Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The removal of grape berries from the stems is an important step in the wine making process. Various problems are experienced using the destemming machines currently available, where the berries are mechanically removed and separated from the stems by a rotating beater shaft and drum. Not all berries are removed from the stems and broken stems can end up with the removed berries which can result in unwanted characters and flavours in the wine. The development of these machines is currently limited to experimental tests. In this study, the destemming process was investigated experimentally. The ability of the Discrete Element Method (DEM) to simulate this process was also investigated. A range of experiments was designed to obtain the material properties of the grapes. These experiments included the measurement of the stem stiffness and break strength, the berry stiffness, and the force needed to remove a berry from the stem. Experiments were conducted to gain further insight into the destemming process. Firstly, a simplified destemming machine with only a beater shaft and a single grape bunch was built. The influence of the bunch size and the speed of the beater shaft on the number of berries removed from the stems were investigated. Secondly, field tests on a commercial destemming machine were conducted and the performance of the machine was measured. A DEM model of both the simplified and the commercial destemming machine were built. Commercial DEM software was used with linear contact and bond models. The stems were built from spherical particles bonded together and a single spherical particle was used to represent each berry. The measured stiffnesses and break strengths were used to set the particle and bond properties. Modelling the simplified destemming machine, it was found that the DEM model could accurately predict the effect of the bunch size and the speed of the beater shaft on the number of berries removed from the stems. The model of the commercial destemming machine could accurately predict the machine’s performance in terms of the number of berries removed as well as the number of broken stems. / AFRIKAANSE OPSOMMING: Die verwydering van druiwekorrels vanaf die stingels is ʼn belangrike stap tydens die wynmaak proses. Verskeie probleme word ondervind met huidige beskikbare ontstingelaars, waar die korrels meganies verwyder en skei word vanaf die stingels deur middel van ʼn roterende klop-as en drom. Nie alle korrels word vanaf die stingels verwyder nie en gebreekte stingels kan saam met die verwyderde korrels beland, wat ongewensde karakters en geure in die wyn kan veroorsaak. Die ontwikkeling van ontstingelaars is tans beperk tot eksperimentele toetse. In hierdie studie is die ontstingel proses eksperimenteel ondersoek Die vermoë van die Diskrete Element Metode (DEM) om hierdie proses te simuleer is ook ondersoek. ʼn Reeks eksperimente is ontwikkel om die materiaal eienskappe van die druiwe te bepaal. Hierdie eksperimente sluit in die meet van die styfheid en breeksterkte van die stingel, die korrel styfheid, en die krag benodig om ʼn korrel vanaf die stingel te verwyder. Eksperimente is gedoen om verdere insig oor die ontstingel proses te bekom. Eerstens is ʼn vereenvoudigde ontstingelaar gebou, met slegs ʼn klop-as en een tros. Die invloed van die trosgrootte en die klop-as spoed op die aantal korrels wat verwyder is, is ondersoek. Tweedens is ʼn toets in die veld gedoen met ʼn kommersiële ontstingelaar om die werkverrigting van die masjien te bepaal. ʼn DEM model van beide die vereenvoudigde en kommersiële ontstingelaar is gebou. Kommersiële DEM sagteware is gebruik met lineêre kontak- en bindingsmodelle. Die stingels is gebou deur sferiese partikels aan mekaar te bind en ʼn enkele sferiese partikel is gebruik om ʼn druiwe korrel voor te stel. Die gemete styfhede en breeksterktes is gebruik om die partikel- en bindingseienskappe te spesifiseer. Die modellering van die vereenvoudigde ontstingelaar het getoon dat die DEM model akkuraat kan voorspel wat die invloed is van die trosgrootte en die klop-as spoed op die aantal korrels wat verwyder is. Die model van die kommersiële ontstingelaar kon die werkverrigting van die masjien akkuraat voorspel in terme van die aantal korrels wat verwyder is asook die aantal gebreekte stingels.

