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Thymolised Syrup

For autumn syrup

This page has been much modified from Dave Cushman's original page. It includes information about the benefits of thymolised syrup and three methods of making it.

ROB Manley is often credited with being the first person to advocate the use of thymol in syrup for feeding bees, but this is erroneous. Manley's first book "Honey Production in the British Isles" was published in 1936, some time after an article in "The Bee World" written by "A.D.B." (Annie Betts - Editor) dated May 1931, which referred to an article in Bee Craft dated January 1931, mentioning the use of thymol to prevent fermentation of syrup. Manley wasn't mentioned in the article, but others were, suggesting that Manley may have got the idea from someone else, but due to it being in a book, therefore more permanent, Manley has probably been given credit that may have been due to others.

It seems that a Dr Killick was involved with others, including Manley, in correspondence, so I guess thymol was used for some time before 1931, making the usual "cut and pasted" words often seen on the web that "thymol has been used in syrup since the 1940s" a long way out. Manley states in his book "Honey Farming" (1946) that he thought that Dr Killick was the first to recommend it, so he clearly wasn't claiming credit himself. The history doesn't bother us now, but it is Manley who promoted it and it is "Manley's recipe" or "Manley strength" that is often quoted, so I will do so here.

Thymol is a powerful disinfectant and fungicide that is readily available online or through beekeeping suppliers. It is supplied in the form of crystals, somewhat finer than granulated sugar. It doesn't dissolve readily in water, but does in alcohol. Many references, including the earlier ones, suggest using surgical spirit, also known as "rubbing alcohol". I am not a chemist, but I have been told that isopropyl alcohol (also known as isopropanol) is a "cleaner" alcohol that is less likely to leave residues.

There is much information on the internet, with other substances, such as methylated spirits also being advocated. A search online will show different strengths and mixtures. It seems from the various suggestions that they are all suitable, but when I am dealing with something I have little knowledge of I tend to be cautious. For that reason I only use pure isopropyl alcohol. It costs a small amount more, but if kept sealed it lasts a long time.

For Manley's recipe I have copied and pasted from Dave Cushman's original page, but I have edited it slightly for clarity.

"By using surgical spirit we can first produce a "stock solution" that is miscible with sugar syrup or honey.

Manley's recipe has become a standard and even if the requirement is for a stronger solution, this is often specified as "3x Manley strength" or "4x Manley strength". This does not mean making the solution 3 or 4 times stronger, but using 3 or 4 times the amount of the stock solution in the same amount of syrup.

Manley's original recipe (known as "Manley strength") was one ounce of thymol crystals dissolved in five fluid ounces of surgical spirit to make the stock solution. Then half a fluid ounce of this mixture was added to 1 Cwt (112lbs) of sugar, which he dissolved in 7 imperial gallons (8.75 US Gal.) of water for direct use as winter feed. These obsolete units convert directly into 28.5gm thymol crystals to 142 ml surgical spirit which is a ridiculous way of expressing it. However 30gm thymol dissolved in 150 ml of surgical spirit will give a solution of the same strength and the figures are both more manageable and more easily remembered.

The stock solution is added to syrup at the rate of one teaspoon to a three gallon (imperial) quantity of syrup. This converts to 5ml of stock solution in 13.5litres, which is not a brilliant way of describing it, but the final strength is not critical. I have several plastic 'jerry' cans that hold 15 litres and I use 1, 2, 3 or 4 teaspoons of concentrate according to the strength that I require."


A simple way of making the stock solution is to dissolve 30g of thymol crystals in 150ml of isopropyl alcohol. I find this is best done in a wide necked airtight container, such as a honey jar. This makes it easy to remove a teaspoon of solution without spilling. For the ordinary amateur beekeeper this amount goes a long way and will keep for a long time. It might be helpful to know that 150ml of isopropyl alcohol weighs 118g.

