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Honey

Honey

Honey is a sweet, viscous food substance made by bees and some other bees.[1][2] Bees produce honey from the sugary secretions of plants (floral nectar) or from secretions of other insects (such as honeydew), by regurgitation, enzymatic activity, and water evaporation. Honey bees store honey in wax structures , whereas stingless bees store honey in pots made of wax and resin.[1][2][3] honeyThe variety of produced by honey bees (the genus Apis) is the best-known, due to its worldwide commercial production and human consumption.[4] Honey is collected from wild bee colonies, or from hives of domesticated bees, a practice known as beekeeping or apiculture (meliponiculture in the case of stingless bees).

Honey gets its sweetness from the monosaccharides fructose and glucose, and has about the same relative sweetness as sucrose (table sugar).[5][6] Fifteen millilitres (1 US tablespoon) of honey provides around 190 kilojoules (46 kilocalories) of food energy.[7] It has attractive chemical properties for baking and a distinctive flavor when used as a sweetener.[5] Most microorganisms do not grow in honey, so sealed honey does not spoil, even after thousands of years.[8][9]

French honey from different floral sources, with visible differences in color and texture

Honey use and production have a long and varied history as an ancient activity. Several cave paintings in Cuevas de la Araña in Spain depict humans foraging for honey at least 8,000 years ago.[10][11] Large-scale meliponiculture has been practiced by the Mayans since pre-Columbian times.[2][12]

Formation

A honey bee on calyx of goldenrod with its proboscis extended

Honey is produced by bees collecting nectar and honeydew for use as sugars consumed to support metabolism of muscle activity during foraging or to be stored as a long-term food supply.[13][14] During foraging, bees access part of the nectar collected to support metabolic activity of flight muscles, with the majority of collected nectar destined for regurgitation, digestion, and storage as honey.[13][15] In cold weather or when other food sources are scarce, adult and larval bees use stored honey as food.[14]

By contriving for honey bee swarms to nest in human-made hives, people have been able to semidomesticate the insects and harvest excess honey. In the hive or in a wild nest, the three types of bees are:

  • a single female queen bee
  • a seasonally variable number of male drone bees to fertilize new queens
  • 20,000 to 40,000 female worker bees[16]

Leaving the hive, a foraging bee collects sugar-rich flower nectar, sucking it through its proboscis and placing it in its proventriculus (honey stomach or crop), which lies just dorsal to its food stomach. In Apis mellifera, the honey stomach holds about 40 mg of nectar, or roughly 50% of the bee’s unloaded weight, which can require over a thousand flowers and more than an hour to fill. The nectar generally begins with a water content of 70 to 80%.[17] Salivary enzymes and proteins from the bee’s hypopharyngeal gland are added to the nectar to begin breaking down the sugars, raising the water content slightly. The forager bees then return to the hive, where they regurgitate and transfer nectar to the hive bees. The hive bees then use their honey stomachs to ingest and regurgitate the nectar, forming bubbles between their mandibles repeatedly until it is partially digested. The bubbles create a large surface area per volume and a portion of the water is removed through evaporation.[13][15][18][19] The bee’s digestive enzymes hydrolyze converts sucrose to a mixture of glucose and fructose, and break down other starches and proteins, increasing the acidity.[13][15][20]

The bees work together as a group with the regurgitation and digestion for as long as 20 minutes, passing the nectar from one bee to the next, until the product reaches the honeycombs in storage quality.[15] It is then placed in honeycomb cells and left unsealed while still high in water content (about 50 to 70%) and natural yeasts which, unchecked, would cause the sugars in the newly formed honey to ferment.[14][21][22] Bees are among the few insects that can generate large amounts of body heat, and the hive bees constantly regulate the hive temperature, either heating with their bodies or cooling with water evaporation, to maintain a fairly constant temperature of about 35 °C (95 °F) in the -storage areas. The process continues as hive bees flutter their wings constantly to circulate air and evaporate water from the honey to a content around 18%, raising the sugar concentration beyond the saturation point and preventing fermentation.[14][15] The bees then cap the cells with wax to seal them.[15] As removed from the hive by a beekeeper,  has a long shelf life and will not ferment if properly sealed.[14]

Some wasp species, such as Brachygastra lecheguana and Brachygastra mellifica found in South and Central America, are known to feed on nectar and produce honey.[23]

Some wasps, such as Polistes versicolor, consume honey, alternating between feeding on pollen in the middle of their lifecycles and feeding on honey, which can better provide for their energy needs.[24]

Production

Collection

Sealed frame

Extraction from a comb

Filtering from a comb

Honey is collected from wild bee colonies or from domesticated beehives. On average, a hive will produce about 29 kilograms (65 lb) of per year.[25] Wild bee nests are sometimes located by following a honeyguide bird.

