**2. Research methods used in the identification of the rheological properties of honey**

Rheological measurements can be conducted using two different measurement techniques: rotational rheometers and capillary rheometers. Due to the speed, comfort of use and the possibility of measurement in wide spectrums of shear rate, rotational rheometers are in popular use at present. The used measurement systems are cone-plate, plate-plate or cylinder-cylinder in a Searle- or Couette-type rheometric flow. Modern-day rheometers are automated and allow obtaining information on the rheological properties relatively quickly, with relatively wide spectrums of shear rate in a precisely planned and repeatable way. The basic problem, which influences the choice of research method significantly, is the presence of the crystallized phase in the case of crystallized honey. The presence of crystals causes significant changes in the rheological properties, which in turn forces a choice of a proper measurement method. A wrong choice of measurement method for crystallized honey can result in unreliable results. As mentioned earlier, crystallized honey is a two-phase mixture, semisolid [5, 14]. It is a popular substance in the food industry. These can be products ready for consumption or half-finished products, which are undergoing processing in the form of solid-liquid mixtures [18]. Crystallized dispersions are also formed by metals in high temperatures. Semisolid media are usually characterized by non-Newtonic properties, and in order to identify them, complex rheological analysis methods are required [18–20].

fluids are described by Newton's law, which may be presented as a linear relation between

 *τ* = *η* ⋅ *γ*˙ . (1) The η parameter in the equation above stands for dynamic viscosity. All fluids, which do not fulfil Newton's law, are called non-Newtonian fluids. Generally, non-Newtonian fluids are divided into rheologically stable, rheologically unstable and viscoelastic. They demonstrate partially viscous, elastic and plastic properties. Rheology is tasked with the description of

The rheological properties of honey are analysed mainly within the aspect of fulfilling the basic production processes such as hydraulic transport, mixing, heating or batching [1]. Viscosity is additionally one of the parameters of quality assessment of the product [2]. In multiple published reports on the rheological properties of honey, there is a common observation that it is in fact a Newtonian fluid [3–6]. A few publications hint at the existence of a clear thixotropic effect, although it is only seen in certain types of honey such as heather honey or the Manuka honey from New Zealand [5, 7]. It needs to be stressed, however, that such reports are with regard to honey in its liquid state also known as strained honey. The parameters, which significantly influence the dynamic viscosity of the analysed product, are

Bee honey is a concentrated aqueous solution of sugars. Due to this, most of the obtained types of honey undergo crystallization when in storage [10]. The crystallization process results directly from the chemical composition, as in almost all types of honey glucose are present in its supersaturated state [5, 11]. Melezitose can also undergo crystallization in honeys. The resulting solid phase is a glucose monohydrate, which has various geometrical forms in crystallization [5, 12, 13]. Honey after crystallization is called set honey and is a two-phase structure, semisolid, which substantially varies in its properties from the liquid state—strained honey [5, 14]. As a result of crystallization, the organoleptic properties undergo significant changes, mainly the honey's texture and water activity [15]. Literature regarding the rheological properties of crystallized honey is surprisingly modest. There are a few studies, which are just starting to analyse the issue [13, 14, 16, 17]. These studies only identify the specific rheological properties of crystallized honeys, as one of the characteristics which change after the crystallization process. This analysis is an attempt at the identification of the rheological properties of honey both in its liquid state and in its crystallized form. The performance of this task has forced an analysis of additional issues, which determine the rheological characteristics. These are the measurement of the amount of solid phase formed after crystallization of the honey and its morpho-

logical characteristics. These issues are relatively seldom analysed in literature [14].

**2. Research methods used in the identification of the rheological** 

Rheological measurements can be conducted using two different measurement techniques: rotational rheometers and capillary rheometers. Due to the speed, comfort of use

shear stress and shear rate:

temperature and water content [5, 8, 9].

**properties of honey**

these properties.

116 Honey Analysis

Research methods regarding liquid and crystallized honeys are characterized below, separately. Additionally research aspects related to measurements of weight fraction and quantity morphological characteristics of the solid (crystallized) phase in crystallized honeys were noted.
