Last reviewed: August 30, 2026. Educational content for adults 21+. This is not medical or legal advice. Kiody does not sell concentrated 7-OH products.
Suggested page: Learning Center → Lab Testing & Product Quality
The short answer
Water activity and moisture content answer different questions.
Moisture content estimates how much water is present in a sample under a defined test method.
Water activity, written as aw, measures the energy status or availability of water in a material. In formal terms, it compares the vapor pressure of water above the sample at equilibrium with the vapor pressure above pure water at the same temperature. The scale runs from 0 to 1.0.
Two powders can have similar moisture content but different water activity. The reverse can also occur. A single number cannot be converted reliably from one measure to the other unless the specific material’s moisture-sorption relationship has been established under defined conditions.
For a kratom COA, that means:
- “Moisture: 8%” is not the same result as “Water activity: 0.45.”
- A low water-activity result does not prove that Salmonella, mold, yeast, heavy metals, pesticides or other contaminants are absent.
- A microbiological “pass” does not establish that the package will remain dry after opening.
- A result from one sample does not describe every part of a heterogeneous bulk lot with certainty.
- The test date, method, sample identity, temperature and lot match matter.
The useful question is not “Is this number good?” It is “What exactly was measured, on which sample, by what method, under what conditions, and what decision was the result intended to support?”
What is water activity?
FDA defines water activity as the ratio of the vapor pressure of water in a material to the vapor pressure of pure water at the same temperature. A result of 0.80 means that the sample’s equilibrium vapor pressure is 80% of the vapor pressure above pure water under the same conditions. Water activity can also be related to equilibrium relative humidity: aw multiplied by 100 equals equilibrium relative humidity as a percentage. FDA Water Activity Inspection Guide
Water molecules in a plant powder do not all behave the same way. Some are held tightly by proteins, carbohydrates, fibers, salts and other components. Other water is more available to participate in chemical reactions, move between the product and the package headspace, or support microbial growth.
That is why aw is often described as a measure of “available” or “free” moisture. Those phrases are useful shorthand, but aw is not a physical count of loose water molecules. It is a thermodynamic measurement based on equilibrium vapor pressure.
The water-activity scale
- 0.00 represents the theoretical dry end of the scale.
- 1.00 represents pure water under the same temperature conditions.
- Values between them describe the sample’s equilibrium relationship with water vapor.
USDA’s Agricultural Research Service notes that foods may range from about 0.2 for very dry materials to about 0.99 for moist fresh materials, and that water activity is commonly measured through equilibrium relative humidity. These examples help explain the scale but are not kratom specifications. USDA ARS Water Activity in Food
What is moisture content?
Moisture content estimates the proportion of a sample attributed to water or to material lost under a specified procedure. It is commonly reported as a percentage.
The method matters. A laboratory may use:
- drying in an oven and measuring mass loss;
- a moisture balance that heats a smaller sample while weighing it;
- Karl Fischer titration, which is designed to measure water chemically; or
- another validated or compendial method suitable for the matrix.
“Loss on drying” and “water content” should not automatically be treated as synonyms. A heat-based mass-loss method can sometimes remove volatile compounds in addition to water or fail to remove all tightly associated water. Karl Fischer and oven-loss methods may therefore produce different results on the same botanical sample.
A useful COA should identify the test as moisture, loss on drying, water content or water activity and provide a method reference. A bare percentage labeled “Moisture” without a method gives less context for comparison.
Water activity versus moisture content
| Question | Water activity | Moisture content |
|---|---|---|
| What does it describe? | Water’s availability or energy status at equilibrium | Amount of water or method-defined mass loss |
| Typical format | Decimal from 0 to 1.0 | Percentage by mass |
| Does temperature matter? | Yes, directly | Yes, through method and sample handling |
| Can it help evaluate microbial growth potential? | Yes, when interpreted with matrix-specific data | Indirectly; not by itself |
| Can it be converted from the other result? | Not reliably without a product-specific sorption relationship | Not reliably without a product-specific sorption relationship |
| Does a low result prove no pathogens are present? | No | No |
| Can packaging and humidity change it? | Yes | Yes |
USDA specifically cautions that moisture content and water activity are not the same. Foods with the same moisture content may have different water activities because their components bind water differently. USDA ARS Water Activity in Food
For kratom, the binding relationship can vary with particle size, plant composition, drying history, environmental humidity, temperature and other lot-specific characteristics. A universal conversion table for every kratom powder would therefore be misleading unless supported by a defined dataset.