To safely collect honey from a hive, beekeepers typically pacify the bees using a bee smoker. The smoke triggers a feeding instinct (an attempt to save the resources of the hive from a possible fire), making them less aggressive, and obscures the pheromones the bees use to communicate. The honeycomb is removed from the hive and the may be extracted from it either by crushing or by using a honey extractor. The honey is then usually filtered to remove beeswax and other debris.

Before the invention of removable frames, bee colonies were often sacrificed to conduct the harvest. The harvester would take all the available honey and replace the entire colony the next spring. Since the invention of removable frames, the principles of husbandry led most beekeepers to ensure that their bees have enough stores to survive the winter,[citation needed] either by leaving some honey in the beehive or by providing the colony with a honey substitute such as sugar water or crystalline sugar (often in the form of a “candyboard”). The amount of food necessary to survive the winter depends on the variety of bees and on the length and severity of local winters.

Many animal species are attracted to wild or domestic sources o[26]

Preservation

Because of its composition and chemical properties, honey is suitable for long-term storage, and is easily assimilated even after long preservation. Honey, and objects immersed in honey, have been preserved for centuries.[27][28] The key to preservation is limiting access to humidity. In its cured state, honey has a sufficiently high sugar content to inhibit fermentation. If exposed to moist air, its hydrophilic properties pull moisture into the honey, eventually diluting it to the point that fermentation can begin.[29]

The long shelf life of honey is attributed to an enzyme found in the stomach of bees. The bees mix glucose oxidase with expelled nectar they previously consumed, creating two byproducts – gluconic acid and hydrogen peroxide, which are partially responsible for honey acidity and suppression of bacterial growth.[8]

Adulteration

Honey is sometimes adulterated by the addition of other sugars, syrups, or compounds to change its flavor or viscosity, reduce cost, or increase the fructose content to stave off crystallization. Adulteration of honey has been practiced since ancient times, when honey was sometimes blended with plant syrups such as maple, birch, or sorghum and sold to customers as pure honey. Sometimes crystallized honey was mixed with flour or other fillers, hiding the adulteration from buyers until the honey was liquefied. In modern times the most common adulterant became clear, almost-flavorless corn syrup; the adulterated mixture can be very difficult to distinguish from pure honey.[30]

According to the Codex Alimentarius of the United Nations, any product labeled as “honey” or “pure honey” must be a wholly natural product, although labeling laws differ between countries.[31] In the United States, according to the National Honey Board (NHB;[32] supervised by the United States Department of Agriculture),[33][34] “honey stipulates a pure product that does not allow for the addition of any other substance… this includes, but is not limited to, water or other sweeteners”.[35]

Isotope ratio mass spectrometry can be used to detect addition of corn syrup and cane sugar by the carbon isotopic signature. Addition of sugars originating from corn or sugar cane (C4 plants, unlike the plants used by bees, and also sugar beet, which are predominantly C3 plants) skews the isotopic ratio of sugars present in honey,[36] but does not influence the isotopic ratio of proteins. In an unadulterated honey, the carbon isotopic ratios of sugars and proteins should match. Levels as low as 7% of addition can be detected.[37]

Worldwide production

Production of natural honey in 2019
Country Production
(tonnes)
 China 444,100
 Turkey 109,330
 Canada 80,345
 Argentina 78,927
 Iran 75,463
 United States 71,179
World 1,852,598
Source: FAOSTAT[38]

In 2019, global production of honey was 1.9 million tonnes, led by China with 24% of the world total (table).[38] Other major producers were Turkey, Canada, Argentina, and Iran.[38]

Modern uses

Food

Over its history as a food,[10] the main uses of honey are in cooking, baking, desserts, as a spread on bread, as an addition to various beverages such as tea, and as a sweetener in some commercial beverages.[citation needed]

Due to its energy density, honey is an important food for virtually all hunter-gatherer cultures in warm climates, with the Hadza people ranking honey as their favorite food.[39] Honey hunters in Africa have a mutualistic relationship with certain species of Honeyguide birds.[40]

