Does osmotic distillation change the isotopic relation of wines ?

Currently partial alcohol reduction of wine is in the focus of research worldwide. There are several technologies available to achieve this target. These techniques are either based on distilling or membrane processes. Osmotic distillation, one of the possibilities, is a quite modern membrane process that can be used. During that process, wine is pumped in counter flow to water along a micro porous, hydrophobic membrane. The volatile components of the wine can permeate that membrane and are dissolved in water. The driving force of that process is the vapor pressure difference between the volatiles on the wine and water side of the membrane. The aim of this work was to determine if the alcohol reduction by osmotic distillation can change the isotopic relation in a wine. Can this enological practice change the composition of a wine in a way that an illegal water addition is simulated? Different wines were reduced by 2% alcohol v/v with varying process parameters. The isotopic analysis of the O 16/18 ratio in the wine were performed according to the OIV methods (353/2009) These analyses showed that the isotopic ratio is modified by an alcohol reduction of 2% v/v in a way that corresponds to an addition of 4–5% of external water.


Introduction
Osmotic distillation is a quite new membrane process that is widely used in the beverage industry.It is based on a hydrophobic, micro-porous membrane made out of polyethylene.This membrane can be used in wine industry for gas management.Here you either degas or introduce a selected gas to the wine with that membrane.Another use is the partial alcohol reduction of wine.Here the wine (feed) passes in counter flow to the water (strip) along the membrane.None of the liquids can pass the membrane.The volatiles of the two liquids can pass the membrane by evaporating through its pores.On the other side of the membrane they are then dissolved in the other liquid.Osmotic distillation is an isothermal process at atmospheric pressure.The driving force is the steam pressure difference of a substance between the two sides of the membrane.The volatile components permeate the membrane until an equilibrium arises.The operating pressure is maintained below the capillary penetration pressure of liquids into the pores, the hydrophobic membrane is not wetted by the solutions circulating along the membrane and air gaps are formed into the pores of the membrane [4].There are several synonyms for the process such as: pervaporation, membrane distillation, trans-membrane distillation or capillary distillation [5].
a Matthias.Schmitt@hs-gm.deb marcelo murgo@inv.gov.ar In general the permeation rate of the volatiles can be influenced by several factors.Besides a higher steam pressure difference, higher temperatures and higher flow speed on both sides of the membrane can accelerate the osmotic distillation [17].
In literature there is some proof that during the alcohol removal there is simultaneous water transfer through the membrane.Some factors can promote the water passage.The higher the operating temperature, the higher the water transfer [17].If the water is de-gased before the alcohol removal the water transfer is enhanced [3].When the temperature of the feed is higher than the strip temperature the water also transfers to an higher extend [1].
The amount of water can be up to 3l/m 2 /h [3,17].In case the membrane is leaked due to improper handling the water can flow directly through the membrane.
There are just few information available in what extend the osmotic distillation can change the isotopic relation of a wine, so that an illegal water addition is pretended [1,2].
In this work, wines were treated with different process parameters to evaluate how much this can alter the O 16/18 ratio.Furthermore, aroma and sensory analysis were conducted.

Material and methods
The trials were conducted with two commercial Argentinean wines.A white blend with 80% Sauvignon Blanc 20% Chardonnay with an alcohol content of 13,6% v/v and a red cuvee with 60% Malbec and 40% Sauvignon Blanc that has an alcohol content of 14,0% v/v.The trials, chemical and sensorial analyzes were carried out in the BIO Web of Conferences

Scenario Water/Wine ration with 1% v/v alcohol reduction
Operating temperature The osmotic distillation conducted with the WineBrane Lab Gas/Alc plant from Inoxpa (Banyoles/Spain).Core part of the plant, the membrane contactor is from Liqui-Cel ® (Membrana, Charlote/USA).This membrane contactor was at the time when the trials were conducted 2 years old.The membrane has always been stored and cleaned according to the manufacturer's instructions.An adulteration of the O 16/18 isotopic ratio due to a decline in the hydrophobic habit or a leakage of the membrane can be excluded.
The wine (feed) was pumped by a membrane pump (Flojet, St. Ana/USA) with 300l/h and the water flow (strip) was 120l/h performed by a peristaltic pump (Verder M1500, Haan/Germany).
The trials were carried out with three different scenarios.
The water and the wine were circulated until the alcohol reduction by 2% v/v was reached.
The reagents used are: Carbon dioxide for analysis: SMOW (Standard Mean Ocean Water).

