Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The alcoholic beverage industry needs objective analysis of grape juice and liqueur quality. Fourier transform infrared (FT-IR) spectroscopy with multivariate data analysis techniques is widely used in wine laboratories across South Africa for accurate, fast and high sample throughput analyses. In this study the potential of FT-IR spectroscopy is evaluated for the quantification of ammonia in freshly pressed grape juice. FT-IR spectroscopy is evaluated, using two different spectrometers, in respectively attenuated total reflection (ATR) - and transmission scanning modes for the quantification of alcohol, pH and invert sugar in spirit-based liqueurs. The ultimate aim was to implement the PLS regression algorithms developed at an industrial cellar and replace the complex and lengthy reference methods used at the time of this study. Principle component analysis (PCA) was performed prior to the calibration step to identify groupings and patterns within the spectra. The PLS calibration models were developed from samples collected at the cellar and using partial least square (PLS) regression. The models were evaluated using the performance criteria coefficient of determination (R2) and root mean squared error of cross validation (RMSECV) at calibration stage, and root mean square error of prediction (RMSEP) and residual predictive deviation ratio (RPD) at validation stage. The average RMSEP (1.88 mg/L) of the ammonia PLS calibration model was in agreement with the standard error of laboratory (SEL = 1.54 mg/L). The R2 (92.05) and average RPD (3.3) proposed a model with excellent precision for screening purposes that was ready to be transferred for use by the laboratory. The r2 values for the alcohol, pH and invert sugar PLS calibration models obtained in ATR and transmission, indicated good to excellent precision (80<r2<100). The alcohol PLS calibration model obtained in transmission was suitable for quality- and process control purposes (RPD = 21.2), while the invert sugar PLS calibration model for quality control purposes (5<RPD<6.4). The pH and invert sugar calibration models obtained in ATR were suitable for screening purposes with RPD = 3.6 and RPD = 4.8, respectively. These PLS regression algorithms were implemented at the cellar. The pH PLS calibration model obtained in transmission was suitable for rough screening of samples (RPD = 2.7) and future development was neccesary to increase the predictability of the model. The results obtained in this study made a significant contribution towards validation of FT-MIR as a powerful tool for rapid quantification of quality indicating parameters in wine and spirit-based liqueurs. The contribution is particularly valuable in the context of ongoing research to improve the quality of products at the cellar to meet consumer demands. The knowledge gained on quantification of quality indication parameters of spirit-based liqueurs is novel and this is one of the first reports on implementation of mid-infrared (MIR) spectroscopy for the quality control of South African spirit-based liqueurs. / AFRIKAANSE OPSOMMING: Die wynindustrie benodig objektiewe analises van druiwesap- en likeurgehalte. Fourier-transformasie- infrarooi (FT-IR) spektroskopie met multiveranderlike statistiese metodes word gebruik in wynlaboratoriums regoor Suid-Afrika vir akkurate, vinnige en hoë monsterdeurset ontledings. In hierdie studie is die potensiaal van FT-IR spektroskopie geëvalueer vir die kwantifisering van ammoniak in die sap van vars geparste wyndruiwe. Twee verskillende FT-IR spektroskopie instrumente, in onderskeidelik (verswakte totale refleksie, ATR) - en transmissie skandering is gebruik vir die kwantifisering van alkohol, pH en invertsuiker in spiritus-gebaseerde likeurs. Die uiteindelike doel was om die parsiële kleinste kwadraat (PKK)- regressie algoritmes wat ontwikkel is, by 'n industriële kelder te implementeer en die komplekse en tydrowende verwysingmetodes wat tydens die studie in die kelder gebruik is te vervang. Verskeie multiveranderlike hoofkomponentanalise (MVK) is uitgevoer voor die kalibrasie stap, met die doel om groeperings en patrone in die spektra te identifiseer. Die PKK kalibrasiemodelle is ontwikkel van monsters wat by die kelder versamel is en die spektra is gebruik in die PKK regressies. Tydens die kalibrasiefase is die modelle geëvalueer met behulp van die bepalingskoëffisiënt (R2) en gemiddelde kalibrasieprediksiefout en tydens die validasiefase, met behulp van die standaardvoorspellingsfout (SVF) en relatiewe voorspellingsafwyking (RVA). Die gemiddelde SVF (1.88 mg/L) van die ammoniak kalibrasiemodel was in ooreenstemming met die standaard fout van die laboratorium (SEL = 1.54 mg/L). Die R2 (92.05) en die gemiddelde RVA (3.3) dui op ‘n model met uitstekende presiesheid wat gereed is vir oordra en gebruik deur die industrie. Die R2 waardes vir die alkohol-, pH- en invertsuiker –kalibrasie-modelle wat met ATR en transmissie vir die likeurmonsters ontwikkel is, dui op goeie tot uitstekende presiesheid (80<R2<100). Die alkoholkalibrasiemodel wat ontwikkel is in transmissie, is geskik vir kwaliteits- en prosesbeheerdoelwitte (RVA = 21.2), terwyl die invertsuiker kalibrasiemodel geskik is vir kwaliteitsbeheer doelwitte (5<RVA<6.4). Die pH en invertsuiker kalibrasiemodelle in ATR is geskik vir vinnige evalueringsdoelwitte, met RVA = 3.6 en RVA = 4.8 waardes, onderskeidelik. Hierdie algoritmes is ook in die kelder geimplementeer. Die pH kalibrasiemodel in transmissie was geskik vir vinnige evalueringsdoelwitte (RVA = 2.7) en toekomstige ontwikkeling is nodig om die voorspellingsakkuraatheidvan die model te verbeter. Die resultate van hierdie studie het ‘n betekenisvolle bydrae gelewer tot bevestiging van infrarooi spektroskopie as 'n kragtige tegnologie vir die vinnige kwantifisering van gehalteparameters in druiwesap en spiritus-gebaseerde likeurs. Die bydrae is veral waardevol in die konteks van voortgesette navorsing om die kwaliteit van produkte by die kelder te verbeter en aan verbruikerseise te voldoen. Die studie vir die kwantifisering van gehalteparameters in spiritus-gebaseerde likeurs is eerste in sy soort en een van die gerapporteerde verslae vir die implementering van infrarooi spektroskopie vir gehaltebeheer van Suid-Afrikaanse spiritus-gebaseerde likeurs.