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The influence of base wine composition and wood maturation on the quality of South African brandySnyman, Caroline Lucie Charlotte 03 1900 (has links)
Dissertation (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Brandy production is a multi-step process that involves grape harvesting, base wine
fermentation, distillation, wood maturation and blending. Within each of these production
process steps there are a number of factors that can influence the composition and
resultant quality of the base wine, unaged and wood matured distillates. These factors
include geographic and climatic features of the origin of grapes used, viticultural practices,
grape maturity, grape variety, vintage variation, vinification techniques, storage of the base
wine prior to distillation, distillation technique, age and origin of oak wood used for
maturation and barrel toasting levels.
The composition of flavour is extremely complex in wine and distilled beverages such
as brandy. A multitude of compounds can take part in the formation of flavour, and it is
rare that a particular compound, that is solely responsible for nuances of a specific flavour,
is identified. Thus, taking brandy production factors and the nature of aroma and flavour
into account, it is clear that thorough understanding of the complexities affecting the
perception of quality in brandy is difficult.
In commercial brandy production, standard operating procedures do not allow for the
separate distillation of brandy base wines from different producers and mixing of base
wines from different regions and producers thus occurs. This makes it difficult to determine
whether the quality determination of the base wine is in fact an indication of the quality of
the resultant distillate after the required period of wood maturation. Therefore, the aim of
this study is to determine whether there is any merit in storing and distilling brandy base
wines from different producers and regions separately. This was done by firstly
determining the demographic and production factors that influence brandy base wine
composition. Secondly, the influence of brandy base wine composition on the quality of the
respective unaged potstill distillates as well as the ultimate style and quality of the threeyear
old wood matured potstill distillates was determined.
For this purpose, four potstills with a capacity of 2000 L each were isolated and used
for commercial scale distillations of 33 and 25 brandy base wines in 1999 and 2000,
respectively, at the DisteIl distillery in Worcester. The experimental outlay used in the
study closely emulated Distell's standard operating procedures for commercial brandy
production.
Chenin blanc and Colombar are the two most popular grape varietals used in the
making of brandy base wine in South Africa. Due to the complexity of the brandy
production process, the first part of the study only focussed on South African young
Chenin blanc wines, with a predominantly fermentation derived aroma. The concentration
of iso-amyl acetate, hexyl acetate, ethyl caprylate, ethyl caprate, 2-phenethyl acetate and
octanoic acid was significantly higher in wines awarded gold and silver medals and
decreased significantly with subsequent decreases in quality categories. Ethyl lactate
exhibited the opposite pattern. A quality predictor model based on the behaviour of 21 volatile compounds quantified in these wines had a resonable prediction accuracy when
having to predict the quality of wines made in the same vintages as it had been trained on.
It was significantly poorer when tested on a completely different vintage of wines to the
ones it had been trained on. The number of vintages, number of wines per vintage and the
number of compounds quantified for the model influence its prediction accuracy.
Twenty-seven volatile compounds were quantified in 33 and 25 brandy base wines,
their unaged and three year old distillates from 1999 and 2000, respectively. ANOVA and
CART analysis showed that vintage, region, harvest time, choice of cultivar and yeast
strain can have a significant influence on the volatile compound composition of brandy
base wines, their unaged and three year old distillates. These factors as well as the
volatile compound composition were also found to influence the sensory quality of these
products. Base wines, unaged and three year old distillates originating from the De Dooms
region, which predominantly cultivates table grapes, were of significantly lower quality than
those from the remaining regions. Products made from grapes harvested early in the
season were of significantly higher quality. The volatile aroma compound composition was
found to differ significantly between the 1999 and 2000 base wines and distillates,
irrespective of the exclusion of those samples that had undergone partial or complete
malolactic fermentation. Consequently, quality indicating compounds may vary from
vintage to vintage. The relationship between the quality of brandy base wines and the
concentration of n-butanol, iso-amyl acetate, ethyl lactate, ethyl caprylate, octanoic- and
decanoic acid was the same as that reported in young Chen in blanc wines in this study. In
unaged distillates, increased levels of ethyl lactate also exert a negative influence on
distillate quality. Iso-amyl acetate, hexyl acetate, ethyl caproate, ethyl caprylate, n-butanol,
octanoic acid, ethyl caprate and decanoic acid showed some positive correlation, whilst
iso-butanol, ethyl lactate, acetic acid, acetaldehyde and ethyl acetate showed a significant
negative correlation to three-year old distillate quality.
Sensory descriptive analysis on selected good, average and poor quality distillates
using the South African brandy aroma wheel showed that there are small differences in
profile between the good and average distillates, there were however significant
differences between the good and poor quality distillate profiles throughout maturation.
After three years of wood maturation, the aroma profile of poor quality distillates can be
characterised by prominent herbaceous and woody aromas, which are more intense than
the fruity aromas. Good quality distillates contained characteristically intense fruity aromas.
Volatile compound concentration differences were noted during the course of and after
three years of wood maturation and in barrels of varying ages. Distillates matured in new
block barrels exhibited significant differences in volatile and wood compound composition
after three years when compared to remaining barrels used. The style classification of the
three-year old potstill distillate was influenced by demographic and production factors and
volatile compound composition, but not by the sensory quality of the distillates.
