Learn how to turn cut size, fines, foreign matter and sampling into measurable mulberry root bark specs that cut disputes with suppliers and speed up incoming inspection.
Disputes over mulberry root bark (Sang Bai Pi, Mori Cortex) rarely start with identity. They start when a lot of “shreds” arrives as a mix of long strips and crumbs. They also start when a carton opens to a layer of brown fines, and nobody wrote down what “normal” looks like. Cut size and cleanliness are both measurable. Neither can be judged by eye from a photo.
This guide shows how to define each one as a specification: what to measure, how to measure it, how to sample, and what to send in an RFQ. Numeric limits shown are placeholders. Agree them with your supplier and your target-market monograph.
Bark is plant tissue with natural variation, and processing adds more. A fibrous bark frays when cut, sheds fines during handling, and settles in transit so the bottom of a carton ends up dustier than the top. The two problems are linked: a finer cut or a worn screen usually produces more fines. Specify both together.
Most disputes come from three gaps:
Fix the product form first, because every number depends on it.
The Sang Bai Pi bulk supply page describes the product as dried bark that is light brown with a tough, fibrous texture. That fibrous character is why cut quality and fines control need to be written into the spec rather than assumed.
Choose the dimension that creates a problem downstream:
| End use | Dimension most likely to cause problems | Why it matters |
|---|---|---|
| Decoction pieces | Length/width band and uniformity | Affects wetting, boil behaviour and appearance of the dispensed piece |
| Tea bags / tea-cut | Oversize pieces and fines | Long strips can jam filling lines. Fines pass through filter paper and cloud the brew |
| Extraction feedstock | Average particle size and its spread | Affects extraction consistency and packing density in the extractor |
| Powder-ready granules | Mesh window and retained % per screen | Affects milling load and the dust generated downstream |
For general reference, the site’s guide to choosing the right cut size for decoction pieces lists common bands: thin slice 1–2 mm, thick slice 2–4 mm, segments about 5–10 mm, and dice about 8–12 mm. It notes that thinner cuts raise surface area but also fines. These are general decoction-piece bands and not Sang Bai Pi-specific limits, so treat them as starting points.
One practical point: in bark shreds or strips, part of the thickness is a raw-material property (how thick the bark was when peeled). The cutter mainly controls length and width. If you spec a tight thickness band, expect the supplier to select raw material, not only adjust a blade.
A range with no method invites argument. The site’s article on defining thickness without endless disputes makes this point well: thickness is a measurement result, and it changes with gauge force, foot size and dwell time. It recommends writing down the device, force or pressure, contact size and read time. It also recommends deciding whether you want spot thickness (the thickest point, relevant to jamming) or average thickness (relevant to extraction consistency).
Apply the same logic to each dimension:
“All pieces must be 3–5 mm wide” is unrealistic for a fibrous bark. Write a rule that a supplier can pass and an inspector can audit:
That last item matters. The thickness article cites ASTM F2251 as an example of a test method that gives no pass/fail criteria, so buyer and supplier must set them. The cut-size guide suggests accepting on the average while flagging clusters of outliers.
A qualification worth making: tighter is not automatically better. Each extra rescreen to hit a narrow band generates fines and adds cost and rework. Set the tightest tolerance where size causes a real problem (a filling line, extraction or visible appearance), and keep it looser elsewhere. Premium retail packs where appearance sells are the exception.
“Clean” is four separate things measured four different ways. Spec them separately.
Define fines by a sieve test, not by looking at the bag. Pick a screen opening below your smallest acceptable piece and state a maximum percentage by weight passing through it. The WHO guideline on quality control methods for medicinal plant materials lists a sieve series by nominal aperture in micrometres (for example 250, 212 and 180 µm), and lists degree of fragmentation by sieve test among the tests on final samples.
Fines also move. The barks sampling guide notes that vibration pushes dust downward, so one carton becomes “powder-heavy.” State where in the carton the sample is taken, and test again at receipt, not only at dispatch.
The WHO guideline defines foreign matter as:
For root bark, typical items to name in your spec are attached wood, residual outer cork layer and soil. Ask the supplier which of these your target monograph allows and at what level. That list is a working inference, not a WHO list.
For method, WHO describes a visual sort under 6× or 10× magnification, and sifting the remainder through a No. 250 sieve. In that method, the dust that passes is regarded as mineral admixture. It also gives sample sizes: 500 g for roots, rhizomes and bark, and 50 g for cut material whose fragments average under 0.5 g. If you want bark fines and mineral dust reported separately, tell the lab, because that method treats them together.