Why water activity matters for botanical powder
Water activity can help a quality team understand whether a dried product is likely to support microbial growth under defined conditions. FDA’s current human-food CGMP regulation defines a safe-moisture level as one low enough to prevent growth of undesirable microorganisms under intended manufacturing, processing, packing and holding conditions. The regulation links that concept to water activity and says an aw is considered safe for a food when adequate data demonstrate that the food at or below that value will not support growth of undesirable microorganisms. 21 CFR Part 117
That language contains two important limits:
- A number needs supporting data for the actual material and intended conditions.
- “Will not support growth” is not the same as “contains no microorganisms.”
A botanical powder may arrive with low aw yet already contain viable organisms. Low water activity may prevent or slow growth, but some pathogens can survive drying and remain present for long periods.
FDA’s biological-hazard sampling program states that some Salmonella can survive drying particularly well and may be difficult to kill when dehydrated or present in low-moisture products. FDA’s Salmonella laboratory chapter separately treats foods at aw ≤ 0.85 as low-moisture foods for part of its analytical workflow. FDA Sampling for Foodborne Biological Hazards, FDA BAM Chapter 5: Salmonella
The correct conclusion is:
Low water activity can limit growth under appropriate conditions, but it is not a pathogen-destruction step and it does not replace microbiological testing or process controls.
Why “below 0.85” is not a universal kratom pass limit
The number 0.85 appears frequently in food regulations and guidance. FDA uses it as a definitional boundary in certain rules for acidified and low-acid canned foods, and FDA’s current Salmonella method describes low-moisture foods as having water activity at or below 0.85.
That does not automatically make 0.85 a complete kratom specification.
First, those food rules were written for defined regulatory categories, not as product approval criteria for kratom. Second, some molds and specialized yeasts can grow at lower water activities than many bacteria. Third, prevention of growth does not mean elimination of preexisting contamination. Fourth, quality concerns such as caking, flow, packaging performance, chemical change and sensory deterioration may require tighter internal limits than a broad regulatory definition.
FDA’s water-activity guide notes that many bacteria, yeasts and molds grow readily at high water activity and that reducing available moisture can inhibit organisms. The same guide explains that aw depends on the sample’s sorption behavior and temperature. FDA Water Activity Inspection Guide
Kiody should not publish a universal kratom “pass” threshold until a qualified person has reviewed:
- product form and intended storage;
- packaging barrier properties;
- relevant microbial hazards;
- supplier and lot history;
- test method and measurement uncertainty;
- stability or moisture-ingress data;
- applicable state requirements; and
- corrective-action criteria.
Low water activity does not replace a microbial panel
Water-activity testing and microbial testing answer different questions.
Water activity asks
- How available is water in this sample at equilibrium?
- Could the environment support growth of certain organisms under defined conditions?
- Has the material gained moisture relative to its internal specification?
Microbial testing asks
- Was a specified organism detected in the tested analytical portion?
- How many culturable organisms were measured under the method conditions?
- Did the tested portion meet a defined microbiological specification?
Neither result makes the other unnecessary.
A low-aw powder can contain dormant or surviving microorganisms. A microbial result below a reporting threshold does not guarantee that another part of the lot is identical. Representative sampling, sanitary handling, validated methods and lot-level review still matter.
This distinction is especially important for Salmonella. Kiody’s water-activity page should link directly to the microbial-testing guide rather than implying that dryness is a substitute for a pathogen test.
Water activity does not replace yeast-and-mold testing
Yeasts and molds differ in their moisture requirements. FDA’s BAM material notes that molds can grow over a broad range and that some species can grow at water activity of 0.85 or less. Specialized organisms may tolerate even drier conditions. FDA BAM: Yeasts, Molds and Mycotoxins
A water-activity result can inform risk assessment, but it does not identify which organisms are present. Conversely, a yeast-and-mold count is a snapshot of the tested portion under the selected culture method and does not prove future package stability if moisture later enters.
