Does Oxalic Acid Affect Honey Quality? A Full-Season Study

Does Oxalic Acid Affect Honey Quality? A Full-Season Study

Does oxalic acid affect honey quality? A study published in April 2026 by a team at the University of Belgrade says no. Across a 17-week season they tested 183 honey samples and 187 beeswax samples from treated and untreated colonies and found no measurable difference in composition between them. Thymol came out the same way. That is a useful answer to a question beekeepers ask every August, and it is also a narrower answer than the headline makes it sound, so it is worth walking through exactly what got measured.

The question usually surfaces right before a harvest. Mites are climbing, the supers are on or about to come off, and somebody at the club meeting says the acid will end up in the jar. It is a fair worry. Synthetic acaricides really do accumulate — amitraz breakdown products, coumaphos and fluvalinate build up in comb year over year, and that record is one of the main reasons beekeepers moved to organic acids in the first place.

What has been thin is season-long data on whether the organic treatments do the same thing to a crop. This study went after it in an unusual way.

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What the study did: ten colonies, 17 weeks, 370 samples

The work was run by Stankovic, Nikcevic, Spasic and Radotic at the Institute for Multidisciplinary Research, University of Belgrade, and published in the journal Insects in April 2026. The field season was 2020, at an apiary in Odusevac, Stari Slankamen, in northern Serbia.

Ten nucleus colonies were split into three groups: four untreated controls, three treated with oxalic acid, three treated with thymol. Treatment ran from 15 June to 11 October. The oxalic acid group received 36 grams per hive, delivered as a 1:1:1 mix of oxalic acid, glycerin and water soaked into shop towels laid across the top bars — the homemade version of an extended-release strip. The thymol group got Apiguard trays at 25% thymol, replaced every 28 days.

Every week the team pulled honey from uncapped cells at the same location on the same frame, plus wax from those frames. That came to 183 honey samples and 187 beeswax samples, all multifloral honey. Each sample went under a spectrofluorometer, and the number they extracted was the ratio of protein fluorescence to phenolic fluorescence — a fast composite reading of two things a colony puts into its honey and wax. Two weeks of pre-treatment sampling in early June confirmed the three groups started level.

Does oxalic acid leave residue in honey? What the numbers showed

Nothing moved. Here is the whole result in two rows.

Read the two middle columns together. Treatment did nothing the instrument could see. Time of year did plenty. Honey and wax composition drifted across the season the way anyone would expect as the forage changed, and the treated colonies drifted along with the controls instead of away from them. The authors also reported no decline in bee population in either treatment group relative to the controls over those 17 weeks.

Does oxalic acid change beeswax?

Same answer, and this half of the result is arguably the more useful one. Wax is where acaricide problems show up. It is fat-soluble, it sits in the box for years, and the residue literature on synthetic miticides is largely a record of comb slowly loading up until the contamination starts showing in queens and brood.

Oxalic acid is water-soluble and does not partition into wax the way those compounds do, which is the mechanistic reason to expect this outcome rather than a surprise. The Belgrade data is consistent with it: 187 wax samples across a full season, no treatment signal. If you rotate out old comb because of what previous treatments left behind in it, nothing here suggests oxalic acid is adding to that pile. That is part of why we point people at EPA-registered oxalic acid rather than a synthetic strip when they ask what to keep in the truck.

What the study does not show

Three things, and they matter more than the headline.

First, this is not a residue assay. Nobody measured milligrams of oxalic acid per kilogram of honey. The protein-to-phenolic ratio tracks the honey's own constituents, so the finding is "treatment did not disturb what the bees put in the jar", not "no acid reached the jar". For actual residue figures you still go back to Bogdanov's fieldwork, which measured 8–51 mg/kg of oxalic acid in untreated blossom honey and 38–119 mg/kg in honeydew honey — it is already in there, naturally — and found no meaningful rise after autumn treatment.

Second, the sample is small. Three hives per treatment group, one apiary, one season. The authors say as much themselves and note that the absence of an effect may partly reflect limited statistical power. A null result from three hives is weaker evidence than a null result from thirty, and it should be read that way.