In summary, vintage, region, cultivar, harvest time and choice of yeast strain have a
significant influence on the volatile composition of brandy base wines, their unaged and three year old potstill distillates, which in turn affects the sensory quality of these products.
These effects cannot be viewed in isolation as they jointly exert an influence on the
composition and quality of these products. From a commercial perspective, this study has
provided a valuable indication as to which production and demographic factors can
influence the quality and style of potstill brandy. Thus, future brandy base wine intake
should, as far as possible, take place in such a manner to allow base wines originating
from the same cultivar or region or harvest time or combination thereof (and to a lesser
extent yeast strain) to be received simultaneously at the distillery for distillation. / AFRIKAANSE OPSOMMING: Brandewyn produksie is 'n veelvoudige proses wat die volgende insluit: pars van druiwe,
basiswyn fermentasie, verstoking, houtveroudering en versnyding. Binne hierdie stappe is
verskeie faktore wat 'n invloed op die samestelling en resultate van die basiswyn,
onverouderde en verouderde distillaat kan hê. Hierdie faktore sluit die volgende in:
geografiese ligging, klimaat toestande van die streek van herkoms, wingerdboupraktyke,
graad van rypheid, druifvarieteit, wynoes variasie, wynbou tegnieke, opberging van
basiswyn voor distillasie, distillasie tegnieke, ouderdom en oorsprong van akkerhout vir die
veroudering, asook tot watter mate die vat gerooster is.
Die samestelling van geur in wyn en gedistilleerde produkte soos brandewyn is uiters
kompleks. 'n Menigte samestellings kan deel vorm van die inhoud van die geur, en dit is
raar dat 'n bepaalde verbinding alleenlik verantwoordelik is vir 'n kenmerkende geur.
Weens die verskeidenheid van produksie faktore, aroma en smaak is volledige kennis van
brandewyn ingewikkeld en kompliseerd om te verstaan.
In kommersiële brandewynproduksie, maak standaard werksprosedures nie
voorsiening vir aparte distillasie van basiswyn van verskillende produsente nie, en die
vermenging van basiswyn van verskillende streke en produsente kom voor. Dit maak dit
moeilik om te bepaal of die kwaliteit van die basiswyn of die distillaat na die neergelegde
periode van houtveroudering, in werklikheid 'n beslissende indikasie op die kwaliteit van
die verouderde produk is. Daarom is een van die doele van hierdie studie om te bepaal of
daar meriete in is om brandewyn basiswyn van die verskillende produsente en streke
apart te berg en te verstook. Dit is gedoen deur eerstens, die effek van demografiese en
produksie faktore op die samestelling van brandewyn basiswyn te bepaal. Daarna, om die
invloed van brandewyn basiswynsamestelling op die kwaliteit van onderskeidelik die
onverouderde distillate sowel as die uiteindelike styl en kwaliteit van die 3 jaar oue
houtverouderde potketel distillate, te bepaal.
Vir hierdie doel, is vier potketels met 'n kapasiteit van 2000 liters elk geïsoleer en vir
kommersiële skaal distillasies van 33 en 25 brandewyn basiswyne in 1999 en 2000,
ondeskeidelik, by DisteIl Distillerdery, Worcester verstook. Die eksperimentele uitleg wat
in hierdie studie gebruik is, ewenaar DisteIl se standaard verstokingsprosedures vir
kommersiële brandewynproduksie.
Chenin blanc en Colombar is die twee mees populêre druifvarieteite vir die maak van
brandewyn basiswyn in Suid-Afrika. As gevolg van die kompleksiteit van die brandewyn
produksieproses, is die eerste gedeelte van die studie gefokus op die Suid-Afrikaanse jong
Chenin blanc wyne, met 'n oorheersende fermentasie geur. Die konsentrasie van iso-amyl
asetaat, heksiel asetaat, etiel kaprilaat, etiel kapraat, 2-phenetiel asetaat en oktanoë suur
was aansienlik hoër in wyne wat met goud en silwer medaljes bekroon is en neem
aansienlik af met afname in kwaliteit kategorieë. Etiel laktaat vertoon die teenoorgestelde
patroon. 'n Kwaliteit voorspellersmodel, gebaseer op die gedrag van 21 vlugtige komponente was opgestel. Die model het redelike akkuraatheid getoon op wyne van
dieselfde oesjaar as waarop oorspronklik opgelei. Die model se voorspellingsakkuraatheid
was aansienlik swakker toe dit vergelyk getoets is met wyne van 'n nuwe oesjaar. Die
hoeveelheid oesjare, hoeveelheid wyne per oesjaar en die hoeveelheid verbindings
gebruik in hierdie model sal die voorspellingsakkuraatheid beïnvloed.
Sewe-en-twintig vlugtige komponente was gekwantifiseer in 33 en 25 brandewyn
basiswyne, die onverouderde en 3 jaar oue distillate vanaf 1999 en 2000, onderskeidelik.
