Charentaise distillation of cognac. Part II: Process simulation and impact of recycling practices on the aroma composition of freshly distilled spirit.

A growing number of studies over the years has successfully employed computer simulation tools to understand, optimize and design spirit distillations. Amongst distilled spirits, cognac is a reputed wine spirit resulting from a double batch distillation process known as Charentaise distillation. This complex operation comprises the wine distillation (WD) and the brouillis distillation (BD), which are carried out in copper alembics. The distillate produced in each batch is fractionated and some of those fractions are recycled in subsequent batches. To improve the current understanding of the behavior of aroma compounds during the process, computer simulation modules were built in this work for a WD and a BD and the results were compared with experimental data. Of the 62 aroma compounds detected in the samples over time, 52 could be represented in the simulations, including 37 using the NRTL thermodynamic model to calculate vapor-liquid equilibria and another 15 with the UNIFAC model. Half of those had their concentration profiles and their partitioning accurately described by the simulation, most of which were modeled with NRTL. This highlights the need for reliable vapor-liquid equilibrium data for aroma compounds that were poorly represented or absent from the simulation as well as kinetic data for chemical reactions occurring during distillation. Furthermore, the impact of the recycling operation on the composition in aroma compounds of freshly distilled cognac was investigated. To represent a steady state, a mathematical model was employed to implement the recycling of distillate fractions during 8 successive Charentaise distillation cycles. The operation was shown to improve the extraction of ethanol and of all volatile compounds in the heart, reaching a pseudo steady state after 3 to 5 cycles. The recycling of the second fraction had a higher influence on the extraction of alcohols and terpenes, while for most esters and norisoprenoids the recycled head fractions played a bigger role.

Charentaise distillation of cognac. Part I: Behavior of aroma compounds.

The Charentaise distillation plays an essential role in designing cognac aroma by extracting and selectively concentrating aroma compounds from the wine along with ethanol, in addition to promoting compound formation or degradation through different chemical reactions. This traditional mode of distillation still relies heavily on empirical knowledge and the impact of its different parameters on the composition of cognac is not fully elucidated. In this context, this study aimed to broaden the current knowledge on the behavior of aroma compounds throughout the two steps of the Charentaise distillation and to investigate the formation of aroma compounds during the operation, an aspect which is seldom considered. The concentration profiles of 62 aroma compounds were represented over time for a wine and a brouillis distillation in usual scale (25 hL) with recycling. A classification system was then proposed to group compounds based on their volatilities at different ethanol concentrations in the boiling liquid, their concentration profiles and their chemical properties. This could help identify how chemical characteristics of aroma compounds affect their volatilities in hydroalcoholic media during distillation. In addition, several compounds appear to be formed during distillation, most of which are terpenes, norisoprenoids and aldehydes. Finally, to highlight the importance of different compounds to the aroma of freshly distilled cognac, their odor activity values (OAV) in the heart fraction were estimated, revealing isobutanol and (E)-ß-damascenone to be the most odorant compounds. These results provided additional elements of understanding for different aspects of the Charentaise distillation for the production of cognac, several of which can be transposed, at least in part, to different modes of distillation pertaining to other distilled beverages.

Adhesion of Bread Dough to Solid Surfaces Under Controlled Heating: Balance Between the Rheological and Interfacial Properties of Dough.

The adhesion of wheat dough affects many aspects of industrial baking, from kneading raw dough to the final baking process. In this work, an original method was developed to study the effect of temperature on the adhesive properties of bread dough in contact with a solid surface during heating. Using this approach, it will be possible to understand the factors that affect adhesion between dough and a baking surface, which will aid in developing methods to prevent dough from sticking. Overall, the dough's adhesion to a hydrophobic surface globally decreased with an increase in temperature from 35 to 97 °C, with the exception of the temperature range between 55 and 70 °C, in which the energy of adhesion increased slightly. Under these circumstances, the evolution of adhesion was primarily shaped by the rheological properties of the dough. However, when we used a solid surface with different surface energy, the results changed significantly, which suggests that the mechanisms of adhesion during heating are governed by a balance between the interfacial and bulk properties of the heated dough. The overall decrease in the adhesion of the dough to the hydrophobic glass surface may be explained by a decrease in dough hydrophobicity due to structural and chemical changes in the dough.