"Manley strength" will prevent unsealed syrup fermenting in the combs during the winter. Fermented stores can cause bad dysentery, usually resulting in bees defecating within the hive, which will spread nosema if it is present to any great degree. Thymolised syrup will prevent syrup in containers and feeders fermenting and growing the black fungal sludge that can quickly appear, making cleaning so difficult. With care you can keep thymolised syrup in a container for some time, often from one year to the next. The cleaning of feeders and containers is much easier. There is much information available on the internet about thymolised syrup, much from amateur beekeepers, but few mention the syrup strength that Manley used, which was the old ratio of 2lb sugar to 1pint of water, or modern equivalent of 4 kg sugar to 2.5 litres of water, which very neatly makes around 5 litres of syrup.

Thymolised syrup at 3-4 times Manley strength has long been suggested as an effective treatment against nosema (Nosema apis), but of course this is often dismissed as "anecdotal evidence". There are two papers widely available that show results of experiments supporting the use of thymol against nosema. These are accessible as PDFs from the buttons on the top left. The R.N. Rice report by courtesy of the Australian Rural Industries Research & Development Corporation (RIRDC), the Yücel and Doğaroğlu study by courtesy of Pakistan Journal of Biological Sciences.

There is a further paper by Cecilia Costa et al (courtesy of HAL), accessible by the buttons that shows that thymol is also effective against Nosema ceranae.

Randy Oliver has an article on his website, the "Nosema Twins - Part 5 Alternative Treatments" that gives some useful information, including the use of thymolised, or what he calls "thymolated" syrup.

Thymolised syrup made in the above way that Manley did can mean the thymol separates out and floats to the top of the syrup if left to stand, which varies the concentration. It has been found that lecithin will emulsify the mixture, so it mixes easily and permanently, preventing separation. A websearch reveals that lecithin is a substance that occurs in animal and plant tissue. It is widely used as a food additive, so unlikely to be a problem to bees. It isn't clear who the first person to come up with the idea of using lecithin was, so I give no credits.

There is much information online about using lecithin, mostly using similar wording, quantities and procedure, suggesting a lot of "cut and paste", which may have been displayed by people who have never used it.

Below I have put together in italics a method that is based on the online information, which I have used and it works. I have followed it with my own modification on the italicised text, which I now use and suggest reading.

The above gives the same quantity and strength as Manley's original. Most sources suggest the syrup will turn "milky", but I find this doesn't happen, although the "stock solution" does.

The following is my variation on the italicised "standard" method above. I find this an easier way of doing the same thing and saves measuring because it uses items that we all have.

The quantities aren't that important, so measuring out the ingredients as described below gives virtually the same strength. It is helpful to know that a heaped teaspoonful of thymol crystals weighs around 10g, a level teaspoon is around 5ml, a level dessert spoon is around 10ml and a 1lb honey jar holds about 320ml of liquid. There are variations, e.g. I found that a heaped teaspoon of thymol using the same spoon varied between 8-12gms. Here is what I have modified the above method into.

Whichever way you make thymolised syrup remember that "Manley's strength" is one teaspoon to 13.5 litres of syrup that is made at the rate of 4kg sugar to 2.5 litres of water. This makes 5 litres of syrup, so one teaspoon of stock solution in 10 litres of syrup is less than 1.5x Manley strength. Whatever quantity of syrup you make you will need a little mental arithmetic. I use a graduated syringe instead of a spoon.

When bees are fed gently, there is food coming in, which allows them to produce wax to cap what has already been processed. This means there is a minimal amount of unsealed stores that the bees will probably use first. If bees are fed very quickly, once they have finished the food, there is no income to produce wax with, so a much larger amount of stores is left uncapped. It is this that often ferments. For that reason it is probably more important to thymolise your syrup if you feed rapidly.

Beekeepers will need to observe regulations in their own countries. In the U.K it is illegal to use thymol as a treatment for nosema because it is not registered, but it is legal to use it to prevent fermentation and mould growth in syrup at whatever strength you feel is suitable. The NBU sheet accessible from button on top left also gives advice on thymolised syrup.

Roger Patterson.

Page updated 24/09/2019