It is also important to separate mold counts from mycotoxin testing. A low mold count does not prove that aflatoxins or other mycotoxins are absent, and a water-activity result does not measure mycotoxins at all.
Packaging can change the result over time
Botanical powder can exchange moisture with surrounding air. If the package barrier is weak, the seal is incomplete or the pouch is opened repeatedly in a humid environment, the product may absorb water. In a very dry environment, it may lose water.
The direction of moisture movement depends on the relationship between:
- product water activity;
- surrounding relative humidity;
- temperature;
- packaging permeability;
- headspace;
- seal quality; and
- time.
At equilibrium, a product with an aw of 0.50 corresponds conceptually to an equilibrium relative humidity near 50% at the same temperature. That does not mean leaving it in a 50% relative-humidity room instantly preserves the original state. Reaching equilibrium takes time, and local conditions can vary within the package.
Packaging questions for Kiody
- Is the material suitable for a moisture-sensitive powder?
- Has seal performance been checked for the chosen pouch or bottle?
- Does the closure remain functional after normal customer opening?
- Is the product packaged in a controlled-humidity environment?
- Are desiccants used, and if so, are their capacity, food-contact suitability and placement justified?
- Is a desiccant clearly separated from the product and labeled “do not eat” where appropriate?
- Has the product been evaluated through its proposed storage period?
- Are powder and capsule packages assessed separately?
The statement “resealable pouch” describes a feature; it does not prove a defined moisture-vapor transmission rate or shelf life.
Why powder and capsules may need separate review
Pure-leaf capsules contain botanical powder, but the finished product is a new matrix and package configuration.
Capsule shells can interact with environmental moisture. Too much or too little moisture may affect shell texture, brittleness, deformation or sticking depending on the shell material. The finished bottle’s headspace, closure, liner and desiccant configuration can differ substantially from a bulk powder pouch.
A water-activity result for incoming leaf powder may support receiving review, while a finished-capsule result may support packaging and stability evaluation. Those are related but not interchangeable records.
Kiody’s capsule language should remain factual: pure botanical leaf powder, approximately 500 mg fill per capsule where verified. Water-activity data should never be turned into a serving recommendation or an effect claim.
How a laboratory measures water activity
Modern laboratories commonly place a representative portion of the sample in a sealed measurement chamber. The instrument allows the sample and headspace to approach equilibrium, measures humidity or dew point and calculates water activity at a controlled temperature.
A useful report should identify:
- the method or instrument procedure;
- sample matrix;
- test temperature or temperature-control condition;
- result;
- units or aw notation;
- measurement date;
- lot or sample identifier; and
- any qualification, uncertainty or method limitation relevant to the decision.
FDA emphasizes that water activity rises with temperature and defines the measurement using sample and pure-water vapor pressures under identical conditions. Comparing results produced at different temperatures without explanation may therefore mislead. FDA Water Activity Inspection Guide
Calibration and verification questions
A quality reviewer should be able to ask:
- Was the instrument within calibration?
- Were verification standards appropriate for the expected range?
- Were sample cups clean and suitable?
- Was enough equilibration time allowed?
- Was the sample exposed to room air before testing?
- Were replicate results required?
- What happens if duplicates disagree?
A COA may not show every bench detail, but the laboratory should retain controlled procedures and records.
How moisture content may be measured
Moisture methods can differ more than a single percentage suggests.
Oven loss on drying
The sample is weighed, heated under specified conditions, cooled as required and reweighed. Mass loss is calculated as a percentage. The temperature, duration, sample amount and endpoint all matter.
Halogen or infrared moisture balance
The instrument heats and weighs a smaller sample continuously. It can be fast, but the program must be appropriate for the matrix and correlated with a suitable reference method.
Karl Fischer titration
This chemical method is designed to measure water. Sample preparation and extraction are important for plant powders, and the result can differ from heat-based loss on drying because the methods define the measurand differently.
The laboratory should not compare results from different methods as though they are identical without demonstrating equivalence or explaining the difference.
Sampling can dominate the uncertainty
A highly precise instrument cannot repair an unrepresentative sample.