Variasie ontledings (ANOVA) en klassifikasie en regressie ontledings (CART) ontledings
wys dat oesjaar, streek, parstyd, keuse van kultivar en gisrasse In aansienlike invloed op
die vlugtige samestelling van brandewyn basiswyne asook hul onverouderde en 3 jaar
distillate het. Hierdie faktore, sowel as die vlugtige verbinding samestellings, beinvloed
ook bevind die sensoriese kwaliteit van hierdie produkte. Basiswyne, onverouderde en 3
jaar oue distillate wat vanuit die De Doorns streek, wat hoofsaaklik tafeldruif kultivars is, is
van In swakker kwaliteit as die ander streke. Produkte wat gemaak is van druiwe wat
vroeg in die seisoen gepars is, was van beter kwaliteit. Die vlugtige
geurkomponentsamestellings het tussen die basiswyne en distillate van die 1999 en 2000
oesjare verskil, ongeag of party van die monsters gedeeltelike of volledige
appelmelksuurgisting ondergaan het. Gevolglik, die konsentrasie van kwaliteitaanwysende
komponente mag van seisoen tot seisoen verskil. Die verhouding tussen die kwaliteit van
die brandewyn basiswyne en die konsentrasie van n-butanol, iso-amiel asetaat, etiel
laktaat, etiel kaprilaat, oktanoë- en dekanoë suur was dieselfde soos gerapporteer oor die
jong Chenin blanc wyne. In onverouderde distillate, het verhoogde vlakke van etiel
laktaat In negatiewe invloed op distillaat kwaliteit veroorsaak. Iso-amiel asetaat, heksiel
asetaat, etiel kaproaat, etiel kaprilaat, n-butanol, oktanoë suur, etiel kapraat en dekanoë
suur In positiewe korrelasie, terwyl iso-butanol, etiel laktaat, asynsuur, asetaldehied en
etiel asetaat betekenisvolle negatiewe korrelasie met 3jaar oue distillaat kwaliteit bewys.
Beskrywende sensoriewe analises op geselekteerde, middelmatige en swak kwaliteit
distillate (gedoen deur gebruik making van die Suid-Afrikaanse Brandewyn Aromawiel)
wys dat daar klein verskille tussen die profiele van goeie en middelmatige distillate is.
Daar is egter aansienlike verskille tussen goeie en swak kwaliteit distillataat profiele
regdeur die drie jaar verouderingsperiode. Na 3 jaar van houtveroudering kan die geur
profiel van swak kwaliteit distillate uitgeken word aan kruid- en houtagtige geure, wat meer
intens as die vrugagtige geure is. Goeie kwaliteit distillate het intense vrugagtige-aroma
eienskappe.
Vlugtige verbinding konsentrasie verskille is waargeneem gedurende en na die 3jaar
houtverouderingsperiode in vate wat van ouderdomme verskil. Distillate wat in nuwe
blokkies vate verouder is, vertoon aansienlike verskille in vlugtige en houtkomponent
samestellings na 3 jaar wanneer dit met die, wat in die oorblywende ouer vate verouder is,
vergelyk word. Die styl klassifikasie van die 3 jaar oue potketeldistillaat was deur
demografiese en produksie faktore sowel as vlugtige verbinding samestellings beïnvloed,
maar nie met die sensoriese kwaliteit van die distillate nie. In opsomming, oesjaar, streek, kultivar, parstyd en keuse van gisrasse het 'n
aansienlike invloed op die vlugtige komponent samestelling van die brandewyn basiswyne,
onverouderde en 3 jaar oue potketel distillate, wat weer op hul beurt die sensoriese
kwaliteit van die onderskeidelike produkte beïnvloed. Die effek van hierdie faktore kan nie
in isolasie gemeet word nie, aangesien dit gesamentlik die kwaliteit van die produkte
beïnvloed. Van 'n kommersiële perspektief het hierdie studie 'n waardevolle indikasie
gelewer van hoe produksie en demografiese faktore die kwaliteit en styl van
potketelbrandewyn kan beïnvloed. Daarom word voorgestel dat toekomstige brandewyn
basiswyn innames, sover as moontlik, voorsiening moet maak om wyne van dieselfde
kultivar, uit dieselfde streek, parsseisoen inaggeneem, of kombinasie daarvan, met 'n
mindermate die gisrasse in aanmerking geneem, gelyktydig vir verstoking by die
distilleerderye ontvang word sodat hierdie wyne apart van wyne met ander bogenoemde
variasies verstook en verouder kan word.
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A qualitative and quantitative determination of the amino acids and aroma substances, especially esters, aldehydes and ketones in musts and winesVenter, P. J. (Peter Jacobus) 12 1900 (has links)
Thesis (DScAgric)--Stellenbosch University, 1958. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming
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The impact of nutrients on aroma and flavour production during wine fermentationSmit, Anita Yolandi 03 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: During wine fermentation, numerous grape must constituents serve as nutrients to wine yeast
(Saccharomyces cerevisiae), which enable their growth and successful completion of alcoholic
fermentation. Many of these nutritional factors, in particular nitrogen, also act as precursors for yeastderived
flavour compounds such as higher alcohols, esters and volatile fatty acids. Yeast nitrogen
metabolism thus plays a determining role in wine aroma and quality. Not only is the nitrogen source,
concentration and supplementation timing important, but various environmental factors and the genetic
constitution of the yeast strain used for fermentation will also contribute to fermentation outcomes.