Fermentation

Possibly the world’s oldest fermented beverage, dating from 9,000 years ago,[41] mead (“honey wine”) is the alcoholic product made by adding yeast to honey-water must and fermenting it for weeks or months.[42][43] The yeast Saccharomyces cerevisiae is commonly used in modern mead production.[42][43]

Mead varieties include drinks called metheglin (with spices or herbs), melomel (with fruit juices, such as grape, specifically called pyment), hippocras (with cinnamon), and sack mead (high concentration of honey),[43] many of which have been developed as commercial products numbering in the hundreds in the United States.[44] Honey is also used to make mead beer, called “braggot”.[45]

Physical and chemical properties

Crystallized honey: The inset shows a close-up of the honey, showing the individual glucose grains in the fructose mixture.

The physical properties of honey vary, depending on water content, the type of flora used to produce it (pasturage), temperature, and the proportion of the specific sugars it contains. Fresh honey is a supersaturated liquid, containing more sugar than the water can typically dissolve at ambient temperatures. At room temperature, honey is a supercooled liquid, in which the glucose precipitates into solid granules. This forms a semisolid solution of precipitated glucose crystals in a solution of fructose and other ingredients.[citation needed]

The density of honey typically ranges between 1.38 and 1.45 kg/l at 20 °C.[46]

Phase transitions

The melting point of crystallized honey is between 40 and 50 °C (104 and 122 °F), depending on its composition. Below this temperature, honey can be either in a metastable state, meaning that it will not crystallize until a seed crystal is added, or, more often, it is in a “labile” state, being saturated with enough sugars to crystallize spontaneously.[47] The rate of crystallization is affected by many factors, but the primary factor is the ratio of the main sugars: fructose to glucose. Honeys that are supersaturated with a very high percentage of glucose, such as brassica honey, crystallize almost immediately after harvesting, while honeys with a low percentage of glucose, such as chestnut or tupelo honey, do not crystallize. Some types of honey may produce few but very large crystals, while others produce many small crystals.[48]

Crystallization is also affected by water content, because a high percentage of water inhibits crystallization, as does a high dextrin content. Temperature also affects the rate of crystallization, with the fastest growth occurring between 13 and 17 °C (55 and 63 °F). Crystal nuclei (seeds) tend to form more readily if the honey is disturbed, by stirring, shaking, or agitating, rather than if left at rest. However, the nucleation of microscopic seed-crystals is greatest between 5 and 8 °C (41 and 46 °F). Therefore, larger but fewer crystals tend to form at higher temperatures, while smaller but more-numerous crystals usually form at lower temperatures. Below 5 °C, the honey will not crystallize, thus the original texture and flavor can be preserved indefinitely.[48]

Honey is a supercooled liquid when stored below its melting point, as is normal. At very low temperatures, honey does not freeze solid; rather its viscosity increases. Like most viscous liquids, the honey becomes thick and sluggish with decreasing temperature. At −20 °C (−4 °F), honey may appear or even feel solid, but it continues to flow at very low rates. Honey has a glass transition between −42 and −51 °C (−44 and −60 °F). Below this temperature, honey enters a glassy state and becomes an amorphous solid (noncrystalline).[49][50]

Rheology

Pouring raw honey. The sheet-like appearance of the flow is the result of high viscosity and low surface tension, contributing to the stickiness of honey.[51][52]

The viscosity of honey is affected greatly by both temperature and water content. The higher the water percentage, the more easily honey flows. Above its melting point, however, water has little effect on viscosity. Aside from water content, the composition of most types of honey also has little effect on viscosity. At 25 °C (77 °F), honey with 14% water content generally has a viscosity around 400 poise, while a honey containing 20% water has a viscosity around 20 poise. Viscosity increases very slowly with moderate cooling; a honey containing 16% water, at 70 °C (158 °F), has a viscosity around 2 poise, while at 30 °C (86 °F), the viscosity is around 70 poise. With further cooling, the increase in viscosity is more rapid, reaching 600 poise at around 14 °C (57 °F).[53][54] However, while honey is viscous, it has low surface tension of 50–60 mJ/m2, making its wettability similar to water, glycerin, or most other liquids.[55] The high viscosity and wettability of honey cause stickiness, which is a time-dependent process in supercooled liquids between the glass-transition temperature (Tg) and the crystalline-melting temperature.[56]

