HMF & Diastase: The Two Numbers That Reveal If Your Honey Was Heated

The Quality Test on Your Honey Label That Does Not Exist

When you buy a jar labelled "pure raw honey," you are trusting that the honey was never overheated, is not old enough to have degraded significantly, and has not been bulked with cheaper syrups. But the label tells you none of this. In most countries, honey can be legally sold as "pure" with no disclosure of heat treatment, enzyme status, or freshness markers.

Food scientists and regulatory agencies have two laboratory tests that do tell this story: HMF (hydroxymethylfurfural) content and diastase number (DN). Both are required by the Codex Alimentarius international honey standard and by the EU Honey Directive. Both are absent from US federal grading standards. And both, together, form a dual-marker diagnostic that reveals far more about a jar of honey than any marketing claim.

This guide explains what each marker measures, what the global standards actually require, and how to interpret HMF and diastase data when it is available.

What Is HMF? Honey's Heat and Age Fingerprint

HMF — 5-hydroxymethylfurfural — is a furan derivative that forms naturally in honey via two pathways: acid-catalysed dehydration of fructose (the Lobry de Bruyn–Alberda van Ekenstein transformation under acidic conditions) and the Maillard reaction between reducing sugars and amino acids. Both pathways accelerate dramatically with temperature.

Fresh honey extracted from the hive contains very little HMF — typically 1–5 mg/kg in freshly extracted raw honey, and often below 2 mg/kg in honey processed and bottled within weeks of harvest. HMF then increases with storage time and temperature. At ambient room temperature (~20°C/68°F), HMF can rise 5–15 mg/kg per year in a well-sealed jar. The relationship is non-linear: at 40°C (104°F) HMF formation rate roughly doubles; at 50°C (122°F) it doubles again; at 70°C (158°F) the rate is orders of magnitude faster than at room temperature (Arrhenius kinetics). This is why brief pasteurisation at 63°C and aggressive processing at 75°C+ create very different HMF signatures.

The practical implication is that HMF is a cumulative clock. Every degree and every day adds to the total. A jar with HMF of 2 mg/kg is almost certainly fresh raw honey processed recently. A jar reading 60 mg/kg was either heated, stored for years in warm conditions, or both. A jar exceeding 100 mg/kg has almost certainly been subjected to high-temperature processing or prolonged improper storage.

• Freshly extracted raw honey: 1–5 mg/kg (often <2 mg/kg)
• Raw honey after 1 year ambient storage (~20°C): 5–20 mg/kg
• Raw honey after 2+ years or storage in warm climates: 20–40 mg/kg
• Lightly heat-treated honey (mild filtering, ~40°C): 15–35 mg/kg
• Pasteurised honey (63°C/30 min): 30–60 mg/kg
• Commercially overheated honey (>70°C): 60–200+ mg/kg

What Is Diastase? The Enzyme Bees Add — That Heat Destroys

Diastase is an enzyme complex — primarily alpha-amylase, with some beta-amylase — that worker bees secrete from their hypopharyngeal (mandibular) glands into nectar during the ripening process. Its function is to break down starch into dextrins and then into maltose. In finished honey the enzyme persists and is measurable. It serves no ongoing function in the jar, but its presence (or absence) is a direct indicator of whether the honey has been heated.

Diastase activity is measured as the "diastase number" (DN) or "Schade number," reported in Schade units (also called Gothe units depending on the assay variant). The Schade method measures how quickly honey can convert a standard starch solution — a DN of 8 means the sample can completely diastify 0.01 g of starch per gram of honey per hour under standard conditions.

Fresh raw honey from most floral sources has a DN of 10–40 depending on species. Heat destroys it progressively: meaningful losses start around 45°C (113°F), significant loss occurs at 55°C (131°F) within hours, and pasteurisation at 63°C (145°F) for 30 minutes can reduce DN by 50–80%. Brief exposure to 70°C+ nearly eliminates measurable activity. This is why diastase, like HMF, functions as a processing indicator — though it measures destruction rather than accumulation.

• Fresh raw wildflower or clover honey: DN 12–35
• Fresh raw buckwheat honey: DN 15–42
• Fresh raw heather honey: DN 12–30
• Fresh raw sidr/jujube honey: DN 10–22
• Aged raw honey (1–2 years, ambient storage): DN 8–20
• Lightly heat-filtered honey: DN 5–12
• Pasteurised honey: DN 1–6
• Overheated honey: DN <1 (often undetectable)

Global Standards: What the Numbers Must Meet

The Codex Alimentarius Standard for Honey (CXS 12-1981, revised 2023) is the baseline international reference used by most national food authorities. It sets HMF at ≤40 mg/kg for all honey, with an exception of ≤80 mg/kg for honey "declared as being of tropical origin" or "declared as overheated." Diastase must be ≥8 DN, with an exception of ≥3 DN for "honey with low natural enzyme content declared as such." The EU Honey Directive (2001/110/EC, amended by Directive 2014/63/EU) matches these limits exactly.