Thesis (MScAgric)--Stellenbosch University, 1992. / One microfiche copy / ENGLISH ABSTRACT: The possibility of harvesting grapes at an earlier stage of maturity, based on differences in glucose and fructose concentration which influence the sweetness of grapes, was investigated. Although differences between cultivars were found the extent was not such that a specific cultivar could be selected in order to harvest at a lower sugar concentration, but with the same sweetness. Certain characteristics of table and wine grape cultivars with respect to anatomical composition and skin penetration resistance (SPR) were also investigated in order to ascertain the extent to which grapes would resist external damage, and to what extent turgor and skin thickness contributed to SPR. Daily variances in SPR confirm that not only skin strength, but also the turgor of the grape berry contributed to SPR. Skin penetration resistance seems to be a good criterion of the extent to which cultivars would resist external damage, because it is based on the toughness of the skin and the turgor of the berry. / AFRIKAANSE OPSOMMING: Die moontlikheid van vroeer oes op grond van verskille in die glukose- en fruktosekonsentrasie wat 'n invloed op die soetheid van druiwe mag he, is ondersoek. Daar is gevind dat die verskille wat tussen cultivars voorkom nie van so 'n grootte-orde is dat 'n spesifieke cultivar geselekteer kan word ten einde by 'n laer totale suiker, maar by dieselfde soetheidsgraad, te kan oes nie. Verder is sekere eienskappe van tafel- en wyndruifcultivars t.o.v. anatomiese samestelling en doppenetrasieweerstand (DP\V) ondersoek om die moontlike weerstand teen eksterne beserings en die mate waartoe turgor en dopdikte 'n invloed daarop mag uitoefen, _vas te stel. Daaglikse variasie in DPW het bevestig dat die DPW nie alleen afhanklik is van dopsterkte nie, maar ook van die turgor van die korrel. Doppenetrasieweerstand blyk 'n goeie maatstaf te wees vir die mate waartoe cultivars weerstand hied teen sekere eksterne beserings omdat dit gebaseer is op dopsterkte en turgor van die korrel.

Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2007. / A common phenomenon in most South African vineyards, especially in the Western Cape region, is that of within vineyard variation. This variation phenomenon is caused by an array of controllable and non-controllable factors that interact with each other to affect vine vigour. Controllable factors can be managed by the grape grower, while the non-controllable factors have to be managed in the planning process in order not to negatively affect productivity or product quality. The main goal of any grape grower is to optimise vine performance in an attempt to achieve the best possible yield while at the same time allowing vines to optimally ripen grapes towards optimal wine quality. A grape grower has to use every possible means and technique available to him in order to manage his vineyards in such a manner as to achieve this goal. In the past, it was difficult to visualize the extent and distribution of vigour variation in vineyards, but with modern technological improvements in the field of remote sensing, grape growers are able to identify and specify different vigour levels within a vineyard. When remote sensing is applied in a vineyard, the grape grower can identify certain areas that may need more specific attention than others. Consequently, managerial decisions based on detailed information can be made in an attempt to improve the general condition and performance of a vine. Not only can the acquired information be used to plan managerial actions throughout the season, but it can also be used to plan and devise harvest strategies. Some areas in a vineyard may be at a certain point in the ripening process and need to be harvested, while grapes from other areas still need to develop the wanted flavours. One managerial action applied at véraison by some grape growers, is that of crop thinning. Different vigour areas can now be subjected to various crop thinning actions in an attempt to determine the best crop load for a vigour level. With this in mind, two studies were launched to firstly investigate the interaction between vine vigour and harvest dates; and secondly to investigate the interaction between vine vigour and crop load and how their combined interaction might influence a vine’s characteristics, grape composition and wine quality. Vigour variation was firstly identified through multispectral aerial imagery, and then visually verified by visits to the experimental vineyards. The multispectral aerial image was then “orthorectified” in order to produce a classified multispectral image. The image was classified through different colour codes that were assigned to the different vigour levels to clearly distinguish between them. A series of vegetative and reproductive measurements were conducted to try and establish if any correlations could be obtained of the interaction between vine vigour, different harvest dates and crop loads. In order to verify differences in vine vigour, underlying causes were also determined through soil analyses of which chemical analysis, bulk density, porosity, as well as root penetration and distribution were determined. Vegetative measurements that were conducted for both studies indicated good correlations between the different vigour levels and the image classifications. The results also identified the effect that topping (mechanical or manual) had on the main and lateral leaf areas. Reproductive measurements throughout the season, in the form of berry sampling, showed changes in berry composition and accentuated the effects of the different treatments, which could also be confirmed through sensorial analysis of the wines. The results also emphasized the need to not only make use of one of two chemical parameters to identify grape ripeness, but to incorporate a number of parameters, such as sugar, pH and acid levels. From the varying grape chemical characteristics, a wine style can be identified that might carry the approval of the winemaker for the production of a specific type of wine. Soil studies of both vineyards also gave important evidence for the causes of vigour variation. The data collected will hopefully provide grape growers with information that will enable them to make educated decisions concerning grape production and how vigour, in conjunction with different harvest dates and crop loads, will enable them to produce fruit of good quality and, so doing, improve their financial position.