Bulk botanical powder can vary by location within a sack, drum or blending vessel. Moisture can migrate or concentrate near a liner, seam, surface or area exposed during handling. A small scoop from the top may not represent the lot.
A defensible sampling plan should address:
- lot definition;
- number and location of increments;
- composite or individual-sample design;
- clean sampling tools;
- exposure time during sampling;
- moisture-barrier sample containers;
- chain of custody;
- storage before analysis; and
- reserve-sample handling.
Leaving a sample open on a bench can change the very property being measured. The sample container should minimize moisture exchange, and the laboratory should know when and how the sample was collected.
How to read a water-activity result on a COA
Use this checklist:
- Confirm the lot. The COA identifier should match the product or supplier lot.
- Confirm the matrix. Powder, whole leaf, capsules and extracts are not interchangeable.
- Find the method. Look for a water-activity method, not just “moisture.”
- Check the result format. Water activity is a decimal, not a percentage of product weight.
- Check temperature context. The result should come from controlled conditions.
- Find the specification. If “Pass” appears, the report should identify or link to the criterion used.
- Separate internal specification from law. A vendor limit is not automatically a federal or state kratom standard.
- Review related tests. Water activity does not replace Salmonella, yeast-and-mold or contaminant testing.
- Look for sample dates. Receiving, testing, packaging and report dates should form a plausible sequence.
- Check finished-product relevance. A supplier result may not represent later repackaging or capsule filling.
Example interpretation
Suppose a COA reports:
Water activity: 0.42 aw at 25 °C — Specification: ≤0.60 — Pass
The result supports only a limited statement: the tested portion measured 0.42 under the stated method and temperature and met the laboratory or client criterion shown.
It does not establish that:
- all packages in the lot are exactly 0.42;
- Salmonella is absent;
- no mold spores are present;
- the package will remain at 0.42 through its entire storage period;
- the ≤0.60 criterion is legally required nationwide;
- the product is FDA approved; or
- the product is safe for every person.
That is the difference between reading a number and overstating it.
Common water-activity and moisture red flags
- Moisture percentage labeled as aw.
- A water-activity number reported above 1.0 without explanation.
- No sample or lot identifier.
- No method reference.
- “Pass” with no specification.
- Different units on the product page and COA.
- A supplier result reused for unrelated finished-product lots.
- A generic COA that predates the received material.
- A water-activity result used to claim “pathogen free.”
- One result treated as a shelf-life study.
- Results from different test temperatures compared without context.
- “Dry” or “low moisture” used as a substitute for microbial controls.
- A compromised package accepted because the original COA passed.
What to do when a result is high or unexpected
An unexpected result should trigger a controlled review, not an automatic attempt to blend it away or dry it without investigation.
Potential review steps include:
- Place the affected lot on hold.
- Confirm the sample and lot identity.
- Review instrument verification and method conditions.
- Examine duplicate or replicate data.
- Inspect the sample container and chain of custody.
- Inspect packaging integrity and storage humidity.
- Compare supplier, receiving and finished-package results.
- Determine whether a new representative sample is justified.
- Evaluate microbiological and other related risks.
- Document the disposition and corrective action.
Retesting should not become “test until pass.” A retest plan should state why the first result may not be reliable, how the new sample will be selected and how conflicting results will be resolved.
Water activity, shelf life and storage claims
A single aw result is not a shelf-life study.
Shelf-life support may require evaluation of:
- water activity over time;
- moisture content;
- package integrity;
- microbial results;
- chemical or alkaloid stability;
- odor, color and flow changes;
- temperature and humidity exposure;
- accelerated versus real-time conditions; and
- complaint or return history.
FDA’s dietary-supplement CGMP guide states that shelf-life dating is not required by Part 111, but a manufacturer that uses an expiration or “best by” date should have data supporting it. Kiody should present this only as a quality-system benchmark and not as FDA acceptance of kratom as a dietary supplement. FDA Small Entity CGMP Guide
A proposed Kiody water-activity quality record
For each reviewed botanical powder or capsule lot, Kiody could retain:
- Product name and form.
- Supplier lot and Kiody lot.
- Quantity represented.
- Sampling plan reference.
- Sample collection date and person.
- Sample container and seal condition.
- Laboratory and testing location.