National standards vary, reflecting local industry pressures and climate realities. Brazil allows ≤60 mg/kg HMF — a concession to its hot climate and longer supply chains. China's GB 14963-2011 sets HMF at ≤40 mg/kg but permits a lower diastase minimum of ≥4 DN. India's FSSAI standard accepts ≥3 DN diastase for all honey types (not just declared low-enzyme varieties), and sets HMF at ≤40 mg/kg. The UK retained the EU limits post-Brexit.

The United States is the notable absence. The USDA honey grading standards (Grade A/B/C) evaluate color, clarity, moisture, and absence of fermentation. There is no federal HMF maximum and no diastase minimum in USDA Grade Standards. The FDA honey definition requires "the natural sweet substance produced by honey bees" but does not require laboratory quality markers. This means honey processed to HMF levels that would fail EU import controls can legally be sold as "pure honey" in US retail.

• Codex Alimentarius (CXS 12-1981, rev. 2023): HMF ≤40 mg/kg (80 tropical/declared); Diastase ≥8 DN (≥3 low-enzyme declared)
• EU Honey Directive 2001/110/EC (amended 2014): HMF ≤40 mg/kg (80 declared high-temp); Diastase ≥8 DN (≥3 low-enzyme declared)
• UK Honey Regulations 2015 (retained EU): HMF ≤40 mg/kg; Diastase ≥8 DN
• Brazil MAPA IN 11/2000: HMF ≤60 mg/kg; Diastase ≥8 DN
• China GB 14963-2011: HMF ≤40 mg/kg; Diastase ≥4 DN
• India FSSAI (FSSR 2011): HMF ≤40 mg/kg; Diastase ≥3 DN
• Japan: HMF ≤40 mg/kg (JAS Fair Competition Code); Diastase ≥4 DN
• USA USDA Grade Standards: No HMF limit; No diastase minimum

Which Honey Types Have Naturally Low Diastase? The Low-Enzyme Exception

Not all honey has high natural diastase activity. The enzyme level in finished honey depends on the secretory activity of the bees' hypopharyngeal glands and the enzyme content of the nectar itself — both of which vary significantly by floral source.

Acacia honey (from Robinia pseudoacacia, the black locust tree) is the most widely recognised naturally low-diastase honey. Even freshly extracted acacia honey from non-heated processing typically shows DN of 1–5 — well below the standard ≥8 threshold. This is not a quality defect: it reflects the botanical characteristics of the nectar source. The EU Honey Directive explicitly recognises this and permits ≥3 DN for honey "with a low natural enzyme content" provided this is declared on the label.

Citrus blossom honey (orange, lemon, grapefruit) is the second major category with naturally low diastase, typically DN 2–8 when fresh and unheated. Some light floral honeys — including certain lavender and clover batches — can also fall in the 4–8 DN range naturally. For these varieties, the presence of the low-enzyme exception (DN ≥3) is not suspicious; it is the correct standard to apply.

The practical consequence: a DN of 4 in an acacia honey is excellent; a DN of 4 in a wildflower honey is a warning sign. This is why the floral source matters when interpreting diastase data, and why blanket single-number comparisons across all honey types are misleading.

• Acacia (Robinia pseudoacacia): DN 1–5 naturally (exception standard ≥3 applies)
• Orange / citrus blossom: DN 2–8 naturally (exception may apply)
• Lavender: DN 3–10 (borderline — depends on origin and vintage)
• Clover: DN 8–20 (standard ≥8 threshold applies)
• Wildflower / polyfloral: DN 10–35 (standard ≥8 threshold applies)
• Buckwheat: DN 15–42 (high diastase; very heat-sensitive variety)
• Heather (Calluna vulgaris): DN 12–30 (high diastase expected)
• Sidr / Ziziphus: DN 10–22 (standard threshold applies)
• Manuka: DN 5–20+ (variable; exception may legitimately apply to some batches)

Reading HMF and Diastase Together: The Dual-Marker Diagnostic

The real analytical power comes from reading HMF and diastase together, because they respond to heat in opposite directions: HMF rises, diastase falls. This creates a diagnostic signature that is harder to fake than either marker alone.

Fresh, genuinely raw honey from a cold-climate or temperate source shows low HMF (1–5 mg/kg) and high diastase (15–40 DN). As honey ages at ambient temperature without heat, HMF rises slowly while diastase falls slowly — a compliant jar of well-stored raw honey after two years might show HMF 15–25 mg/kg and DN 10–18. This is still clearly within standards and still consistent with no heat treatment.