The main goal of this work was to explore the complex interactions between a number of contributing
factors; namely nitrogen source, timing of addition, yeast strain and fermentation matrix. Broadly, this
study assessed the impact of seven different nitrogen combinations, added either to the initial grape must
or after the onset of fermentation, on fermentation performance and aroma compound production by nine
commercial wine yeast strains. Fermentations were done in synthetic grape must, and validated for a
subset of parameters in real grape must. The nitrogen treatments were designed according to the generally
established order of preference of S. cerevisiae for individual amino acids as source of nitrogen under
fermentative conditions, and the potential of certain amino acids to participate in metabolic pathways that
produce specific aroma compounds.
The results reveal that different nitrogen combinations can lead to unexpected aroma outcomes,
depending strongly on the genetic background of individual yeast strains and the timing of nitrogen
addition. Certain nitrogen treatments consistently resulted in significant increases or decreases in specific
aroma compound concentrations in comparison to the treatment fermented on ammonium as only
nitrogen source, for multiple yeast strains. These compounds were classified as nitrogen treatment
dependent. Other aroma compounds were produced similarly for all nitrogen treatments and were
designated as nitrogen treatment independent. The presence of specific amino acid groups (for example
the branched-chain and aromatic amino acids) could be correlated to significantly altered production
patterns of related (such as higher alcohols) or unrelated (diethyl succinate) aroma compounds relative to
the other nitrogen treatments. Taken together, a number of interesting and novel hypotheses regarding the
metabolic pathways involved could be derived from the data.
Ultimately, this initial assessment of interactive effects during fermentation will contribute to practical
guidelines for winemakers to allow matching grape must constituents (such as nutrients) with the intrinsic
aroma production capabilities of specific yeast strains in order to modulate wine aroma, style and quality. / AFRIKAANSE OPSOMMING: Tydens wynfermentasie dien talle druiwemosbestanddele as voedingstowwe vir wyngis (Saccharomyces
cerevisiae) wat hul groei bevorder en hul in staat stel om alkoholiese fermentasie suksesvol te voltooi.
Baie van hierdie voedingstowwe, veral stikstof, dien ook as voorlopers vir geurkomponente afkomstig
van gismetabolisme, soos hoër alkohole, esters en vlugtige vetsure. Die stikstofmetabolisme van gis speel
dus ‘n bepalende rol in wynaroma en -kwaliteit. Nie net is die stikstofbron, konsentrasie en
tydsberekening van stikstof toevoeging belangrik nie, maar verskeie omgewingsfaktore, asook die
genetiese samestelling van die gisras aangewend vir fermentasie, sal bydra tot die fermentasie uitkomste.
Die hoofdoel van hierdie werk was om die komplekse interaksies tussen ‘n aantal bydraende faktore te
ondersoek; naamlik die stikstofbron, tyd van stikstof toevoeging, gisras en fermentasiematriks. Breedweg
het hierdie studie die impak van sewe verskillende stikstofkombinasies, toegedien tot die druiwemos voor
of na die aanvang van fermentasie, op die suksesvolle verloop van fermentasie en die produksie van
aromakomponente deur nege kommersiële wyngisrasse bepaal. Fermentasies is in sintetiese druiwemos
uitgevoer, en ‘n deelversameling van die fermentasies in regte druiwesap te herhaal. Die
stikstofbehandelings is ontwerp in ooreenstemming met die algemeen vasgestelde voorkeurvolgorde van
S. cerevisiae vir individuele aminosure as stikstofbron onder fermentatiewe kondisies, en die potensiaal
van sekere aminosure om mee te doen in metaboliese paaie wat spesifieke aromaverbindings produseer.
Die resultate toon dat verskillende stikstofkombinasies tot onverwagte aroma-uitkomste kan lei wat sterk
afhanklik is van die genetiese agtergrond van individuele gisrasse en die tyd van stikstof byvoeging.
Sekere stikstofbehandelings het konsekwent, vir veelvuldige gisrasse, tot beduidende toenames of
afnames in die konsentrasies van spesifieke aromakomponente gelei in vergelyking met die behandeling
wat ammonium as enigste stikstofbron bevat het. Hierdie verbindings is as stikstofbehandeling afhanklik
geklassifiseer. Ander aromaverbindings is soortgelyk vir alle stikstofbehandelings geproduseer en is
aangewys as stikstofbehandeling onafhanklik. Die teenwoordigheid van spesifieke aminosuurgroepe
(byvoorbeeld die vertakte-ketting en aromatiese aminosure) kon gekorreleer word met beduidende
veranderings in produksiepatrone van verwante (soos hoër alkohole) of onverwante (dietielsuksinaat)
aromakomponente relatief tot die ander stikstofbehandelings. Alles inaggenome kon ‘n aantal interessante
en nuwe hipoteses rakende die betrokke metabolise padweë van die data afgelei word.
Uiteindelik sal hierdie aanvaklike bepaling van interaktiewe effekte tydens fermentasie bydra tot
praktiese riglyne vir wynmakers, wat hulle in staat sal stel om druiwesapbestanddele (soos nutriënte) te
strook met die intrinsieke aromaproduksie kapasiteite van spesifieke gisrasse, en sodoende wynaroma,
styl en kwaliteit te moduleer. / Oenobrands and THRIP for funding this project
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Factors influencing the style of brandyBougas, Nina Valleska 04 1900 (has links)
Thesis (PhD(Agric))-- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Brandy producers in South Africa can produce three categories of brandy, and within those categories, varies styles in order to cater for diverse consumer needs. Thus they have divergent opinions as to what comprises a good base wine and distillate for their individual end-product style in mind. Due to the fact that brandy is the largest locally produced spirit in South Africa, it is crucial to investigate the factors that influence the production of brandy as better understanding and control of these processes leads to the production of a brandy that is more consistent in quality and in style.