Thesis (MSc (Logistics))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Technological advances made over the past century have had a major impact on traditional wineries. Software solutions for management issues are widely available and give rise to the prospect of computerized decision support systems assisting in various aspects of managing a winery. The most popular applications seem to be concerned with supply chain management or harvest scheduling. Such projects are under way all over the globe and great success has been achieved to this e ect. However, prior to this study no such project has been considered in South Africa. The phrase active cellar scheduling problem refers to the assignment of grape batches to processors inside the cellar where bottlenecks often occur during the busy harvesting period. The phrase harvest scheduling problem, on the other hand, refers to selecting the best possible dates to harvest the respective vineyard blocks in order to preserve grape quality. A mixed integer programming model for the active cellar scheduling problem is derived in this thesis, but proves to be too time consuming to solve exactly via the branch-and-bound method. A meta-heuristic tabu search approach is therefore designed to solve the problem approximately instead. When applied to a small, ctitious cellar, it is found that the tabu search method often solves the problem optimally. The computer processing time associated with the tabu search approach also constitutes a signi cant (often thousand-fold) improvement over that of the branch-and-bound approach for realistically sized problem instances. A generic tabu search is also designed to solve the over-arching harvest scheduling problem for a general winery. This schedule is found by referring to the smaller tabu search of the active cellar scheduling in order to verify the impact that harvesting moves have on activities in the cellar. One harvesting schedule is considered a better schedule than another when it has a lower harvest evaluation score, determined by the placement of the vineyard blocks in the harvesting schedule. The harvest evaluation score takes into account the combination of vineyard blocks selected for harvesting on the same day (and their e ect on the active cellar) as well as the ripeness and quality of the grapes. Both tabu searches are nally included in a exible, computerized decision support system, called VinDSS. This system is found to produce good harvesting schedules when compared to an actual ve day schedule during the 2009 harvesting period at Wamakersvallei, a winery serving as case study for this thesis. / AFRIKAANSE OPSOMMING: Tegnologiese vooruitgang oor die afgelope eeu het 'n groot invloed op tradisionele wynkelders gehad. Sagteware-oplossings wat besluitsteun tot bestuursaangeleenthede bied, is algemeen beskikbaar en het gelei tot die rekenaarmatige implementering van besluitsteunstelsels vir wynkelders. Dit blyk dat die mees popul^ere besluitsteuntoepassings in die wynindustrie te make het met besluite rakende van voorsieningskettings en oes-skedulering. Sulke besluitsteunprojekte is w^ereldwyd onderweg en het alreeds groot sukses behaal. Daar is egter tot dusver geen so 'n projek in Suid-Afrika onderneem nie. Die frase aktiewe kelderskeduleringsprobleem verwys na die toekenning van druifvragte aan masjiene binne die kelder waar bottelnekke algemeen tydens die besige parstydperk voorkom. Die frase oes-skeduleringsprobleem, daarenteen, verwys na die seleksie van bes moontlike oesdatums vir elk van die wingerdblokke om sodoende druifkwaliteit te verseker. 'n Gemengde heeltallige programmeringsmodel is vir die aktiewe kelderskeduleringsprobleem ontwikkel, maar die rekenaaroplossingstyd van hierdie benadering blyk te lank te wees om die probleem eksak deur middel van 'n vertak-en-begrens metode op te los. 'n Meta-heuristiese tabu soektog is dus ontwikkel om die probleem benaderd op te los. Wanneer hierdie benadering op 'n klein, ktiewe kelder toegepas word, word optimale oplossings dikwels verkry. Verder toon die rekenaaroplossingstyd van die tabu soektog 'n groot (in sommige gevalle byna 'n duisendvoudige) verbetering op di e van die eksakte oplossingsmetode. 'n Generiese tabu soektog is ook ontwikkel om die oorkoepelende oes-skeduleringsprobleem vir 'n algemene wynkelder op te los. So 'n oes-skedule word gevind deur na die kleiner tabu soektog vir die aktiewe kelderskedulering te verwys om sodoende die e ekte van veranderinge in die oesskedule op die prosesse binne die aktiewe kelder na te speur. Een oes-skedule word beter as 'n ander skedule beskou wanneer dit met 'n beter oes-evalueringswaarde gepaard gaan, soos deur die plasing van die wingerdblokke in die skedule bepaal. Die oes-evalueringswaarde neem die moontlike kombinasies van wingerblokke wat op dieselfde dag geoes word, in ag (en ook die e ek wat dit op aktiwiteite in die kelder het), asook die rypheid en kwaliteit van die druiwe. Beide tabu soektogte word in 'n plooibare, rekenaar-ge mplementeerde besluitsteunstelsel, bekend as VinDSS, ingesluit. Daar word gevind dat hierdie stelsel goeie oes-skedules lewer wanneer dit vergelyk word met 'n werklike vyf-dag skedule tydens die 2009 parsseisoen van Wamakersvallei, die kelder wat as gevallestudie vir hierdie tesis gedien het.