- Method reference.
- Test temperature.
- Water-activity result.
- Moisture or loss-on-drying result, if separately tested.
- Applicable internal specification and version.
- Replicate or retest information.
- Related microbial results.
- Packaging material and configuration.
- Storage condition before release.
- Reviewer and review date.
- Release, hold, rejection or other disposition.
- Deviation or corrective-action reference.
- COA and supporting-document location.
This is a proposed internal record, not a claim that one checklist satisfies every federal, state or local requirement.
Product-form distinctions
Ordinary botanical leaf powder
Water-activity and moisture results can support receiving, drying, storage and package-barrier review. They do not establish alkaloid content, botanical identity or legal status.
Pure-leaf capsules
Review both the incoming powder and finished capsule/package configuration. Capsule count and approximately 500 mg leaf fill are separate from moisture and aw measurements.
Extracts
Extract matrices can behave differently because of carriers, residual solvents, hygroscopic constituents and concentration. A powder specification should not be copied to an extract without technical justification.
Enhanced products and concentrated 7-OH
Water-activity testing does not distinguish ordinary leaf from a concentrated or enhanced alkaloid product. Composition and alkaloid testing are required for that question. Kiody does not sell concentrated 7-OH.
Mitragynine pseudoindoxyl, MGM-15 and MGM-16
These substances are subject to a separate federal temporary Schedule I order effective August 26, 2026 through August 26, 2028. A moisture or aw result has no bearing on that controlled-substance status. DEA temporary scheduling order
Frequently asked questions
Is water activity the same as moisture percentage?
No. Moisture content estimates how much water or method-defined mass loss is present. Water activity measures the equilibrium availability or energy status of water.
Can I convert 8% moisture into a water-activity value?
Not reliably from that information alone. A product-specific sorption relationship, temperature and method context would be needed.
Does low water activity kill Salmonella?
No. Low aw can prevent growth under defined conditions, but Salmonella may survive drying and persist in low-moisture material.
Does a water-activity test replace a microbial panel?
No. The tests answer different questions. Water activity does not detect or enumerate microorganisms.
Is 0.85 the legal kratom limit?
No universal federal kratom aw limit of 0.85 has been established by the cited sources. The number is used in specific food-regulatory definitions and laboratory contexts. Kiody should not present it as nationwide kratom law.
Why should the report include temperature?
Water activity changes with temperature, and the definition requires comparison under the same temperature conditions.
Can an unopened package gain moisture?
Yes. Moisture may move through packaging over time depending on barrier properties, seal integrity, humidity, temperature and storage duration.
Does a desiccant guarantee stability?
No. Its type, capacity, placement, package barrier and storage conditions all matter. It also does not remove contaminants already present.
Is loss on drying identical to water content?
Not always. Heat-based mass loss may include volatile materials in addition to water, and tightly held water may not be fully removed under every method.
Should powder and finished capsules use the same specification?
Not automatically. The finished capsule shell, bottle, headspace and closure can change the system. A qualified reviewer should justify each product specification.
What does a “Pass” water-activity result prove?
Only that the tested portion met the criterion identified on the report under the stated method and conditions. It does not prove absence of pathogens, shelf life or FDA approval.
Can water-activity testing tell whether a product contains concentrated 7-OH?
No. That requires appropriate composition and alkaloid testing. Kiody does not sell concentrated 7-OH.
Primary sources
- U.S. Food and Drug Administration, Water Activity (aw) in Foods.
- Electronic Code of Federal Regulations, 21 CFR Part 117.
- U.S. Department of Agriculture, Agricultural Research Service, Water Activity in Food.
- U.S. Food and Drug Administration, BAM Chapter 5: Salmonella.
- U.S. Food and Drug Administration, Sampling for Foodborne Biological Hazards.
- U.S. Food and Drug Administration, BAM: Yeasts, Molds and Mycotoxins.
- U.S. Food and Drug Administration, Draft Guidance on Sanitation Programs for Low-Moisture Ready-to-Eat Human Foods.
- U.S. Food and Drug Administration, FDA and Kratom.
- Drug Enforcement Administration, Temporary Schedule I Order for Mitragynine Pseudoindoxyl, MGM-15 and MGM-16.