The factors known to influence the quality of brandy are the grape cultivar, vinification techniques, distillation and the oak maturation process; however limited research has been done on the factors contributing to the style of brandies. Understanding and identifying the factors that contribute to the style of brandy, will allow for better control and manipulation of the process to ultimately produce a spirit product with a desired style classification. In order to do so, one must distinguish as to what differentiates (chemical and sensory analyses) the two most divergent styles of brandy (in this study referred to as class one and class five three-year barrel matured brandy).
Over 104 three-year old barrel matured brandy samples were collected and analysed using GC-FID and HPLC analysis over a three year period. Of these samples, only 7 were classified as a class one three-year barrel matured brandy and 23 were found to be classified as class five three-year barrel matured brandy. The results obtained showed that the class one samples were found to contain a higher concentration of total higher alcohols, higher ratio of higher alcohols vs. esters, higher alcohols vs. acids and aldehydes vs. esters, but a lower level of total esters and acids. The class five samples contained a higher concentration of total esters, furans, lactones and acids, but a lower level of total higher alcohols and ratio of higher alcohols vs. esters.
The factors investigated that possibly influence the style of brandy were: the base wine prior to distillation, yeast strain, fermentation temperature, condenser water temperature and barrel age. Results of the base wine analysed prior to distillation show that those samples that scored a sensory score of one could produce a class one three-year barrel matured brandy, and base wines that scored a sensory score of five would yield a class five three-year barrel matured brandy. Alchemy 1 yeast was found to produce elevated levels of total esters and could by default result in a class five three-year barrel matured brandy. Similarly if the wine was fermented at 24⁰C it would result in the increased production of higher alcohols and total acids and in-turn could yield a class one three-year barrel matured brandy.
The results obtained show that the different condenser water temperatures do not necessarily influence the concentration of esters and higher alcohols. However, if a lower condenser water temperature (8⁰C) was employed, it could yield a class one barrel matured brandy sample. These distillates are associated with a higher concentration of total higher alcohols and even though they may be positively associated with higher levels of esters, the esters could be removed during the head fraction in the distillation process. The results also show that during the maturation process that the use of 18 year old barrels for the maturation of three-year barrel matured brandy samples could possibly produce a class one three-year barrel matured brandy and the use of new barrels could yield a class five three-year barrel matured brandy sample.
It is recommended that analysing the base wine prior to distillation using GC-FID to identify the chemical composition is the most important step in determining the outcome of the style of brandy. / AFRIKAANSE OPSOMMING: Brandewyn produsente in Suid-Afrika kan drie kategorieë brandewyn produseer, en binne hierdie kategorieë sekere style om voorsiening te maak vir die diverse behoeftes van die mark, en dus het hulle uiteenlopende menings oor wat 'n goeie basis wyn en distillaat behels vir hul individuele eindproduk se spesifieke styl. As gevolg van die feit dat brandewyn die belangrikste spiritus produk is wat deur die Suid-Afrikaanse bevolking verbruik word, is dit noodsaaklik dat dié faktore wat die produksie van brandewyn beïenvloed ondersoek word om 'n beter begrip van, en beheer oor hierdie prosesse verkry kan. Dit sal lei tot die produksie van 'n brandewyn van konstante in qualitiet en in style.
Die faktore wat bekend is om die gehalte van brandewyn te beïnvloed, is die druifkultivar, wynbereidingstegnieke, distillasie en die hout verouderings proses, maar daar is beperkte navorsing oor die faktore wat bydra tot die styl van n brandewyn. Om die faktore wat bydra tot die spesifieke styl van n brandewyn te identifiseer en te verstaan, kan dit lei tot 'n beter beheer en manipulasie van die prosess om uiteindelik n brandewyn met 'n gewenste styl te produseer. Ten einde dit te kan doen, moet 'n mens kan bepaal wat die twee uiterste style van brandewyn (wat in die studie sal bekend wees as klas een en klas vyf drie-jaar vat veroude brandewyn) van mekaar onderskei (chemiese en sensoriese analise).
Meer as 104 drie-jaar vat verouderde brandewyn monsters is ingesamel en ontleed met behulp van GC-FID en HPLC analyliese oor 'n tydperk van drie jaar. Van die 104 monsters, is slegs 7 as 'n klas een drie-jaar vat verourde brandewyn geklassifiseer en 23 as klas vyf drie-jaar vat verourde brandewyn geklassifiseer. Die resultate het getoon dat die klas een monsters 'n hoër konsentrasie van die totale hoër alkohole, 'n hoër verhouding van hoër alkohole teenoor esters het, hoër alkohole teenoor sure en aldehiede teenoor esters, maar 'n laer vlak van totale esters en sure. Die klas vyf monsters het 'n hoër konsentrasie van die totale esters, furanen, laktone en sure, maar 'n laer vlak van totale hoer alkohol en verhouding van hoër alkohole teenoor esters.
