Measurement of total soluble solids (TSS) of grapes and must

This document gives a brief summary of the procedures and equipment requirements for some commonly used techniques for determination of TSS of grapes and must. The two most frequently used techniques are hydrometry and refractometry.

Hydrometry

Description: This technique measures the density of the liquid. A glass hydrometer with a suitable scale is floated in a sample of the test liquid that is usually held in a measuring cylinder. Hydrometers can be bought pre-calibrated to a variety of scales including Brix, Balling or Baumé. The measurement is subject to temperature effects and therefore the temperature must be measured and the observed reading corrected using published tables. Such correction tables together with simple conversion tables for converting readings in one scale to another have been published (Amerine and Ough 1980; Rankine 1998).

Equipment: Hydrometer, measuring cylinder, thermometer
Calibration: Pre-calibrated, check with made-up standard solutions of sucrose in water
Services: Wash up area
Space required: Minimal bench space

Refractometry

Description: Refractometers are instruments that measure the refractive index of grape must using the phenomenon of light refraction or of total internal reflection of light. The sugar content of grapes is determined by measuring the refractive index of their juice. The refractometer reading can then be converted to the required units using a standard curve (calibration) based on the concentration of sucrose in sucrose-water solutions. Like hydrometers, refractometers can also be purchased with a variety of scales. The measurement of refractive index is subject to temperature effects and therefore must be corrected for temperature. Most bench-type refractometers, and some hand-held digital types, have automatic temperature compensation. It is also very important that sufficient time be allowed for temperature equilibration of the sample – a common cause of error in many laboratories.

Equipment: Refractometer – hand-held or bench type
Calibration: Use made-up standard solutions of sucrose in water
Services: Wash up area, electricity for bench-type
Space required: Minimal bench space for hand-held, small bench area for bench-type.

Density

Description: Density meters can measure the density of a test liquid with great precision, although the temperature of the sample must be well controlled. A variety of scales are available and most instruments have automatic temperature compensation provided.

Equipment: Density meter
Calibration: Use made-up standard solutions of sucrose in water
Services: Electricity
Space required: Small bench area

References and further reading

  • Amerine, M.A.; Ough, C.S. (1980) Methods for analysis of musts and wines. New York Wiley-Interscience.
  • Iland, P.; Ewart, A.; Sitters, J.; Markides, A.; Bruer, N. (2000) Techniques for chemical analysis and quality monitoring during winemaking. Campbelltown, SA Patrick Iland Wine Promotions.
  • Rankine, B.C. (1998) Making good wine: a manual of winemaking practice for Australia and New Zealand. 1998. South Melbourne, Sun Books (Macmillan Australia).