in varying proportions, to the final result.
🧪 How is this value obtained?
To measure crude ash, the laboratory takes a known quantity of food and then heats it to a very high temperature under controlled conditions.
The organic matter—proteins, lipids, and carbohydrates in particular—is destroyed by combustion. What remains is an inorganic residue composed mainly of minerals. This residue is weighed and related to the amount of food analyzed.
If a kibble displays 8% crude ash, it means that about 8 g of mineral residue was measured per 100 g of food as sold, unless another calculation base is indicated.
👉 The word "crude" here describes a global analytical method. It means neither "dirty," nor "unrefined," nor "poor quality."
🪨 Which minerals are hidden behind this figure?
The total value can include:
- calcium;
- phosphorus;
- potassium;
- sodium;
- magnesium;
- trace elements like iron, zinc, copper, manganese, iodine, or selenium.
This list already shows the main limitation of the ash content: it adds up very different elements without indicating the quantity of each, their origin, their bioavailability for the organism, or their balance.
Two kibbles with 8% ash can therefore have very different levels of calcium, phosphorus, sodium, or trace elements.
📊 Does a high rate mean a lot of bone or mediocre ingredients?
Not necessarily.
Some raw materials rich in mineralized tissues can increase the mineral fraction. But the total rate alone does not make it possible to identify the responsible ingredients or to evaluate their quality.
A recipe can also contain more minerals because it is formulated to meet precise nutritional needs. Conversely, a low rate proves neither a better selection of raw materials nor a better nutritional balance.
It is the same caution as in our guide to reading the composition of kibble: an analytical constituent provides quantitative information, but it never tells the whole recipe.
⚖️ Why the percentage alone does not allow you to judge a kibble
The ash content depends on the entire formulation. It must be compared with:
- individual mineral levels when available;
- the life stage for which the food is intended;
- its energy density and the quantity actually consumed;
- the comparison base used, particularly food as sold vs. dry matter;
- the dog's specific needs.
Comparing 7% and 9% without this information is like comparing two totals where the details are unknown.
A relatively high rate is therefore not automatically excessive. A relatively low rate is not automatically ideal. And setting a rule like "above X%, kibble is bad" precisely erases the information you would need to make a judgment.
Beware of the comparison base
Water dilutes percentages. Two foods with different moisture levels cannot always be compared directly. For kibbles with similar moisture, the difference is often limited, but if you want to be rigorous, you can compare on dry matter:
Ash on dry matter = stated rate ÷ (100 − moisture) × 100
At 8% ash and 10% moisture, you get about 8.9% on dry matter. This calculation harmonizes the basis of comparison; it still does not turn the total into a quality verdict.
🦴 Calcium and phosphorus: look at the quantities and the balance
Calcium and phosphorus contribute notably to the structure of bones and teeth, but also to many cellular functions. Their value cannot be summarized as just "a lot" or "a little."
You must examine their individual levels and their balance. A food may have an apparently reasonable total ash content while providing no information on the distribution between these two minerals.
The calcium/phosphorus ratio therefore provides useful context, but it too should not be read in isolation: consistent proportions do not necessarily compensate for unsuitable total quantities.
During growth, caution is particularly important
In puppies, the skeleton develops rapidly. Calcium and phosphorus intakes must be controlled and adapted to the growth stage. Large-breed puppies require particular vigilance because growth that is too rapid or mineral intakes that are unbalanced can harm bone development.
The right approach is not to arbitrarily choose the kibble with the least ash. It is to verify that the food is complete and formulated for the specific growth stage, then to examine the calcium and phosphorus levels provided by the manufacturer. If in doubt, especially for a large-breed puppy or an animal with a health problem, the choice should be discussed with a veterinarian.
Furthermore, a complete food does not need to be supplemented with calcium "just in case" without professional advice: an addition can unbalance a formula that was balanced to begin with.
🐾 Lower is not necessarily better
Systematically looking for the lowest ash rate seems simple, but this shortcut can distract from more useful questions:
- does the food cover the dog's needs for its age and lifestyle?
- are calcium and phosphorus levels available?
- does the manufacturer disclose other important minerals?
- are the data expressed on the same basis?
- is the distributed ration adapted to the energy density of the food?
- does the dog maintain a satisfactory weight, silhouette, and digestive tolerance?
The formulation works as a whole. If the share of one fraction decreases, the relative place of the others increases. As we saw with the carbohydrate calculation, changing one figure changes the reading of the rest of the recipe without, on its own, providing a qualitative ranking.
🐺 The Sköll & Hati perspective
To compare the mineral information of two kibbles, I follow five simple steps:
1. I compare foods intended for the same profile.
Puppy, adult, senior, small or large breed: I first verify that both recipes correspond to the dog's life stage and needs.
2. I check the ash rate and moisture.
I make sure the values are expressed on the same basis. If the moisture differs significantly, I compare on dry matter.
3. I look for the details rather than just the total.
I look for at least calcium and phosphorus, then their ratio if it is disclosed. I also note the sodium, potassium, magnesium, and available trace elements.
4. I treat absences as unknowns.
A value not displayed does not equal zero. I ask the manufacturer for it, along with the calculation basis and, if possible, the complete nutritional analysis.
5. I return to the complete food and my dog.
I do not decide between two kibbles based on one percentage point of ash. I look at the overall formulation, the energy per ration, the life stage, the body condition, and the dog's actual tolerance.
👉 If the ash rates differ but one of the manufacturers clearly provides the mineral levels and the nutritional adequacy of their food, this transparency is often more useful than a total that is simply lower.
Key takeaways
- Crude ash is not an added ingredient: it corresponds to the mineral residue obtained after controlled combustion of the food in a laboratory.
- It groups together calcium, phosphorus, potassium, sodium, magnesium, and trace elements.
- The total percentage specifies neither the distribution of minerals, nor their balance, nor the overall quality of the kibble.
- A higher or lower rate must always be interpreted in the context of the complete formulation.
- Calcium, phosphorus, and their balance deserve special attention during growth.
- The best reflex is to examine the available mineral levels and the suitability of the food for the dog, not to arbitrarily seek the lowest ash rate.