2.12 Physical Properties of Honey Flashcards
Specific gravity
1.4 (density at 20° compared to water at 4°C)
Viscosity
Viscosity depends on water content, temperature and floral source.
The more treacly, the higher the viscosity.
Viscosity declines as temperature increases.
Viscosity declines as water content increases
Viscosity measurement is not considered to be a satisfactory way to measure water content of honey accurately, but it is important in the handling of honey to understand the effect of temperature and water content on viscosity.
A simple method of measuring viscosity is to:
1. Drop a ball bearing into a jar of honey and time the fall between two points.
2. Calculate the viscosity from standard tables and formula.
The units of Viscosity are Poise.
Thixotropic honey; their viscosity falls when they are stirred, but rises when they are allowed to stand.
Hygroscopicity
Hygroscopicity means being hygroscopic, absorbing or attracting moisture from the air.
Because it is a highly concentrated “sugar” solution rich in fructose, honey can absorb water readily under certain conditions.
Honey will absorb water from the air in a damp atmosphere (hygroscopicity)
Conversely, it will lose water in a dry atmosphere.
This has implications for processing and storing.
Normal honey with a water content of 18.3% or less will absorb moisture from the air at a relative humidity above 60%.
Reaction to heat
<13°C honey will not ferment
14°-18°C honey will crystallise in best manner
35°C granulated honey becomes manageable
54°C honey liquefies
60-70°C honey pasteurises
100°C enzymes break down, honey purified of disease (except AFB) for feeding to same apiary
Heat is used in processing
to make honey easier to strain
to dissolve crystallised honey and reduce subsequent granulation, and
to kill yeasts and thereby prevent fermentation
Honey will degrade over time at elevated temperatures:
o HMF content rises
o Enzyme activity falls
o Volatile oils and hence aroma lost
o Colour darkens
60°C for 45 minutes used to retard crystallisation
60°C for two hours causes noticeable degradation.
70°C used momentarily for “pasteurisation” to reduce yeast content and retard fermentation
Electrical conductivity
- The ability to pass an electric current, usually measured in milli Siemens/cm.
- It is a good indicator of the amount of free acids, proteins and mineral salts in honey.
- It is widely used to distinguish between honeydew and blossom honeys and also to characterise unifloral honeys.
- The conductivity of Blossom honeys should be less than 0.8 mS/cm whilst the conductivity of honeydew and chestnut honeys should be greater than 0.8 mS/cm. But there are exceptions.
- Electrical conductivity is directly related to Ash content and quick method of determining Ash content.
- Conductivity is a good indicator of the botanical origin of honey.
- Determined in routine honey control instead of the ash content.
- Depends on the ash and acid content of honey; the higher their content, the higher the resulting conductivity.
Relative density
Relative Density is the same as specific gravity
The Specific Gravity of a liquid is a dimensionless unit defined as the ratio of density of the liquid to the density of water at a specified temperature.
As the basis it is common to use the density of water at 4°C, the temperature at which it has its highest density (1000 kg/m3).
Varies with sugar content of the honey, so can be used to measure the sugar content.
Varies with temperature, so it should be measured at a stated temperature.
Most conveniently measured using a hydrometer.
Refractive Index
Refractive index is calculated from the angle of refraction (bending) of light as it passes into a material, due to the difference in velocity of light in honey compared to air.
Easily measured with a refractometer.
Refractive Index should be measured at the stated temperature for the most accurate result.
refractive index
Honey, 13% water content 1.504
Honey, 17% water content 1.494
Honey, 21% water content 1.484
