Thesis (MScAgric)--Stellenbosch University, 2022.ENGLISH ABSTRACT: The removal of dissolved oxygen through desorption is commonly done in winemaking.
Winemakers have indicated that under the same conditions, this process takes place at different
rates, for different wines. The mass transfer of oxygen in six wines and various model wine
solutions, was examined by evaluating the oxygen desorption volumetric mass transfer coefficient
( ), the Sauter mean bubble diameter (D32), gas holdup (), the interfacial area (), and the
oxygen mass transfer coefficient (). One of the wines used was split into two batches, with one
half treated with bentonite, and the other not. A bubble column with a stone sparger was used for
the experiments. The gassing out procedure and a 2nd order model was used to determine .
Bubble imaging was done to determine the interfacial area, and subsequently the .
During oxygen desorption within wine, the values varied between 0.0125 s-1 and 0.0275 s-1
depending on the wine. The value during oxygen desorption within a 10 % ethanol solution
was found to be 0.0275 s1. The addition of a small amount glycerol to this system reduced the
to 0.0225 s-1. Further additions of organic acids did not affect the , while the addition of
protein in the form of BSA and yeast extract reduced the to approximately 0.0175 s-1. The
for during oxygen desorption within a wine that was protein unstable improved from 0.009 s1 to
0.015 s1 after being treated with bentonite.
During desorption, there were no significant variations in the D32 and the interfacial area between
systems containing wines or model wine solutions. Consequently, the variations between the
values could all be ascribed to differences in the . During oxygen desorption, the values
were found to be between 0.015 and 0.045 mm/s within the different wines. The values were
found to be between 0.03 and 0.04 mm/s within a 10% ethanol solution, and within the model
wine solutions containing glycerol and organic acids. The values dropped between 0.02 and
0.03 mm/s with the addition of protein to the model wine solution. Treating a protein unstable wine
with bentonite increased the value from 0.017 mm/s to 0.0225 mm/s.
The combination of the reduction in the when protein was added to a model wine solution, and
the improvement of the when wine was treated with bentonite, suggested that proteins in wine
significantly affect oxygen desorption rates. It is suggested that winemakers can improve the
oxygen within their system by operating at higher gas flowrates to increase the turbulence
during desorption. However, the most effective way of improving the desorption rate is by using
a sparger that produces smaller bubbles, so as to increase the interfacial area. It is suggested
that desorption is performed after fining, as the will be greater.AFRIKAANSE OPSOMMING: Die verwydering van opgeloste suurstof deur middel van desorpsie kom algemeen in
wynbereiding voor. Wynmakers het aangedui dat, onder dieselfde toestande, hierdie proses teen
verskillende tempo’s vir verskillende wyne plaasvind. Die massa-oordrag van suurstof in ses wyne
en verskillende model-wynoplossings is ondersoek deur die volumetriese massa-
oordragkoëffisiënt ( ) van suurstof desorpsie, die Sauter gemiddelde borreldeursnee (D32),
gasvertraging (gas holdup) (), die oppervlakte van die koppelvlak () en die suurstof massa-
oordragkoëffisiënt () te evalueer. Een van die wyne wat gebruik is, is in twee verdeel, die een
helfte waarvan met bentoniet behandel is en die ander nie. ’n Borrelkolom met ’n klip
sprinkeltoestel (stone sparger) is vir die eksperimente gebruik. Die ontgassingsprosedure
(gassing out) en ’n tweede-orde model is gebruik om te bepaal. Borrel beelding (imaging) is
gedoen om die oppervlakte van die koppelvlak, en gevolglik die , te bepaal.
Tydens suurstofdesorpsie in die wyn het die -waardes tussen 0.0125 s-1 en 0.0275 s-1
gewissel, afhangend van die wyn. Die -waarde tydens suurstofdesorpsie met ’n 10%
etanoloplossing was 0.0275 s1. Die toevoeging van ’n klein hoeveelheid gliserol aan hierdie
stelsel het die tot 0.0225 s-1 verminder. Verdere toevoegings van organiese sure het nie die
geaffekteer nie, terwyl die toevoeging van proteïen in die vorm van BSA en gis-ekstrak die
tot ongeveer 0.0175 s-1 verminder het. Die tydens suurstofdesorpsie in ’n wyn wat
proteïen-onstabiel was, het verbeter van 0.009 s1 tot 0.015 s1 ná behandeling met bentoniet.
Tydens desorpsie was daar geen betekenisvolle verandering in die D32 en in die oppervlakte van
die koppelvlak tussen stelsels wat wyn of model-wynoplossings bevat het nie. Gevolglik kon die
verskille in die -waardes almal aan verskille in die toegeskryf word. Tydens
suurstofdesorpsie was die -waardes in die verskillende wyne tussen 0.015 en 0.045 mm/s. Die
-waardes was tussen 0.03 en 0.04 mm/s in ’n 10% etanoloplossing, asook in die model-
wynoplossings wat gliserol en organiese sure bevat het. Die -waardes het met tussen 0.02 en
0.03 mm/s gedaal met die toevoeging van proteïen aan die model-wynoplossing. Die behandeling
van ’n wyn wat proteïen-onstabiel was met bentoniet het die -waarde van 0.017 mm/s tot 0.0225
mm/s verhoog.
Die kombinasie van die afname van die toe proteïen by ’n model-wynoplossing gevoeg is en
die verbetering van die toe die wyn met bentoniet behandel is, suggereer dat proteïene in wyn
die suurstofdesorpsie-tempo’s aansienlik beïnvloed. Daar word voorgestel dat wynmakers die
suurstof- in hulle stelsel kan verbeter deur teen hoër gasvloeitempo’s te werk om die turbulensie
tydens desorpsie te verhoog. Die doeltreffendste manier om die desorpsietempo te verbeter, is
egter om ’n sprinkeltoestel te gebruik wat kleiner borrels produseer om sodoende die oppervlakte
van die koppelvlak te vergroot. Daar word ook voorgestel dat desorpsie ná brei uitgevoer word,
aangesien die groter sal wees