Die faktore wat ondersoek was wat moontlike ‘n invloed op die styl van brandewyn kon hê, was die basis wyn voor distillasie, die gisras, die fermentasie temperatuur, die kondensor water temperatuur en die vat ouderdom. Die ontledings van die basis wyn voor distillasie het gewys dat die monsters wat 'n sensorise telling van een behaal het, moontlik kan lei tot 'n klas een drie-jaar vat verouderde brandewyn, en basis wyne wat 'n sensorise telling van vyf gekry het weer ‘n klas vyf drie-jaar vat verouderde brandewyn sou oplewer. Alchemie 1 gis ras het ‘n verhoogde vlak van totale esters geproduseer wat tot 'n klas vyf drie-jaar vat verouder brandewyn gelei het As die basis wyn gefermenteer is teen 24⁰C sal dit lei tot die verhoogde produksie van hoër alkohole en totale sure wat 'n klas een drie-jaar vat verouderde brandewyn kan oplewer.
Die resultate verkry, toon dat die verskillende kondensor water temperature nie noodwendig die konsentrasie van esters en hoër alkohole beïnvloed het nie, maar dit wil voorkom dat indien 'n laer kondensor water temperatuur (8⁰C) gebruik is, kan dit 'n klas een vat verouderde brandewyn oplewer. Dit hou verband met 'n hoër konsentrasie van die totale hoër alkohole en selfs al word die distillate positief geassosieer met hoër vlakke van esters, kan die esters verwyder word tydens die verwydering van die voorloop in die distillasie proses.
Die resultate toon ook dat die gebruik van 18 jaar oue vate vir die veroudering van brandewyn moontlik 'n klas een drie-jaar vat verouderde brandewyn kan oplewer en die gebruik van nuwe vate kan 'n klas vyf drie-jaar vat verouderde brandewyn lewer.
Dit word egter aanbeveel dat die basis wyn voor distillasie met GC-FID chemies ontleed word om die samestelling van die wyn te identifiseer Die resultate bly die beste aanduiding van die styl van die brandewyn.
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Die toepassing van die tegniek van bedryfsvergelyking op kooperatiewe wynkelders in Suid-AfrikaBotha, Philip R. (Philip Rudolph) 03 1900 (has links)
Proefskrif (MScAgric)--Stellenbosch University, 1972. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming
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n Produksiekoste-ontleding van die private wynkelders in Suid-AfrikaVan Dyk, L. A. (Lodewyk August) 12 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 1969. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming
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Kinetic modelling of wine fermentations : why does yeast prefer glucose to fructoseMocke, Leanie 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In the present-day competitive global market, wine industries are constantly
aiming to improve the wine-making process,including the role of yeast. The
most commonly used wine yeast is Saccharomyces cerevisiae, which is able to
produce high quality wines, but problem fermentations do sometimes arise.
The occurrence of stuck and sluggish fermentations pose a serious problem
leading to loss of productivity and quality. Although the precise mechanism
leading to stuck fermentations is unknown, they are often correlated with
high fructose to glucose ratios in the wine-must. S. cerevisiae is a glucophylic
yeast, indicating its preference for consuming glucose over fructose. Both these
hexose sugars are present in unfermented wine must, mostly in equal concentrations.
As fermentation progresses, glucose is consumed at a faster rate than
fructose, leading to an increase in the fructose to glucose ratio. Yeast are left
with the undesirable fructose at the later stages of fermentation, when the
environmental stresses on the yeast can lead to stuck or sluggish fermentation.
This residual fructose can lead to undesirable sweetness, as fructose is
about twice as sweet as glucose. Even with the extensive research into yeast
metabolism, there is as yet no definitive explanation as to why yeasts ferment
glucose faster than fructose.
This study aimed to investigate the mechanism responsible for the faster consumption
of glucose over fructose of a commercially used wine yeast strain
S. cerevisiae VIN 13. The first two steps of sugar metabolism, uptake and
phosphorylation, were investigated as the possible sites of discrepancy in fermentation
rates. Enzyme rates and affinities for both glucose and fructose as substrates for the relevant enzymes were experimentally determined. These
kinetic parameter values were used to improve an existing model of yeast glycolytic
pathway to model wine fermentations. The feasibility of constructing
and validating a kinetic model of wine fermentations were investigated, by
comparing model predicted fluxes with experimentally determined fluxes.
Another aspect of this study was an investigation into the effect of hexose
sugar type on fermentation profiles. Wine fermentations were done with only
one hexose sugar as carbon source to determine if it has an effect on the flux
through metabolism.
This work succeeded in the construction of a kinetic model that distinguished
between glucose and fructose as carbon source. The glucose was consumed
faster than fructose, with control lying in the hexose transport step. It was
also established that fermentation prfiles of fermentations with only one sugar
was the same for both one sugar type fermentations. Fermentation with either
glucose or fructose as the sole carbohydrate source had the same specfic
production and consumption rates as normal fermentations with both sugars.
Construction of detailed kinetic models can aid in the metabolic and cellular
engineering of novel yeast strains. By identifying the importance of hexose
transport, and thus the glucophilic character of the yeast, in flux control, yeast
transporters can be targeted for strain improvement. This may in turn lead to
more effective fermentation practices for controlling problem fermentations, or
to the development of novel strains that utilizes fructose in the same manner as
glucose, and in so doing lower the risk of stuck or sluggish wine fermentation. / AFRIKAANSE OPSOMMING: In die hedendaagse kompeterende wynmark is wynmakers aanhoudend besig
om die wynmaak proses te verbeter en dit sluit die verbetering van wyngis
in. Die mees algemeenste gebruikte wyngis is Saccharomyces cerevisiae, omdat
dit wyn van gehalte produseer, maar probleem fermentasies kom wel voor.
