Loss on drying is the weight a sample loses when it is dried under stated conditions: water, and anything else that evaporates. Ash is what remains when the sample is burned, and a sieve row gives the share of the powder that passes a named sieve. Each figure belongs to the method that produced it.
Below the assay, an extract specification often carries a short block of physical rows: loss on drying or moisture, ash, particle size, sometimes bulk density. They are easy to pass over. They bear on how the powder keeps, how it runs through your process and how much of each kilogram is water rather than extract.
Here are six checks to make on these rows. They draw on the World Health Organization’s test methods for herbal materials, on European guidance for herbal medicines, on the Japanese Pharmacopoeia, whose English edition is free to read, on an international guideline for medicines and on a United States rule for dietary supplements. Our earlier articles covered the specification, the extract ratio, the Certificate of Analysis, the solvent and carrier, the heavy metal and pesticide rows, the assay method, the microbiological rows and the identification row; this one stays with the physical rows.
01 / THE LOSS
Is the figure water, or everything that evaporates?
Loss on drying is a weighing, not a test for water. The World Health Organization’s methods for herbal materials say that the test “determines both water and volatile matter”, whereas a distillation method “gives a direct measurement of the water present in the material being examined”.1
European guidance for herbal medicines allows the simpler test, with a reservation. For an extract, it says, a loss on drying procedure “may be adequate; however, in some cases (essential oil containing preparations) an analytical procedure that is specific for water is required”.2 In its section on finished herbal medicines it gives Karl Fischer titration, a chemical test for water itself, as an example of a more specific procedure.2
So the heading of the row does not settle the question: the guidance itself deals with loss on drying under the heading “water content”.2 What settles it is the method the row names. Only a method specific for water leaves out the other matter that evaporates.
Check: whether the row reports loss on drying or water, and which method stands behind it.
02 / THE CONDITIONS
Under which conditions was the sample dried?
A loss on drying figure is tied to the way the sample was dried. The Japanese Pharmacopoeia defines the test as measuring the loss in mass of the sample “when dried under the conditions specified in each monograph”, a monograph being its entry for one substance. It writes those conditions into the limit itself: “not more than 1.0% (1 g, 105°C, 4 hours)” means that about 1 g of the substance is dried at 105°C for 4 hours.3
The World Health Organization’s procedure for herbal materials allows two routes: an oven at 100–105°C, or a desiccator, a closed vessel that holds a drying agent, at room temperature. It notes that the second “is especially useful for materials that melt to a sticky mass at elevated temperatures”.1
For herbal materials the same methods give the reason for a limit: “An excess of water in herbal materials will encourage microbial growth, the presence of fungi or insects, and deterioration following hydrolysis”, that is, breakdown by water. A limit, they add, is especially important “for materials that absorb moisture easily or deteriorate quickly in the presence of water”.1
A powder that absorbs moisture easily may not keep the figure it had on the day of the test once it is exposed to humid air, for example after its packaging has been opened. Our article on the microbiological rows explains why a moisture figure helps to judge the risk of microbial growth but cannot replace the counts.
Check: the temperature or drying agent, the time and the sample size behind the figure, or the pharmacopoeia method the row cites.
03 / THE BASIS
Is the assay a share of the dried powder, or of the powder as supplied?
Moisture also changes what the other percentages mean. A content can be stated for the powder as it is, or for its dry matter: the powder less what it lost on drying, the “dried basis”, or less its measured water, the “anhydrous basis”. The two are not the same, because loss on drying also counts other volatile matter. The Japanese Pharmacopoeia, for example, has the solvent-soluble matter of crude drugs, its term for medicinal parts of plants or animals, their extracts and minerals, calculated “on the dried basis, obtained under the loss on drying”, and for one reagent has the water determined separately and a result calculated “on the anhydrous basis”.3
The arithmetic is short and worth doing. With a loss on drying of 5.0%, for example, an assay of 20.0% on the dried basis is 19.0% of the powder as supplied. A specification that does not say which basis its assay uses leaves that difference open.
Check: whether the assay and the other percentages are stated on the dried basis or on the powder as supplied.
04 / THE ASH
What is left after burning, and where does it come from?
Ash is the residue left when a sample is burned. For plant material the World Health Organization’s methods separate what belongs to the plant from what does not: total ash includes ash “derived from the plant tissue itself” and “the residue of the extraneous matter (e.g. sand and soil) adhering to the plant surface”.1 A second test, acid-insoluble ash, boils the total ash with dilute hydrochloric acid and ignites what does not dissolve, that is, heats it strongly; it “measures the amount of silica present, especially as sand and siliceous earth”.1
These are tests written for plant material. European guidance lists total ash and, where justified, ash insoluble in hydrochloric acid among the tests for herbal substances, the plant material itself. Its own list of tests for herbal preparations, extracts among them, includes neither, although it has a preparation follow a pharmacopoeial monograph wherever one exists.2
On an extract specification the ash row therefore needs a second look. Ash is inorganic residue, whatever its origin. The Japanese Pharmacopoeia’s residue on ignition test, in which the sample is ignited in the presence of sulfuric acid, says in its own introduction that it “is usually used for determining the content of inorganic impurities in an organic substance”.3 The European Pharmacopoeia’s text for this test is headed sulphated ash and the United States Pharmacopeia’s residue on ignition; an international guideline for medicines, last revised in 2010, recommends that the three texts “can be used as interchangeable” on stated conditions.4
In an extract, minerals that came from the plant are part of the figure, and so is an inorganic carrier or flow agent where one has been added, though not necessarily at the weight that was added. A carrier that is not mineral leaves little or no ash, so a low ash figure does not show that an extract contains no carrier. The ash row and the carrier line should be read together.
