Search: thermal stress

The thiobarbituric acid index is a measure of the cumulative thermal stress brought about by exposure to heat (intensity) in malt and wort. The TBI is a figure, which indicates the presence of numerous Maillard reaction products in addition to 5-hydroxymethylfurfural (HMF) and other organic compounds.

The analysis sample (e.g., wort, beer or wort obtained from a standardized method, such as Congress wort) undergoes a chemical reaction with an acetic acid/thiobarbituric acid solution; the resulting product is yellow in color and is measured spectrophotometrically.

5-Hydroxymethylfurfural (HMF) is separated using HPLC and reversed phases. This substance is measured with a UV detector.
HPLC analysis specifically detects 5-hydroxymethylfurfural.

A photometric method, B-590.59.111 Hydroxymethylfurfural - photometrisch, using barbituric acid and o-toluidine detects all aldehydes present in the sample. This method serves as an alternative for laboratories without HPLC.

The time required to develop a product – from conception to launch on the market – is steadily shrinking. Since recipes are also becoming ever more complex and a wide range of different types of packaging are now employed, forced stability tests have become absolutely essential, in order to establish a realistic indication of a product’s shelf-life.

Inferences about the shelf-life of a product can only be made if the entire beverage concept is taken into consideration, such as the recipe, filling technology, packaging and distribution.

The most important stress factors in the aging process are heat, light and oxygen.

PET bottles have become a popular form of packaging for non-alcoholic beverages, and their permeability to gas, most especially oxygen, is therefore a critical parameter in the aging process.

The testing process described below operates, of course, on the assumption that the chemical reactions in the aging process are subject to the same mechanisms, whether they occur at temperatures typical for beverage storage or at somewhat elevated temperatures, and that they follow a linear relationship dependent on temperature. The same applies to forced photochemical reactions and to reactions brought about by an increase in the partial pressure of oxygen on the beverage. To verify results from forced testing, they can be compared and correlated to results from real-time tests on the same product. 

5-Hydroxymethylfurfural (HMF) is detected in a color reaction with barbituric acid and o-toluidine. However, this detects all of the aldehydes present in the sample. The determination by HPLC specifically detects the HMF. As with other aldehydes, HMF reacts with barbituric acid and p-toluidine to create a reddish compound. HMF reacts with any sulfurous acid that is present, as do other aldehydes; in this case, it is, therefore, undetectable without prior treatment. If more than 10 mg/l of free sulfurous acid are present, this will bind to acetaldehyde. Subsequently, the determination can be performed. The presence of excess acetaldehyde does not interfere with the analysis.

The extract content of malt refers to the compounds from finely ground malt (fine grind), which are brought into solution during a standardized mashing process.

The extract content is determined by the weight ratio sL 20/20 of the wort on the basis of the official sugar tables (Plato tables) at 20 °C. sL 20/20 stands for the weight ratio of a volume of wort at 20 °C to the same volume of water at the same temperature. 

The time from the beginning to the end of filtration is determined when producing a laboratory mash.