Die verskynsel van vasval of stadige fermentasies kan lei tot die verlies van
produksie en kwaliteit. Die oorsaak van probleem fermentasies is gewoontlik
veelvoudig, maar die verhouding van glukose tot fruktose in die wyn-mos kan
ongunstig raak om fermentasies te onderhou. S. cerevisiae is 'n glukofiliese
gis, wat sy voorkeur om glukose bo fruktose te gebruik beskryf. Albei hierdie
heksose suikers is teenwoordig in ongefermenteerde wyn-mos, meestal in gelyke
hoeveelhede. Soos fermentasies vorder word glukose vinniger verbruik as
fruktose wat lei tot 'n toename in die fruktose tot glukose verhouding. Die gis
moet dus die fruktose in die later stadium van fermentasie gebruik wanneer
die omgewings druk op die gis kan lei tot probleem fermentasies. Die oorblywende
fruktose kan lei tot ongewenste soetheid aangesien fruktose twee keer
soeter is as glukose. Selfs met die ekstensiewe navorsing met betrekking tot
gis metabolisme is daar nog nie 'n verduideliking hoekom gis glukose vinniger
as fruktose gebruik nie.
Hierdie studie het beoog om die meganisme wat lei tot die vinniger verbruik
van glukose oor fruktose te ondersoek vir 'n kommersieël gebruikte gis S. cerevisiae VIN 13. Die eerste twee stappe van suiker metabolisme, suiker opname
en fosforilasie, was ondersoek as die moontlike punt van die verskil in fermentasie
tempo. Ensiem snelhede en affiniteite vir beide glukose en fruktose as substrate vir die ensieme van belang was eksperimenteel bepaal. Hierdie
waardes is gebruik om 'n bestaande model van gis glikolise aan te pas vir wyn
fermentasies. Die uitvoerbaarheid van saamstel en valideer van 'n kinetiese
model van wyn fermentasies was ondersoek, deur model voorspelde fluksie
waardes met eksperimentele fluksie waardes te vergelyk.
'n Ander aspek van die studie was die ondersoek van die effek van heksose
suiker tipe op fermentasie profiel. Wyn fermentasies is gedoen met slegs een
heksose suiker as koolstof bron om te bepaal of dit 'n invloed het op die fluksie
deur metabolisme.
Hierdie werk het daarin geslaag om 'n kinetiese model saamtestel wat onderskei
tussen glukose en fruktose as koolstof bron. Die glukose is vinniger verbruik as
fruktose, met beheer gesetel in die heksose opname stap. Dit was ook vasgestel
dat fermentasie profiele van fermentasies met slegs een suiker nie verskil het
vir fermentasies met slegs fruktose of glukose. Fermentasies met slegs een
suiker het dieselfde spesifieke produksie en konsumpsie tempo gehad as die
normale fermentasie met albei suikers. Die konstruksie van 'n gedetailleerde
kinetiese model kan gebruik word in die metaboliese en sellulêre ontwikkeling
van nuwe gisstamme. Deur die ontdekking van die belangrikheid van heksose
opname in fluksie beheer, wat lei tot die glukofiliese karakter van gis, kan gis
opname geteiken word vir gis ontwikkeling. Dit mag om die beurt lei tot meer
effektiewe fermentasie praktyk in die beheer van probleem fermentasies, of die
ontwikkeling van nuwe stamme wat fruktose in dieselfde manier as glukose
benut, en sodoende die risiko van vasval of stadige wyn fermentasies verlaag. / National Research Foundation / Post-graduate Merit Bursary
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n Studie van die mikro-organimes geassosieerd met die blomme en rypwordende korrels van 'n aantal druiwevarieteiteDu Plessis, L. de W. (Ludwig de Wet) 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 1959. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming
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Development of a novel LC-MS/MS method for the detection of adulteration of South African sauvignon blanc wines with 3-alkyl-2-methoxypyrazinesAlberts, P. 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2008. / A method for the detection of adulteration of South African Sauvignon blanc
wines, by enrichment with foreign sources of 3-alkyl-2-methoxypyrazenes, is
described. The levels of three 3-alkyl-2-methoxypyrazenes (3-isobutyl-, 3-
isopropyl- and 3-sec-butyl-2-methoxypyrazine) in South African Sauvignon blanc
wines were measured with liquid chromatography-mass spectrometry. Sample
preparation involved clean-up and pre-concentration by distillation followed by
solvent extraction of the distillate with dichloromethane. Extracts were acidified
and concentrated by evaporation and finally reconstituted to a fixed volume to
affect quantitative pre-concentration of the samples. Sample extracts were
separated with reversed phase liquid chromatography utilizing a phenyl-hexyl
separation column. Residues were measured with liquid chromatography-mass
spectrometry utilizing a tandem quadrupole mass spectrometric detector
operated in multiple reaction monitoring mode for optimal trace level quantitation.
Atmospheric pressure chemical ionization was utilized as electrospray ionization
was found to suffer from quenching effects attributed to the sample matrix.