Total ash, acid-insoluble ash and residue on ignition are three different procedures, so a limit means little until the row says which one it uses.
Check: which ash test the row refers to, and whether its limit allows for any inorganic carrier in the extract.
05 / THE SIEVE
What does “80 mesh” promise?
A figure such as “95% through 80 mesh” is a sieve result. The Japanese Pharmacopoeia’s chapter on particle size, which apart from marked passages is harmonised with the European and United States pharmacopoeias, calls sieving “one of the oldest methods of classifying powders and granules by particle size distribution”.3
A mesh number names a sieve; it is not a particle size. The chapter asks for sieve openings to be stated in micrometres or millimetres and says that sieve numbers “are provided in the table for conversion purposes only”. In its table the United States sieve No. 80 has an opening of 180 µm, No. 100 one of 150 µm and No. 200 one of 75 µm, while the Japanese number for the 180 µm sieve is 83.3 In the World Health Organization’s methods a “No. 180 sieve” is simply a sieve with an opening of 180 µm.1 A specification does not always say which series its “80 mesh” belongs to; the opening in micrometres settles it.
The sieve is half of the result; the share that passes it is the other half. The World Health Organization’s classes show both: a “fine” powder is one of which “all the particles will pass through a No. 180 sieve”, and a “moderately fine” one passes a No. 355 sieve with “not more than 40% through a No. 180 sieve”.1
How the sieving was done matters too. The chapter’s analytical sieving method “is intended for estimation of the total particle size distribution of a single material” and “is not intended for determination of the proportion of particles passing or retained on one or two sieves”. Where only the share above or below one sieve is wanted, it describes air jet sieving, which uses a single sieve at a time, as “more suitable where only oversize or undersize fractions are needed”.3
European guidance asks for particle size to be considered for extracts used in herbal medicines, because in a medicine it “can have a significant effect on disintegration time, dissolution rate, bioavailability, and/or stability”.2 The sieving chapter adds a caution that links this row to the first one: a material “prone to picking up or losing significant amounts of water with varying humidity” has to be tested in a controlled environment.3
Check: the sieve, by its opening in micrometres as well as its mesh number, the percentage that passes it and how the sieving was done.
06 / THE DENSITY
Untapped or tapped, and measured how?
Bulk density says how much a given volume of powder weighs, the gaps between its particles included. The Japanese Pharmacopoeia’s chapter on it, harmonised in the same way, defines bulk density as “the ratio of the mass of a powder sample to its volume, including the contribution of the interparticulate void volume”.3
It is not a fixed property of the material. “The bulk properties of a powder are dependent upon the preparation, treatment and storage of the sample, i.e. how it has been handled”, the chapter says. For cohesive powders in particular, those whose particles cling together, the untapped figure “is often very difficult to measure with good reproducibility”, and in reporting the results “it is essential to specify how the determination was made”.3
The tapped figure is “an increased bulk density attained after mechanically tapping a receptacle containing the powder sample”, and the two together “are used to evaluate powder flow”.3 A single density figure that does not say whether it is untapped or tapped, or how it was measured, cannot safely be compared with a figure from another source.
A last point concerns all of these rows. None of them is named in the United States rule on specifications for dietary supplements, which requires the company that makes a supplement to establish the component specifications “that are necessary to ensure that specifications for the purity, strength and composition of dietary supplements manufactured using the components are met”.5 Under that rule it is for the maker of the supplement to decide which physical rows are necessary. Wherever you sell, the rows your product and your process depend on are yours to state.
Check: whether the density is untapped or tapped, the method used to measure it, and which of the physical rows your own specification needs.
WHAT TO SEND
State your physical requirements with your enquiry
When the physical rows matter to your product or your process, tell us:
- the ingredient, and the plant part if more than one is offered;
- your intended application and destination market;
- the limit your quality team sets for loss on drying or water, and the method it uses;
- whether your assay figures are calculated on the dried basis or on the powder as supplied;
- the sieve and the percentage passing that your process needs, and a bulk density range if your equipment needs one;
- whether you will test the delivery yourself, and by which method;
- which technical documents you need, such as a specification sheet or Certificate of Analysis;
- your name, company and contact details.
We offer technical documentation and COA support, and the available document set is confirmed for each ingredient and project. Specification ranges in our catalogue are references, and feasibility, availability and price are confirmed with your quotation.
This article describes published test methods, published guidance and law and gives no loss on drying, ash, particle size or density values for YOHOLIFE® ingredients; the specification and documents for a selected grade are confirmed when you enquire. Source 1 was written for herbal materials and source 2 for herbal medicines; both are cited here for their definitions and approach. Source 3 is a pharmacopoeia written for medicines and is cited for its definitions; its chapters on particle size and bulk density state that, apart from passages marked as Japanese text, they are harmonised with the European Pharmacopoeia and the United States Pharmacopeia, which are not quoted here. Source 4 is an international guideline for medicines. Source 5 is United States law. Food law in the European Union and Great Britain is not covered here. Sources were checked on 13 November 2026 and are given for orientation, not as regulatory advice.
