I’m processing and jarring honey this week and pondering the different tastes and aromas of each bucketful. I hope that this two-part blog might be helpful and especially for people sitting exams soon.
You’ll be forgiven for thinking that nectar is just sugary water that turns into honey. I didn’t realise either that there is so much more to it till I studied nectar more closely. I’ve always focussed on pollen as being the main source of protein and nutrition for honey bees, with nectar and honey providing the energy. While It’s true that nectar is essentially water containing dissolved substances, the bulk of which are sugars, there are an astounding number of other ingredients too. There is great variation among plants regarding the sugar content and amount of nectar produced. Diversity depends upon the plant species and environmental conditions such as soil type and weather. Likewise, there is great variability in other substances found in nectar which accounts for the fact that no two honeys, from different harvests and hives, have exactly the same flavour and properties. Knowing a bit more about the substances found in nectar helps to make sense of it as nutrition for bees, and how the honey will crystallise, granulate and set.
Sugars can be complicated. They are the energy producing carbohydrates that are needed in both the plant and animal kingdoms. An individual honey bee needs energy to kick- start muscle activity for carrying out chores inside the hive, fuelling flight muscles for foraging trips, generating heat in the brood nest and winter cluster by isometrically contracting flight muscles.
The simple sugars are called monosaccharides, and glucose and fructose are examples of these. They can be utilised by honey bees in their present forms. Sucrose on the other hand is a more complicated disaccharide that cannot be utilised in this form and must be broken down by an enzyme called sucrase which is secreted by the mandibular, labial, thoracic, hypopharyngeal and post-cerebral glands of the honey bee. Sucrase breaks down sucrose into glucose and fructose. The plant enzyme which also breaks down sucrose is called invertase and both of these work on converting this primary sugar to glucose and fructose.
So, when a bee collects fresh nectar, it will predominantly consist of varying concentrations of sucrose in water, and will include plant enzymes, such as invertase, and some minerals. There is a wide range of nectar colours across the world but here in the UK we mostly find clearer and paler colours. However, nectar can also be yellow, orange, red, blue, green, brown or black.
Typically, the composition of nectar by weight is 1: Water 30-90 %, Sucrose 5-70%, Fructose 5-30%, Glucose 5-30%, other components up to 2%. We will look at the other components shortly.
It never ceases to amaze us how bees operate, and they will avoid nectar that has been colonised by lactic acid bacteria which have made chemical changes to the nectar. If a flower has been open for a while it is easy to understand how it can become contaminated by other visiting insects and windborne debris. Interestingly, bees will collect warmer and less viscous nectar in preference to that of a higher sugar content.
Aston and Bucknall list the detailed analysis of nectar samples in their definitive and highly regarded textbook1(Good Nutrition Good Bees), and I’ve based the information on their list along with some additional information. The quantities of all the components vary with the different plant sources. By the way, I recommend this book to anyone seeking a broader understanding of honey bee nutrition. There are not many books on the subject around at the moment, and it makes an ideal reference for students of module 2 Honey Bee Products and Forage.
Sugars: sucrose, glucose, fructose, xylose, raffinose, melezitose, trehalose, melibiose, maltose, dextrin and rhammose. Maltose is a by- product of the breakdown of sucrose and can be metabolized by honey bees. Trehalose is metabolised but is not an important blood (haemolymph) sugar for bees. However, melezitose and raffinose, both found in honeydew, cannot be metabolized. Indeed, some sugars are harmful to bees if they don’t have the enzymes needed to convert them to the safe sugars that they can digest and metabolise. These harmful sugars include: mannose, galactose, arabinose, xylose, melibiose, raffinose, stachyose and lactose. Fortunately, honey bees like sucrose best, followed by glucose, maltose and fructose. Experiments show that if they do ingest harmful sugars in pollen the nectar dilutes the toxins.
Vitamins: Vitamin C is the main one but some of the vitamin B complex are present. Bioflavonoids give plants their pigmentation and bright varied colours and are present in nectar. These are also powerful antioxidants that protect cells from damage by free radicals and they work in tandem with vitamin C enhancing the latter’s role in boosting the immune system. Small amounts of thiamine, riboflavin, pyridoxine, nicotinic acid, folic acid, biotin, and meso-inositol 2 are also found in nectar.