GISP (Greenland Ice Sheet Precipitation). SLAP (Standard Light Arctic Precipitation).
Reference water of own laboratory, carefully contrasted to the reference sample of the International Agency of Atomic Energy in Vienna (IAEA).
Triple manifold for simultaneous recording of ions m/z 44, 45 and 46, or alternatively, a double collector for measuring ions m/z 44 and 46.
Thermostat controlled system (+ 0.5 • C) for equilibration between CO2 and water from wine.
Vacuum pump that can reach an internal pressure of 0.13 Pa.
Sample flasks with a volume of 15 ml and an attached capillary tube having an inner diameter of about 0.015 mm.
Eppendorf pipette with a disposable plastic cone.The aroma analysis was done in Germany at the Hochschule Geisenheim University by the Institute of microbiology and biochemistry according to Rapp et al. 1994.The method was modified by Fischer and Rauhut as follows: Modification of the method: Sample preparation:

Results and discussion
The basic wine parameters except of alcohol and sulphur (e.g. total acidity, malic and tartaric acidity, dry extract, volatile acidity and pH) are not affected by the alcohol reduction by osmotic distillation [7,10] important to check the volatile components of a wine before and after the treatment.
Chart 3 shows the results of the isotopic analysis of the white wine and the red before and after the alcohol reduction by 2% v/v, according to the trial scenarios (chart 2).Furthermore the isotopic ratio of the strip water before and after the treatments, are shown.Besides the 3 scenarios the red wine, was treated severely so that the alcohol reduction was 4,5%v/v.
When comparing the δO18/O16 of the wine before and after the treatment, it gets visible that the alcohol reduction by 2% vol.indicates a water addition to the wine.According to the different scenarios the white wine appears to have 4-5% external water added.The red wine trials indicate 4-9% water addition.The most severe change in δO18/O16 gets visible when the alcohol content is reduced by 4,5% vol.
Contrary to the wine, the strip water shows a lower content of exogenous water after the treatment.This asserts the water transfer from the strip into the feed.
Chart 4 shows the results of the aroma analysis of the white wine.In general the global aroma losses were quite similar for the scenario 1 and 2. The third scenario shows in total slightly lower aroma losses.Most probably this is due to the faster alcohol passage through the membrane, compared to the measured aroma components.This can be explained by ethanol's relatively high steam preassure and the high gradient between feed and strip.
Chart 5 shows the results of the sensory evaluation.There is no significant difference between the white wine control and the different treatments.These results agree with literature [4,8,16] The red wine treated at high temperature and high volumes of strip water shows a significant difference towards the control.This indicates that there is a harming influence of the higher temperature and the high amount of strip water.As expected the alcohol reduction by 4,5% was significantly different from the control.

Conclusion
There are several technologies available to reduce the alcohol.There is just a few sources available how the different physical methods can change the integrity of a wine.There is scientific proof that osmotic distillation can change the isotopic relation of a wine [11,12].This investigation had the aim to check how much osmotic distillation can change the O18/O16 isotopic relation.Can this change already pretend an illegal water addition?Therefore two wines were treated in three different possible scenarios.The scientific theories of literature [3,17] could be proven.The higher the operating temperature and the higher the volume ratio between feed and strip phase, the higher the water passage through the membrane.According to the process parameters the change in O18/O16 isotopic relation was equal to an addition of 4-9% of water.
So far there is no analytical standard for the alcohol reduction by physical methods.
Due to various national restrictions on partial alcohol reduction of wine, there is a need for a reliable proof of the technical intervention to reduce the alcohol content of a wine.
In consequence of various new oenological procedures there is a continuous need to investigate how the integrity of a wine can be influenced.
Chart 3. Change in δO18/O16 due to partial alcohol reduction by osmotic distillation.Initial content and aroma losses of white wine due due different scenarios of alcohol reduction.Results triangle test n = 2 × 7.
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