Understanding Density, Viscosity, and Organoleptic Testing
Absolute density is the ratio of the mass of a body to its volume. Relative density is the density of a substance (d2) with respect to the density of a reference substance (d1).
Factors Affecting Measurement Systems
The measurement system depends on different factors:
- The nature of the liquid
- The amount of liquid available
- The viscosity of the liquid
- The purpose for which density is determined
- The accuracy required in the measurement
Alcoholmeters
Alcoholmeters are used to determine the concentration of aqueous ethyl alcohol solutions. They are calibrated at 20ºC and are commonly used in alcoholic beverages.
Brix Aerometer
A Brix aerometer is a graduated instrument that corresponds to the percentage of sugar (sucrose) at the calibration temperature.
Baumé Aerometer
A Baumé aerometer is an instrument for measuring liquid densities, similar to a densimeter. The difference lies in the measurement scale, which is used to determine the sugar content of wine must.
Viscosity
Viscosity is a measure of a fluid’s resistance to flow within a channel, resulting from the cohesion and adhesion of its molecules when a shear force is applied. Its main cause is the internal friction of the molecules.
Absolute or Dynamic Viscosity
Absolute or dynamic viscosity is mathematically defined as the force per unit area (shear stress) required to displace particles of the liquid with a certain velocity gradient.
Relative or Kinematic Viscosity (η)
Relative or kinematic viscosity (η) is defined as the relationship between the absolute viscosity of the fluid and its density at the same temperature.
Fluid Characteristics
A fluid is a continuous medium whose mass adapts to the container holding it. Its molecules are bound together by weak forces of attraction, and due to this poor molecular cohesion, they have the ability to flow, that is, move without retaining its shape.
Newtonian Fluids
Newtonian fluids are those in which the internal stresses of the fluid, when applying a force, are proportional to the velocity of the fluid, resulting in a linear relationship between the cutting effort and deformation speed.
Non-Newtonian Fluids
Non-Newtonian fluids are those in which the internal stresses of the fluid, when applying a force, are not proportional to the velocity of the fluid, meaning the ratio of shear stress and the deformation rate is not linear.
Organoleptic Tests
Organoleptic tests are those that refer to both the external appearance of matter and the sensations it produces. There are assays that can be performed by laboratory analysts on instrumentalized equipment, or there are sensory-type attributes that will be performed in panel-type tests.
Appearance
Appearance is the external look of a substance, mainly the description of its state, texture, and color.
Texture
Texture refers primarily to the superficial appearance of the substance, describing a visual attribute of a solid, semi-solid, or emulsion.
Turbidity
Turbidity is the reduction of the transparency of a liquid due to the presence of undissolved particles of material other than the liquid itself.
Color
Color is the visual sensation that originates from the stimulation of the retina, within the human eye’s range of 380 to 750 nm.
Parameters of Color
- Clarity or Luminosity: It’s the amount of light and is the physical appearance of the color attribute which is associated with the luminance of the object.
- Tone: Tone is the attribute that indicates color and is the physical aspect related to the dominant wavelength.
- Saturation: Saturation is the attribute that indicates the relationship between white and pure spectral color, being the inverse of the proportion of white.
Nessler Tubes
Nessler tubes are used to determine the color of solutions. They are test tubes with a flat bottom and wider shape, with a capacity of 50 or 100 mL and a high form, although they may also be low, more suitable for dark solutions.
Colorimeters
Colorimeters are equipment based on the numerical determination of color by measuring the spectral reflectance of a sample.
Spectrophotometer
A spectrophotometer is used for measuring the intensity of light transmitted through a sample.
Taste
Taste is the sensation or impression caused by a substance in the taste buds of the tongue and palate, accompanied by the smell they produce. There are five basic flavors: sweet, salty, bitter, sour, and umami.
- Discrimination Tests: These tests consist of comparing two or more samples and determining if there are any differences.
- Descriptive Tests: These tests allow you to know the characteristics of the product or to assign some attributes such as size, color, etc., or to perform description tests such as taste and texture.
- Affective Tests: These are tests that express the degree or level of acceptance, pleasure, or preference.