Amino acids: These are the building blocks for protein manufacture, and are also the breakdown products of proteins. They cannot be stored in the body so must come from food. 13 amino acids have been found in nectar and these are the most important to bees; aspartic acid, glutamic acid, serine, glycine, and alanine. Some honey such as ling heather contains plant proteins which gives it the thixotropic gel-like property makes it impossible to extract heather honey unless it has been agitated first.
Minerals: There are 28 minerals in minute amounts, and there is more potassium than any other mineral in honey (100 times as much as iron). Chlorine, sulphur, sodium, calcium, phosphorous, magnesium, silicon, iron, manganese and copper follow in order of abundance. Interestingly dark honey contains an average of 1676 ppm potassium compared with light honey which has only 205 ppm.
Trace elements: 17 have been identified in honey and these include nickel, lead, tin, silver, gold and zinc.
Organic acids: These include gluconic acid, formic acid, acetic, lactic, and citric acids. The pH of honey is usually low which makes it difficult, if not impossible, for bacteria to thrive there.
Aromatic compounds: These include alcohols and aldehydes.
Enzymes: Invertase, diastase, phosphatases, oxidases, transglucosidase, and transfructosidase.
Mucus, gums, ethereal oils and dextrin are found in nectar as well as particulate constituents such as pollen, fungi, yeasts and bacteria.
Antioxidants: Vitamin C and flavonoids.
Finally, there are derivatives of phenol which, if high levels are present, can deter honey bees due to bitterness. There are also other agents such as anti-microbial, anti-fungal, antioxidant, soporific, sedative, narcotic, attractant (aromas) hormonal, and neurotoxic (aesculin) which makes for an interesting mix of substances and might come as a surprise to you. It did to me as I had no idea that nectar is so complex.
It’s useful for beekeepers to know about the different types of nectars because they affect how honey granulates. Flowers with tubes such as hellebore, bell heather, red-hot poker, and some pea family flowers have protected nectaries and are sucrose-dominated.
Open flowers with unprotected nectaries such as apple are fructose and/ or glucose dominated and mostly have more fructose than glucose with a little sucrose as well. Glucose and fructose dominated nectars are found in cabbage (Brassicaceae), carrot (Apiacea), daisy (Asteraceae) family flowers. Dandelion and oil -seed rape honeys are high in glucose and granulate quickly. On the other hand, honey with high fructose levels such as acacia (Robinia pseudoacacia) takes a very long time to granulate. I had some acacia honey from Poland that took nearly a year to start forming small crystals in the bottom of the jar. Rosebay willowherb and Himalayan balsam honeys are also light and take a long time to granulate.
Balanced nectars have approximately equal amounts of fructose, glucose and sucrose are not very common though most of the pea family (Fabaceae) nectars are balanced with the exception of acacia and red clover which are high in fructose.
In practical beekeeping terms a nectar flow tells us that the queen will lay more eggs as it stimulates brood rearing and young workers to make wax and build comb. Older workers forage for more pollen to feed the expanding brood nest. Young undertaker bees are encouraged to clear out weak and dead brood to make way for healthy ones so effectively a nectar flow stimulates hygienic behaviour. A nectar flow also encourages a colony to turn nectar into honey to store for times of dearth and winter stores. Did you know that a colony needs around 120 kg of nectar over a year and about 70 kg is consumed during the active season to meet energy needs? Here is how to recognise a nectar flow.https://www.beelistener.co.uk/beekeeping-in-scotland/how-to-recognise-a-nectar-flow/
Next week I’ll write about the conversion of nectar to honey.
1 Aston, D., Bucknall., 2021. Good Nutrition Good Bees, Northern Bee Books.
2 Crane, E., 1980. A Book of Honey, Oxford University Press.
Havenford, G., 2010. Honey Nature’s Golden Healer, Kyle Cathie Limited.
Sawyer, R., 1988. Honey Identification, Cardiff Academic Press.