Third, and most relevant to anyone reading this: the oxalic acid here was not vaporized. Glycerin towels bleed acid into a colony over weeks. A vaporizer deposits crystal on surfaces in about a minute and is done. Different route, different exposure curve, and the study cannot speak to one from the other. The one thing that does carry across is total load: 36 grams of oxalic acid per hive over a season is far more acid than vaporizing puts in, where 2 grams per deep box per treatment is the working dose and even a heavy year of treatments lands well under that figure. If the larger load left the honey alone, the smaller one is unlikely to be the problem. That is a reasonable inference. It is not a finding.

Worth adding that the data is five years old — collected in 2020, published in 2026. Nothing improper about that, it is simply not fresh news from this season.

Is honey safe after oxalic acid treatment?

For honey you harvest after a fall treatment, the picture is about as settled as beekeeping evidence gets. Oxalic acid occurs naturally in honey at levels above anything a treatment adds, the taste threshold sits several times higher again, and both the EZ-OX and Api-Bioxal labels permit application with supers on the hive.

We still would not treat during an active flow. Not because we think it ruins a crop, but because no one has published a residue study for vaporizing with supers on and filling, and "the label allows it" is a weaker statement than "somebody measured it". We laid that position out in full in our guide to treating bees during the honey flow, and this study does not change it. Pull the supers, then treat.

What it means for how you actually treat

Not much, which is rather the point of a null result. If you have been holding off on oxalic acid because you were worried about the crop, here is one more reason to stop worrying. If you were already treating, carry on.

The things that decide whether a treatment works are unchanged. Two grams per deep box is still the working dose; the EPA amended the EZ-OX label in January 2026 to allow 2 to 4 grams per deep body, and that top end is headroom for a colony in genuine trouble rather than a new target. Our page on how much oxalic acid to use per hive covers the schedule. Capped brood shields mites from vapor, so a single mid-season treatment cannot reach most of the mite population — the broodless windows, the last warm day of fall and the first warm day of late winter, are where the same 2 grams does its best work.

And whichever product you use, wash before and after. A composition study tells you the treatment did not hurt your honey. It tells you nothing about whether it killed your mites, and only a mite wash answers that.

• Stop worrying about the jar. Two independent lines of evidence — Bogdanov's residue work and now a full season of composition sampling — point the same direction. Oxalic acid is not contaminating your honey.
• Still pull supers during a flow. The label permits supers on. The direct residue evidence for vaporizing with supers on and filling does not exist yet. Treat after the harvest.
• Wax is the quiet win. Oxalic acid does not build up in comb the way the synthetics do. If comb contamination is why you rotate frames out, an organic acid program is not adding to it.
• Do not read a null result as proof. Three hives per group is a small study, and the authors say so. It supports a conclusion; it does not settle one.
• Dose and timing still decide the outcome. 2 grams per deep box, in a broodless window, beats a bigger number at the wrong time of year.
• Count before and after. A treatment you did not measure is a treatment you are guessing about.

Related reading

• Does oxalic acid vaporization actually work? What the studies show
• Which oxalic acid should you use: EZ-OX vs Api-Bioxal vs wood bleach
• How much oxalic acid per hive, and on what schedule
• How to use an oxalic acid vaporizer safely

Sources

• Stankovic, M., Nikcevic, M., Spasic, S.Z. & Radotic, K., “Assessing the Effects of Thymol and Oxalic Acid on Honey Bee Colony Condition Using Ratiometric Spectral Indicators in Honey and Beeswax”, Insects 17(4):440, 2026
• Bogdanov, S. et al., “Determination of residues in honey after treatments with formic and oxalic acid under field conditions”, Apidologie 33:399–409, 2002
• Sagona, S. et al., “Effect of Oxalic Acid on Honey Bee Physiology”, Insects 15(6):409, 2024
• Rademacher, E. & Harz, M., “Oxalic acid for the control of varroosis in honey bee colonies — a review”, Apidologie 37(1):98–120, 2006
• EZ-OX Tablets label, EPA Reg. No. 101743-2, accepted 27 January 2026, US EPA

Happy Beekeeping from the Lorob Bees Team

General beekeeping information, not a substitute for the product label. Always read and follow the label of any product you use in a hive.