The same WHO guideline says medicinal plant materials should be entirely free from visible signs of mould, insects and animal contamination. It also says there should be no abnormal odour, discoloration, slime or sign of deterioration. Treat this as a zero-tolerance visual check on every opened carton, not an averaged percentage.
Damp pockets cause clumping and mould risk. The barks sampling guide lists moisture gradients (outer layers dry faster than the middle) as a reason to open several cartons. Set the moisture limit from your target monograph or your own storage needs. Do not copy a number from another herb.
Dust that shows up in your carton was usually created at screening and packing. The site’s article on cleaning standards that reduce dust complaints argues that dust complaints are cleaning-standard issues and should be written into the spec. Its suggested clauses are:
That article focuses on powder lines, but the same questions apply to the screening and packing stations for cut bark.
Use this as a structure. Replace bracketed values with limits agreed for your product and market.
| Parameter | What to write | Suggested method | What to agree |
|---|---|---|---|
| Form and processing | Raw or honey-processed; strips, shreds or pieces | Golden sample + written description | Which monograph or standard applies |
| Length / width band | [A–B] mm | Tray and ruler, defined piece count | Min % in band by weight |
| Thickness | Spot or average, with gauge, force, foot size, read time | Contact gauge | Acceptance rule and outlier action |
| Oversize | Max [C] mm | Template or screen | Max % allowed |
| Fines | Max [Y]% passing [screen size] | Sieve test, defined sample weight | Where in the carton to sample |
| Foreign matter | Wood, residual cork, soil, other items named | Visual sort + sieve, per WHO-style method | Max % per group and total |
| Mould / insects / odour | Visible signs and abnormal odour | Visual and sensory check of every opened carton | Zero tolerance and the action taken |
| Moisture | Limit from your monograph | Lab method named in the spec | Action if the limit is exceeded |
| Packaging cleanliness | No visible dust on outer surfaces | Visual check at receipt | Liner type, carton sealing |
| Documents | COA per lot, lot number match | Document check | Retain samples, response time for complaints |
There is no single universal answer. Two published approaches give different counts:
| Cartons in lot (N) | WHO guideline sampling | √N + 1 field rule (site’s barks sampling guide) |
|---|---|---|
| 9 | 5 | 4 |
| 16 | 5 | 5 |
| 40 | 5 | 8 |
| 100 | 10 | 11 |
| 400 | 40 | 21 |
WHO’s procedure samples each container in a batch of up to five units, five containers in a batch of 6–50, and 10% (rounded up to a multiple of ten) above 50. Three original samples are taken from each container: top, middle and bottom. The √N + 1 rule is described on the site’s barks sampling plan as a field rule, not a formal standard. That page pairs it with AQL sampling (ISO 2859-1 / ANSI/ASQ Z1.4), which decides how many units to inspect. The carton rule decides how widely you spread those units.
A workable approach:
Send these items with the RFQ so the quote and the first lot match:
If you are ready to request pricing, start from the mulberry root bark (Sang Bai Pi) bulk supply page and attach your spec. The page lists a 1 kg MOQ, a 7-day lead time, and free samples and COA reports. Confirm current terms when you request a quote.
What cut size should mulberry root bark be?
It depends on end use and the standard you must meet. Define length and width bands for decoction or tea-cut, or a mesh window for powder-ready material. Add a method, a tolerance as a percentage by weight, and an oversize limit.
How do you measure fines in mulberry root bark?
Use a sieve test. State the screen opening, the sample weight and the maximum percentage by weight passing through. Specify where in the carton to sample, because fines tend to collect toward the bottom.
What counts as foreign matter in Sang Bai Pi?
WHO defines it as other plant parts, other organisms or their products, and loose mineral material such as soil, stones, sand and dust. For root bark, name attached wood, residual outer cork and soil explicitly, and agree limits with your supplier.
How many cartons should I open for incoming inspection?
There is no single rule. WHO samples all containers in lots of up to five, five containers in lots of 6–50, and about 10% above 50. The √N + 1 field rule is another option. Write the chosen rule into the PO.
Is “dust-free” a valid specification?
No. It cannot be tested. Define a maximum fines percentage by sieve test, a visual standard for outer bag and carton cleanliness, and a response process for complaints.
Should honey-processed Sang Bai Pi share a spec with raw bark?
No. Honey-processed bark is sold as a separate product and handles differently, so give it its own SKU, spec and moisture limit.
