Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Aged distilled spirits such as whiskey are complex mixtures of flavour compounds in an
ethanol-water matrix. The flavour compounds involved can have widely different volatility
and relative amounts. Many of the organoleptic properties that make whiskey suitable for
commercial sale have their origin in reactions occurring during the ageing process in oak
wood barrels.
To investigate the complex changes that take place during spirit ageing a preparative
fractional vacuum distillation process was developed. Both high and low volatility
compounds could be individually isolated as fractions and free from both the ethanol matrix
and the fermentation fusel alcohols. This allowed a range of sensory and analytical
procedures to be conducted on these fractions, in particular to investigate changes occurring
during ageing.
Gas chromatographic (GC) analysis of the low volatility fraction is complicated by the fact
that both the compounds and their ethanol matrix have very similar chromatographic
behaviour when separated simultaneously on standard chromatographic phases. Compound
and matrix co-elution becomes a major problem and conditions for mass spectrometric (MS)
investigation are disadvantageous. A two-dimensional GC configuration using dissimilar
chromatographic phases was configured to overcome these limitations. Using this approach
27 compounds were separated and identified. Headspace injection was used to increase
detection sensitivity. Changes with ageing for seven compounds present at very low levels
were quantified. In addition changes in the most abundant compounds were quantified by
standard split injection, and changes in trace level sulfur compounds by headspace injection
with sulfur chemiluminescent detection (SCD). Increases of the concentrations of pleasant
fruity ethyl esters and acetates were established. Volatile sulfides with generally objectionable
aroma showed concomitant major decreases.
Appropriate techniques could also be applied to the low volatility compounds recovered from
the whiskey water fraction. High temperature GC-MS analysis of an extract of the water
fraction allowed the identification of 30 compounds. Three phenolic esters were identified in
whiskey for the first time. These compounds were synthesised and shown to be contributory
to desirable ageing flavour. Increases in concentrations of 16 oak derived compounds during
alO year ageing period were established. Several compounds increased significantly over
this time period. Ratios of aromatic phenolic aldehydes, and changes in these ratios during
ageing, were unique to the type of barrel used in these experiments. This suggests that the
final sensory properties of aged whiskey may be more dependent on wood parameters than
previously thought.
Preparative reverse phase High Pressure Liquid Chromatography (HPLC) with an ethanol
water gradient was used to further fractionate an extract of the low volatility compounds.
Subsequent analysis and sensory testing allowed a group separation of compounds with each
group contributing characteristic attributes to the total flavour. One group contained the three
new phenolic esters together with a number of other unidentified compounds. This group was
found to be important for desirable ageing flavour that seems to develop slowly with time.
Further studies in this area to understand the individual and synergistic contributions of the
many facets of ageing chemistry will have important commercial implications. / AFRIKAANSE OPSOMMING: Verouderde spiritus soos Whiskey is 'n komplekse mengsel van geurstowwe in 'n etanolwater
oplossing. Die vlugtigheid van die geurstowwe asook die konsentrasies waarin hul
aanwesig is, varieer aansienlik. Verskeie van die sintuiglike eienskappe wat kommersiële
waarde aan whiskey verleen, het huloorsprong in reaksies wat tydens die verouderingsproses
in eikehoutvate plaasvind.
Ten einde die ingewikkelde veranderinge wat tydens die veroudering van spiritus plaasvind,
te ondersoek, is 'n preparatiewe fraksionele vakuumdistillasieproses ontwikkel. Hoogs
vlugtige en minder vlugtige verbindings kon geskei word in afsonderlike fraksies wat vry was
van etanol en fuselalkohole. Dit het die sintuiglike en fisies-chemiese analises van die
fraksies moontlik gemaak, veralom die veranderings wat tydens veroudering plaasvind, te
ondersoek.
Gaschromatografiese (GC) analise van die fraksie met 'n lae vlugtigheid word gekompliseer
deur die feit dat hierdie komponente en die etanol waarin dit opgelos is soortgelyke
chromatografiese eienskappe toon wanneer hul gelyktydig op standaard gaschromatografie
fases geskei word. Die gelyktydige eluering van dié komponente en etanol waarin hul
opgelos is, skep 'n probleem wat nadelig vir massaspektrometriese (MS) analise is. Die
beperkings is oorkom deur die gebruik van tweedimensionele GC en stasionêre fases met
uiteenlopende eienskappe. Op dié wyse is 27 verbindings geskei en geïdentifiseer. Die
veranderinge in konsentrasies tydens veroudering is vir sewe verbindings gekwantifiseer.
Veranderinge in die konsentrasies van die verbindings teenwoordig in die hoogste
konsentrasies is gekwantifiseer deur split-inspuitings, terwyl veranderinge in die spoorkonsentrasies
van vlugtige swawelverbindings mbv dampfase-inspuitings en met swawel
chemolumisensie deteksie (SCD) bepaal is. Toenames in die konsentrasies van die
aangename vrugtige esters en asetate is bepaal. Vlugtige sulfiede met meesalonaanvaarbare
aromas toon gelyktydige groot afnames.
Geskikte tegnieke is ook gebruik vir die herwinning van minder vlugtige verbindings met die
waterfase van whiskey. Hoë temperatuur GC-MS analises van 'n ekstrak van die waterfase
het die identifikasie van 30 komponente moontlik gemaak. Drie fenoliese esters is vir die
eerste keer in whiskey gevind. Hierdie verbindings is gesintetiseer en hul bydrae tot die
gewenste verouderingsgeur is sintuiglik bevestig. Toenames in die konsentrasies van 16
eikehoutverwante verbindings gedurende 'n verouderingsperiode van 10 jaar is bepaal. 'n
Betekenisvolle toename het voorgekom in die konsentrasies van verskeie van hierdie whiskey
verbindings. Die verhoudings van aromatiese fenoliese aldehiede en die verandering in die
verhoudings tydens veroudering was kenmerkend van die tipe eikehoutvat wat gebruik is. Dié
bevinding dui daarop dat die fenole sintuiglike eienskappe van verouderde whiskey meer
afhanklik mag wees van eikehout parameters as wat voorheen algemeen aanvaarbaar is.
Preparatiewe omgekeerde fase hoëdrukvloeistofchromatografie met etanol/water as 'n
gradient elueermiddel is gebruik om 'n ekstrak van die minder vlugtige verbindings verder te
fraksioneer. Verdere GC-, MS- en sintuiglike analise het die skeiding van groepe van
verbindings waarvan elk kenmerkende bydraes tot die totale geur lewer, moontlik gemaak.
Een groep het drie nuut geïdentifiseerde fenoliese esters, tesame met 'n aantal ongeïdentifiseerde
verbindings, bevat. Daar is vasgestel dat hierdie groep 'n belangrike bydrae maak tot
die gewenste geur wat klaarblyklik stadig tydens veroudering ontwikkel. Verdere ondersoeke
in hierdie verband om die individuele en sinergistiese bydraes van verskeie fasette van die
chemie van veroudering te verstaan, kan belangrike kommersiële implikasies hê.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52849 |
| Date | 03 1900 |
| Creators | MacNamara, Kevin |
| Contributors | Van Wyk, C. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 62 pages : illustrations |
| Rights | Stellenbosch University |
Page generated in 0.0021 seconds