Technical Bulletin - Interpretation of Heat Stability Results and Turbidity Readings
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TURBIDITY MEASUREMENT
Turbidity is an optical property which causes light to be scattered and absorbed rather than simply transmitted in straight lines through the sample. In a ratio turbidimeter, light is focused and passed through the sample. The 90-degree scatter detector receives light scattered by particles. Transmitted and forward scatter detectors receive light that passes through the sample. A back scatter detector measures light scattered back toward the light source. Results of turbidity measurements are expressed as nephelometric turbidity units (NTU) based upon formazin primary standards.
VISUAL IMPRESSIONS OF TURBIDITY
Typical comparisons of visual impressions to NTU measurements in white wine are given below. The visual impressions are based upon “dark room/perpendicular beam of light” conditions :
HEAT STABILITY TRIALS
Bentonite trials are performed at ETS as follows:
INTERPRETATION OF HEAT STABILITY RESULTS
Formation of haze greater than 1.0 NTU under the conditions of analysis is generally taken to indicate instability. Grossly unstable wines commonly form suspended flocculent masses which prevent precise analysis of turbidity above 5
NTU. Heat stability trial results are presented as NTU values for each of the bentonite fining levels. A pattern is normally observed of decreasing NTU values at increasing levels of bentonite. Clients often choose to accept the bentonite level which corresponds to the “plateau” or level at which NTU values no longer decrease.
(1) Pocock K.F. & B.C. Rankine. “Heat test for detecting protein instability in wine’, Aust. Wine, Brew & Spirit Review (1973)
This document is a compilation of information and views from various sources provided for the convenience of our clients. Information provided in this document is provided "as is" without warranty of any kind, either expressed or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and freedom from infringement. User assumes the entire risk as to the accuracy and the use of this document. This document may be copied and distributed subject to the following conditions: 1) All text must be copied without modification and all pages must be included 2) All copies must contain ETS' copyright notice and any other notices provided therein 3) This document may not be distributed for profit.
All trademarks are acknowledged. Copyright © ETS Laboratories 2001-2010.
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PTB011-Interpretation of Heat Stability Results and Turbidity Readings |
Turbidity is an optical property which causes light to be scattered and absorbed rather than simply transmitted in straight lines through the sample. In a ratio turbidimeter, light is focused and passed through the sample. The 90-degree scatter detector receives light scattered by particles. Transmitted and forward scatter detectors receive light that passes through the sample. A back scatter detector measures light scattered back toward the light source. Results of turbidity measurements are expressed as nephelometric turbidity units (NTU) based upon formazin primary standards.
VISUAL IMPRESSIONS OF TURBIDITY
Typical comparisons of visual impressions to NTU measurements in white wine are given below. The visual impressions are based upon “dark room/perpendicular beam of light” conditions :| NTU | VISUAL IMPRESSION |
| 0 ~ 0.5 | Clear |
| 0.6 ~ 1.0 | Very Light Haze |
| 1.1 ~2.0 | Light Haze |
| 2.0 ~ 3.5 | Hazy |
| 3.5 ~ 5.0 | Very Hazy |
| 5.0 + | Extreme Haze |
HEAT STABILITY TRIALS
Bentonite trials are performed at ETS as follows:
- Samples are fined with bentonite slurry at appropriate levels and settled overnight.
- Samples are filtered using dual glass fiber prefilters and 0.45μm microcellulose membranes into borosilicate glass screw cap tubes.
- Tubes are incubated in a water bath for 6 hours at 80°C and brought to room temperature.
- Turbidity of room temperature samples are read using a Hach ratio turbidimeter.
INTERPRETATION OF HEAT STABILITY RESULTS
Formation of haze greater than 1.0 NTU under the conditions of analysis is generally taken to indicate instability. Grossly unstable wines commonly form suspended flocculent masses which prevent precise analysis of turbidity above 5
NTU. Heat stability trial results are presented as NTU values for each of the bentonite fining levels. A pattern is normally observed of decreasing NTU values at increasing levels of bentonite. Clients often choose to accept the bentonite level which corresponds to the “plateau” or level at which NTU values no longer decrease.
(1) Pocock K.F. & B.C. Rankine. “Heat test for detecting protein instability in wine’, Aust. Wine, Brew & Spirit Review (1973)
This document is a compilation of information and views from various sources provided for the convenience of our clients. Information provided in this document is provided "as is" without warranty of any kind, either expressed or implied, including but not limited to the warranties of merchantability, fitness for a particular purpose and freedom from infringement. User assumes the entire risk as to the accuracy and the use of this document. This document may be copied and distributed subject to the following conditions: 1) All text must be copied without modification and all pages must be included 2) All copies must contain ETS' copyright notice and any other notices provided therein 3) This document may not be distributed for profit.
All trademarks are acknowledged. Copyright © ETS Laboratories 2001-2010.
© 2012 ETS Laboratories. All rights reserved