The signature of processed honey is different: HMF rises steeply while diastase collapses. A jar showing HMF 50 mg/kg and DN 2 has been heated, regardless of what the label claims. A jar showing HMF 80 mg/kg and DN < 1 has been aggressively heat-processed or stored at elevated temperature for extended periods. This pattern cannot occur through cold storage alone and is the primary signature of heating.

A third pattern — very low HMF and very low diastase — can indicate adulteration with high-fructose corn syrup (HFCS) or invert sugar syrup. HFCS itself has low HMF (it is industrially produced and promptly bottled) and zero diastase (it contains no bee-derived enzymes). A blended honey-HFCS product may therefore show low HMF (masking the adulteration) while having abnormally low diastase relative to the declared floral source. This is one reason food fraud investigations use HMF and diastase alongside pollen analysis and C4 sugar carbon isotope testing (δ¹³C) rather than in isolation.

• Ideal fresh raw honey: HMF 1–5 mg/kg + DN 15–40 (any standard floral type)
• Aged but authentic raw honey: HMF 10–30 mg/kg + DN 8–18 (within compliance)
• Borderline / borderline-processed: HMF 30–40 mg/kg + DN 4–8 (questionable)
• Pasteurised or heat-treated: HMF 40–80 mg/kg + DN <4 (outside most standards)
• Overheated or fraudulent: HMF >80 mg/kg + DN <1 (fails Codex and EU)
• Possible adulteration signal: HMF <5 mg/kg + DN <3 in a non-acacia/citrus variety

The US Gap: Why American Honey Has No Federal HMF Limit

The absence of HMF and diastase limits from USDA honey grading standards is not an oversight — it reflects deliberate regulatory choices about which aspects of quality the federal government mandates versus leaves to market forces. USDA Grade Standards focus on sensory quality: moisture content (≤18.6% for Grade A), absence of defects, clarity, and color. These are characteristics a buyer can evaluate without a laboratory.

The practical result is a two-tier market. Honey exported to the EU or UK must meet 40 mg/kg HMF and 8 DN diastase to clear customs — European border surveillance regularly intercepts non-compliant batches, particularly from high-volume exporters. Honey sold domestically within the US faces no equivalent chemical quality threshold. Industry associations (the American Honey Producers Association, the National Honey Board) promote quality guidelines, and some retailers impose internal standards, but neither is enforceable.

For consumers, this matters most when buying imported honey at price points that suggest commercial-scale blending. A 340g jar of "pure" clover honey priced at $3–4 is unlikely to have been cold-extracted, gently filtered, and promptly bottled from single-source US hives. Whether it meets EU standards — standards its country of origin may impose on its own producers — is not something the label will tell you.

How to Source Honey with Verified HMF and Diastase Data

Laboratory HMF and diastase data is available for honey, but finding it requires knowing where to look. The most transparent source is a Certificate of Analysis (CoA) from the producer or supplier — a document showing the batch-specific laboratory test results for moisture, HMF, diastase, sugar profile, and often pollen analysis. Artisan producers who sell direct-to-consumer increasingly provide CoA data on request or via a QR code on the label, particularly in the UK, EU, and Australia where standards are enforced at the border.

For premium honeys — particularly Mānuka, Sidr, and certified monofloral varieties — third-party laboratory certification is now common. New Zealand Mānuka Honey's MPI Science Definition requires accredited laboratory testing. Australian Mānuka Association certification includes enzyme and HMF data. A serious premium honey producer will almost always be able to provide batch-level quality data if asked.

When data is not available, a few proxy signals are worth using: look for harvest year on the label (fresh honey is lower HMF); prefer producers who are transparent about their source region and floral type (traceability correlates with quality monitoring); and favour honey that shows natural crystallisation — heavily processed or very old honey is often liquefied by heating, and a jar that has never crystallised in years of storage is worth questioning.

• Ask for a Certificate of Analysis (CoA) — legitimate producers provide these
• Look for harvest year or "best before" date with transparent provenance
• EU/UK/AU-imported honey must meet HMF ≤40 mg/kg and DN ≥8 to clear customs
• Premium monofloral and origin-certified honey (Mānuka, Sidr, PDO) often includes third-party lab data
• Crystallisation at room temperature is consistent with genuine raw honey (not proof, but consistent)
• Very cheap honey in large containers from non-transparent supply chains carries higher adulteration risk
• Honey certification audit — what USDA Organic, Non-GMO, and UMF actually test for
• How to store honey correctly — storage conditions that slow HMF formation