Most types of honey are Newtonian liquids, but a few types have non-Newtonian viscous properties. Honeys from heather or manuka display thixotropic properties. These types of honey enter a gel-like state when motionless, but liquefy when stirred.[57]

Electrical and optical properties

Because honey contains electrolytes, in the form of acids and minerals, it exhibits varying degrees of electrical conductivity. Measurements of the electrical conductivity are used to determine the quality of honey in terms of ash content.[54]

The effect honey has on light is useful for determining the type and quality. Variations in its water content alter its refractive index. Water content can easily be measured with a refractometer. Typically, the refractive index for honey ranges from 1.504 at 13% water content to 1.474 at 25%. Honey also has an effect on polarized light, in that it rotates the polarization plane. The fructose gives a negative rotation, while the glucose gives a positive one. The overall rotation can be used to measure the ratio of the mixture.[54][29] Honey may vary in color between pale yellow and dark brown, but other bright colors may occasionally be found, depending on the source of the sugar harvested by the bees.[58] Bee colonies that forage on Kudzu (Pueraria montana var. lobata) flowers, for example, produce honey that varies in color from red to purple.[59]

Hygroscopy and fermentation

Honey has the ability to absorb moisture directly from the air, a phenomenon called hygroscopy. The amount of water the honey absorbs is dependent on the relative humidity of the air. Because honey contains yeast, this hygroscopic nature requires that honey be stored in sealed containers to prevent fermentation, which usually begins if the honey’s water content rises much above 25%. Honey tends to absorb more water in this manner than the individual sugars allow on their own, which may be due to other ingredients it contains.[29]

Fermentation of honey usually occurs after crystallization, because without the glucose, the liquid portion of the honey primarily consists of a concentrated mixture of fructose, acids, and water, providing the yeast with enough of an increase in the water percentage for growth. Honey that is to be stored at room temperature for long periods of time is often pasteurized, to kill any yeast, by heating it above 70 °C (158 °F).[29]

Thermal characteristics

Creamed honey: the honey on the left is fresh, and the honey on the right has been aged at room temperature for two years. The Maillard reaction produces considerable differences in the color and flavor of the aged honey, which remains edible.

Like all sugar compounds, honey caramelizes if heated sufficiently, becoming darker in color, and eventually burns. However, honey contains fructose, which caramelizes at lower temperatures than glucose.[60] The temperature at which caramelization begins varies, depending on the composition, but is typically between 70 and 110 °C (158 and 230 °F). Honey also contains acids, which act as catalysts for caramelization. The specific types of acids and their amounts play a primary role in determining the exact temperature.[61] Of these acids, the amino acids, which occur in very small amounts, play an important role in the darkening of honey. The amino acids form darkened compounds called melanoidins, during a Maillard reaction. The Maillard reaction occurs slowly at room temperature, taking from a few to several months to show visible darkening, but speeds up dramatically with increasing temperatures. However, the reaction can also be slowed by storing the honey at colder temperatures.[62]

Unlike many other liquids, honey has very poor thermal conductivity of 0.5 W/(m⋅K) at 13% water content (compared to 401 W/(m⋅K) of copper), taking a long time to reach thermal equilibrium.[63] Due to its high kinematic viscosity honey does not transfer heat through momentum diffusion (convection) but rather through thermal diffusion (more like a solid), so melting crystallized honey can easily result in localized caramelization if the heat source is too hot or not evenly distributed. However, honey takes substantially longer to liquefy when just above the melting point than at elevated temperatures.[54] Melting 20 kg of crystallized honey at 40 °C (104 °F) can take up to 24 hours, while 50 kg may take twice as long. These times can be cut nearly in half by heating at 50 °C (122 °F); however, many of the minor substances in honey can be affected greatly by heating, changing the flavor, aroma, or other properties, so heating is usually done at the lowest temperature and for the shortest time possible.[64]

Acid content and flavor effects

The average pH of honey is 3.9, but can range from 3.4 to 6.1.[65] Honey contains many kinds of acids, both organic and amino. However, the different types and their amounts vary considerably, depending on the type of honey. These acids may be aromatic or aliphatic (nonaromatic). The aliphatic acids contribute greatly to the flavor of honey by interacting with the flavors of other ingredients.[65]

