I

ANNO 3 Numero 1
Paola Zucchi [1], Gian Luigi Marcazzan [2], Michele Dal Pozzo [2], Anna Gloria Sabatini [2], Fausto Desalvo [3], Ignazio Floris [4]

Content of ethanol in honey for the assessment of fermentation process

[1] Dipartimento di Scienze degli Alimenti, Università di Bologna, Italy
[2] CRA - Istituto Nazionale di Apicoltura , Bologna, Italy
[3] Dipartimento di Matematica, Università di Bologna, Italy
[4] Dipartimento di Protezione delle Piante - Sez. Entomologia Agraria, Università di Sassari, Italy

Corresponding author: paola.zucchi@unibo.it

The main causes of honey fermentation reported in the literature are water content, expressed as moisture (%) or water activity (aw), bacterial contamination and storage temperatures. At present the determination of whether a honey has undergone fermentation is made by means of a sensory analysis performed by an expert analyst. However, during both production and inspection, it is of fundamental importance to have a parameter and a method of analysis for objectively determining the presence of a fermentation process and defining a threshold for differentiating between fermented and non-fermented honeys.

In this study a procedure for assessing the onset and pattern of fermentation in honeys kept at different temperatures (corresponding to possible and actual storage temperatures) and at different levels of moisture is taken into consideration. The honey chosen for the trial was a spring-summer multiflower honey produced in the plains of Emilia-Romagna, mainly from nectar of lime and ailanthus and from honeydew, and thus characterised by strong aromatic components. The sample was divided into 5 sub-samples, each of which was brought to a defined level of moisture (16, 17, 18, 19, 20%) and submitted both to chemical analysis to determine the baseline content of ethanol, acidity, moisture and aw and to microbiological analysis. Each sample was then further divided into 5 sub-samples, which were stored at different temperatures (15, 20, 25, 30, 35°C) and again submitted to chemical analysis, as well as a sensory analysis to determine the threshold of perceptibility of fermentation. The samples were stored for a total of 18 months.

The findings confirm that the main causes of fermentation in honey are storage temperature and percentage of water; specifically, the critical values were 30°C for temperature and 20% for moisture. It is interesting to note that samples containing 18% moisture stored at 15°C never underwent fermentation and the same applies for samples stored at 35°C (except those containing 20% moisture). It may be assumed, therefore, that this temperature is already sufficient to inhibit the growth of any yeast that might be present.

The importance of the physical state of the honey was also highlighted: conditions that do not lead to fermentation in a liquid honey are by contrast conducive to the phenomenon in honeys as crystallization proceeds, due to the presence of free water molecules.

The results also show that all samples judged by sensory analysis to be at the initial stage of fermentation had an ethanol content ranging from 140 to 160 mg/kg, confirming the threshold values suggested in the literature. This threshold was evaluated for a multiflower honey, but in a honey with more subtle characteristics the threshold of sensory perception may be lower.