Qualitative information was obtained from the relevant molecular ions as well as
two secondary ion transitions (and one ion ratio) in each case. Recoveries
obtained by the extraction procedure were better than 90% with coefficient of
variance of better than 10% at concentrations from 1 to 100 ng/L. The limit of
detection of the method was 0.03 ng/L and the limit of quantification 0.10 ng/L for
the three analytes measured. The described LC-MS method is more sensitive for
the determination of 3-alkyl-2-methoxypyrazines in wine than GC methods
reported for the same purpose.
From the experimental data, a set of parameters were established to discriminate
adulterated South African Sauvignon blanc wines. It was demonstrated that the
3-isobutyl-2-methoxypyrazine concentration, despite showing considerable
variance, was confined to a relatively narrow range spanning approximately two
orders of magnitude (0.20 to 22 ng/L). A clear indication of possible maximum values for this compound in South African Sauvignon blanc wines was obtained
from the analysis of a large number of samples (577), spanning most relevant
wine producing regions and representing vintages 2003 to 2006. It was also
demonstrated that South African Sauvignon blanc wines contain the major 3-
alkyl-2-methoxypyrazenes in reasonably distinct relative amounts and that the
said ratios of abundance may be used to elucidate authenticity. The expected
effect of adulteration with green pepper extracts or some synthetic preparations
on the 3-isobutyl-2-methoxypyrazine concentration as well as the relative
abundances were also determined by characterizing the corresponding profiles in
green peppers and some synthetic flavor preparations. Two adulterated samples
in the dataset were identified by both outlined criteria. A limited number of wines
of other cultivars were also analyzed. The results represent the most complete
and accurate data on the 3-alkyl-2-methoxypyrazine content of South African
Sauvignon blanc wines to date.
A publication covering the work presented in this thesis is currently in
preparation.
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Acolein in wine : bacterial origin and analytical detectionBauer, Rolene 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT:
Wine quality is compromised by the presence of 3-hydroxypropionaldehyde (3-HPA)
due to spontaneous conversion into acrolein under wine making conditions. Acrolein
is highly toxic and is presence has been correlated with the development of
bitterness in wine. Lactic acid bacterial strains isolated from South African red wine,
Lactobacillus pentosus and Lactobacillus brevis, are implicated in accumulating 3-
HPA during anaerobic glycerol fermentation. The environmental conditions leading
to its accumulation are elucidated. In aqueous solution 3-HPA undergoes reversible
dimerization and hydration, resulting in an equilibrium state between different
derivatives. Interconversion between 3-HPA derivatives and acrolein is a complex
and highly dynamic process driven by hydration and dehydration reactions. Acrolein
is furthermore highly reactive and its steady-state concentration in complex systems
very low. As a result analytical detection and quantification in solution is problematic.
This study highlights the roles played by natural chemical derivatives and shows that
the acrolein dimer can be used as a marker for indicating the presence of acrolein in
wines. Solid-phase microextraction (SPME) coupled to gas chromatograph mass
spectrometry (GC-MS) was validated as a technique for direct detection of the
acrolein dimer in wine. The potential of a recently introduced sorptive extractive
technique with a sample enrichment probe (SEP) was also investigated. The SPME
technique simplifies the detection process and allows for rapid sampling of the
acrolein marker, while SEP is more sensitive. / AFRIKAANSE OPSOMMING:
Die teenwoodigheid van 3-hidroksiepropioonaldehied (3-HPA) in wyn het ‘n
negatiewe invloed op kwaliteit as gevolg van die moontlike omskakeling na akroleien
tydens die wynmaak prosses. Akroleien is hoog toksies en is moontlik betrokke by
die ontwikkeling van ‘n bitter komponent in wyn. Hierdie studie wys dat stamme van
die melksuurbakteriëe Lactobacillus pentosus en Lactobacillus brevis, geisoleer uit
Suid-Afrikaanse wyn, 3-HPA tydens anaerobiese alkoholiese fermentasie kan opbou.
Kondisies wat ontwikkeling beinvloed is bestudeer. 3-HPA ondergaan omkeerbare
dimerisasie en hidrasie in oplossing en het ‘n ewewig tussen veskillende derivate tot
gevolg. Omkakeling tussen 3-HPA derivate en akroleien is ‘n komplekse en hoogs
dinamiese prosses wat gedryf word deur hidrasie en dehidrasie reaksies. Akroleien
is verder hoogs reaktief en die ewewigskonsentrasie van hierdie aldehied in
komplekse omgewings is laag. Analitiese waarneming en kwantifisering is gevolglik
problematies. Hierdie studie lig die rol wat natuurlike chemise derivate speel duidelik
uit en wys dat die akroleien dimeer as ‘n merker gebruik kan word om die
teenwoodigeid van akoleien in wyn te staaf. Soliede-fase mikro-ekstraksie (SPME)
gekoppel aan gas chromatografie massa spektroskopie (GC-MS) is gevalideer as ‘n
tegniek vir die direkte waarneming van die akroleien dimeer in wyn. Die potensiaal
van ‘n nuwe ekstraksie tegniek, gebasseer op ‘n peiler wat vir die monster verreik
(SEP), was ook ondersoek. Die SPME tegniek is vinnig en vergemaklik analiese,
terwyl SEP meer sensitief is.
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