Organic acids comprise most of the acids in honey, accounting for 0.17–1.17% of the mixture, with gluconic acid formed by the actions of glucose oxidase as the most prevalent.[65] Minor amounts of other organic acids are present, consisting of formic, acetic, butyric, citric, lactic, malic, pyroglutamic, propionic, valeric, capronic, palmitic, and succinic, among many others.[65][66]

Volatile organic compounds

Individual honeys from different plant sources contain over 100 volatile organic compounds (VOCs), which play a primary role in determining honey flavors and aromas.[67][68][69] VOCs are carbon-based compounds that readily vaporize into the air, providing aroma, including the scents of flowers, essential oils, or ripening fruit.[67][69] The typical chemical families of VOCs found in honey include hydrocarbons, aldehydes, alcohols, ketones, esters, acids, benzenes, furans, pyrans, norisoprenoids, and terpenes, among many others and their derivatives.[67][69] The specific VOCs and their amounts vary considerably between different types of honey obtained by bees foraging on different plant sources.[67][68][69] By example, when comparing the mixture of VOCs in different honeys in one review, longan honey had a higher amount of volatiles (48 VOCs), while sunflower honey had the lowest number of volatiles (8 VOCs).[67]

VOCs are primarily introduced into the honey from the nectar, where they are excreted by the flowers imparting individual scents.[67] The specific types and concentrations of certain VOCs can be used to determine the type of flora used to produce monofloral honeys.[67][69] The specific geography, soil composition and acidity used to grow the flora also have an effect on honey aroma properties,[68] such as a “fruity” or “grassy” aroma from longan honey, or a “waxy” aroma from sunflower honey.[67] Dominant VOCs in one study were linalool oxide, trans-linalool oxide, 2-phenylacetaldehyde, benzyl ethanol, isophorone, and methyl nonanoate.[67]

VOCs can also be introduced from the bodies of the bees, be produced by the enzymatic actions of digestion, or from chemical reactions that occur between different substances within the honey during storage, and therefore may change, increase, or decrease over long periods of time.[67][68] VOCs may be produced, altered, or greatly affected by temperature and processing.[68] Some VOCs are heat labile, and are destroyed at elevated temperatures, while others can be created during non-enzymatic reactions, such as the Maillard reaction.[69] VOCs are responsible for nearly all of the aroma produced by a honey, which may be described as “sweet”, “flowery”, “citrus”, “almond” or “rancid”, among other terms.[67] In addition, VOCs play a large role in determining the specific flavor of the honey, both through the aromas and flavor.[67] VOCs from honeys in different geographic regions can be used as floral markers of those regions, and as markers of the bees that foraged the nectars.[67][68]

Classification

Honey is classified by its floral source, and divisions are made according to the packaging and processing used. Regional honeys are also identified. In the US, honey is also graded on its color and optical density by USDA standards, graded on the Pfund scale, which ranges from 0 for “water white” honey to more than 114 for “dark amber” honey.[70]

Floral source

Generally, honey is classified by the floral source of the nectar from which it was made. Honeys can be from specific types of flower nectars or can be blended after collection. The pollen in honey is traceable to floral source and therefore region of origin. The rheological and melissopalynological properties of honey can be used to identify the major plant nectar source used in its production.[71]

Blended

Most commercially available honey is a blend[72] of two or more honeys differing in floral source, color, flavor, density, or geographic origin.[73]

Polyfloral

Polyfloral honey, also known as wildflower honey,[74] is derived from the nectar of many types of flowers.[73][75] The taste may vary from year to year, and the aroma and the flavor can be more or less intense, depending on which flowers are blooming.[73]

Monofloral

Monofloral honey is made primarily from the nectar of one type of flower. Monofloral honeys have distinctive flavors and colors because of differences between their principal nectar sources.[76] To produce monofloral honey, beekeepers keep beehives in an area where the bees have access, as far as possible, to only one type of flower. In practice a small proportion of any monofloral honey will be from other flower types. Typical examples of North American monofloral honeys are clover, orange blossom, sage, tupelo, buckwheat, fireweed, mesquite, sourwood,[77] cherry, and blueberry. Some typical European examples include thyme, thistle, heather, acacia, dandelion, sunflower, lavender, honeysuckle, and varieties from lime and chestnut trees.[citation needed] In North Africa (e.g. Egypt), examples include clover, cotton, and citrus (mainly orange blossoms).[citation needed] The unique flora of Australia