Evolution of Volatile Compounds during the Distillation of Cognac Spirit.

Cognac wine spirit has a complex composition in volatile compounds which contributes to its organoleptic profile. This work focused on the batch distillation process and, in particular, on volatile compounds specifically produced by chemical reactions during the distillation of Cognac wine spirit, traditionally conducted in two steps with charentais pot stills. The aim of this study was to characterize these volatile compounds formed during distillation. Sampling has been performed on the distillates and inside the boiler during a typical Cognac distillation. The analysis of these samples allowed us to perform a mass balance and to point out several types of volatile compounds whose quantities strongly increased during the distillation process. These compounds were distinguished by their chemical family. It has been found that the first distillation step was decisive for the formation of volatile compounds. Moreover, 2 esters, 3 aldehydes, 12 norisoprenoids, and 3 terpenes were shown to be generated during the process. These results suggest that some volatile compounds found in Cognac spirit are formed during distillation due to chemical reactions induced by high temperature. These findings give important indications to professional distillers in order to enhance the product's quality.

Furan quantification in bread crust: development of a simple and sensitive method using headspace-trap GC-MS.

To study reactivity in bread crust during the baking process in the pan, we followed furan mainly resulting from Maillard and caramelisation reactions in cereal products. Furan quantification is commonly performed with automatic HS-static GC-MS. However, we showed that the automatic HS-trap GC-MS method can improve the sensitivity of the furan quantification. Indeed, this method allowed the LOD to be decreased from 0.3 ng g(-1) with HS-static mode to 0.03 ng g(-1) with HS-trap mode under these conditions. After validation of this method for furan quantification in bread crust, a difference between the crust extracted from the bottom and from the sides of the bread was evident. The quantity of furan in the bottom crust was five times lower than in the side crust, revealing less reactivity on the bottom than on the sides of the bread during the baking process in the pan. Differences in water content may explain these variations in reactivity.

Lipid oxidation in baked products: impact of formula and process on the generation of volatile compounds.

This paper investigates the effect of ingredients on the reactions occurring during the making of sponge cake and leading to the generation of volatile compounds related to flavour quality. To obtain systems sensitive to lipid oxidation (LO), a formulation design was applied varying the composition of fatty matter and eggs. Oxidation of polyunsaturated fatty acids (PUFA) and formation of related volatile compounds were followed at the different steps of cake-making. Optimised dynamic Solid Phase Micro Extraction was applied to selectively extract either volatile or semi-volatile compounds directly from the baking vapours. We show for the first time that in the case of alveolar baked products, lipid oxidation occurs very early during the step of dough preparation and to a minor extent during the baking process. The generation of lipid oxidation compounds depends on PUFA content and on the presence of endogenous antioxidants in the raw matter. Egg yolk seemed to play a double role on reactivity: protecting unsaturated lipids from oxidation and being necessary to generate a broad class of compounds of the Maillard reaction during baking and linked to the typical flavour of sponge cake.

Use of inverse gas chromatography to determine thermodynamic parameters of aroma-starch interactions.

Interactions between aroma compounds (d-limonene, ethyl hexanoate, octanal and 1-hexanol) and high amylose cornstarch were studied using inverse gas chromatography. Free energies of adsorption (deltaGa) and enthalpies of adsorption (deltaHa) of aroma compounds on starch were measured in the temperature range of 33-40 degrees C. The results showed existence of interactions between aroma compounds and starch, involving hydrogen bounds and dipole-dipole interactions. Sorption isotherms and Henry's law solubility coefficients (S) were determined at 40 degrees C. Three different shapes of isotherms were obtained according to the BET classification: type III for d-limonene, type II for ethyl hexanoate and linear for octanal and 1-hexanol.