Mathematical modelling of salt diffusion in dry-salted cheese : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Engineering at Massey University, Manawatu, New Zealand

Figures are re-used with permission.Control of salt uptake into cheese curds is vital to the production of safe, functional, and consistent cheese products. Development of mathematical models describing the mechanisms affecting salt uptake, namely the Fickian diffusion of salt into curds and osmotic pressure differential induced whey expulsion, are necessary to control curd properties, optimize salt uptake, and reduce final product inconsistency in commercial cheesemaking plants. Novel image analysis techniques were developed to assess whey expulsion behaviour in individual model renneted skim milk gels under different brining conditions. Whey expulsion results were combined with salt uptake data to develop mechanistically-derived mathematical models of the simultaneous whey expulsion and salt uptake under brining conditions. Whey expulsion data was combined with gel meso-structural properties to estimate the pressure gradients driving the whey expulsion behaviour. Finally, the simultaneous salt uptake and whey expulsion models were used to model salt and whey transport in model renneted gels treated under different dry salting conditions and compared to samples collected from an industrial cheesemaking plant. This work developed new techniques to evaluate whey expulsion in individual curds, demonstrated the importance of accounting for whey expulsion in the evaluation of salt uptake and modelling, and applied mathematical models describing simultaneous salt uptake and whey expulsion to milk gels exposed to brining and dry salting conditions

The 9-MilCA method as a rapid, partly automated protocol for simultaneously recording milk coagulation, curd firming, syneresis, cheese yield, and curd nutrients recovery or whey loss

Abstract The aim of this study was to propose and test a new laboratory cheesemaking procedure [9-mL milk cheesemaking assessment (9-MilCA)], which records 15 traits related to milk coagulation, curd firming, syneresis, cheese yield, and curd nutrients recovery or whey loss. This procedure involves instruments found in many laboratories (i.e., heaters and lacto-dynamographs), with an easy modification of the sample rack for the insertion of 10-mL glass tubes. Four trials were carried out to test the 9-MilCA procedure. The first trial compared 8 coagulation and curd firming traits obtained using regular or modified sample racks to process milk samples from 60 cows belonging to 5 breeds and 3 farms (480 tests). The obtained patterns exhibited significant but irrelevant between-procedure differences, with better repeatability seen for 9-MilCA. The second trial tested the reproducibility and repeatability of the 7 cheesemaking traits obtained using the 9-MilCA procedure on individual samples from 60 cows tested in duplicate in 2 instruments (232 tests). The method yielded very repeatable outcomes for all 7 tested cheese yield and nutrient recovery traits (repeatability >98%), with the exception of the fresh cheese yield (84%), which was affected by the lower repeatability (67%) of the water retained in the curd. In the third trial (96 tests), we found that using centrifugation in place of curd cooking and draining (as adopted in several published studies) reduced the efficiency of whey separation, overestimated all traits, and worsened the repeatability. The fourth trial compared 9-MilCA with a more complex model cheese-manufacturing process that mimics industry practices, using 1,500-mL milk samples (72 cows, 216 tests). The average results obtained from 9-MilCA were similar to those obtained from the model cheeses, with between-method correlations ranging from 78 to 99%, except for the water retained in the curd (r=54%). Our results indicate that new 9-MilCA method is a powerful research tool that allows the rapid, inexpensive, and partly automated analysis processing 40 samples per day with 2 replicates each, using 1 lacto-dynamograph, 2 heaters, and 3 modified sample racks, and yields a complete picture of the cheesemaking process (e.g., milk gelation, curd firming, syneresis, and whey expulsion) as well as the cheese yield and the efficiency of energy or nutrients retention in the cheese or loss in the whey

A method for the inline measurement of milk gel firmness using an optical sensor

At present, selection of cutting time during cheesemaking is made based on subjective methods, which has effects on product homogeneity and has prevented complete automation of cheesemaking. In this work, a new method for inline monitoring of curd firmness is presented. The method consisted of developing a model that correlates the backscatter ratio of near infrared light during milk coagulation with the rheological storage modulus. The model was developed through a factorial design with 2 factors: protein concentration (3.4 and 5.1%) and coagulation temperature (30 and 40°C). Each treatment was replicated 3 times; the model was calibrated with the first replicate and validated using the remaining 2 replicates. The coagulation process was simultaneously monitored using an optical sensor and small-amplitude oscillatory rheology. The model was calibrated and successfully validated at the different protein concentrations and coagulation temperatures studied, predicting the evolution of storage modulus during milk coagulation with coefficient of determination values >0.998 and standard error of prediction values <3.4 Pa. The results demonstrated that the proposed method allows inline monitoring of curd firming in cheesemaking and cutting the curd at a proper firmness to each type of cheese

Breed of goat affects the prediction accuracy of milk coagulation properties using Fourier-transform infrared spectroscopy

The prediction of traditional goat milk coagulation properties (MCP) and curd firmness over time (CFt) parameters via Fourier-transform infrared (FTIR) spectroscopy can be of significant economic interest to the dairy industry and can contribute to the breeding objectives for the genetic improvement of dairy goat breeds. Therefore, the aims of this study were to (1) explore the variability of milk FTIR spectra from 4 goat breeds (Camosciata delle Alpi, Murciano-Granadina, Maltese, and Sarda), and to assess the possible discriminant power of milk FTIR spectra among breeds, (2) assess the viability to predict coagulation traits by using milk FTIR spectra, and (3) quantify the effect of the breed on the prediction accuracy of MCP and CFt parameters. In total, 611 individual goat milk samples were used. Analysis of variance of measured MCP and CFt parameters was carried out using a mixed model including the farm and pendulum as random factors, and breed, parity, and days in milk as fixed factors. Milk spectra for each goat were collected over the spectral range from wavenumber 5,011 to 925 × cm−1. Discriminant analysis of principal components was used to assess the ability of FTIR spectra to identify breed of origin. A Bayesian model was used to calibrate equations for each coagulation trait. The accuracy of the model and the prediction equation was assessed by cross-validation (CRV; 80% training and 20% testing set) and stratified CRV (SCV; 3 breeds in the training set, one breed in the testing set) procedures. Prediction accuracy was assessed by using coefficient of determination of validation (R2VAL), the root mean square error of validation (RMSEVAL), and the ratio performance deviation. Moreover, measured and FTIR predicted traits were compared in the SCV procedure by assessing their least squares means for the breed effect, Pearson correlations, and variance heteroscedasticity. Results showed the feasibility of using FTIR spectra and multivariate analyses to correctly assign milk samples to their breeds of origin. The R2VAL values obtained with the CRV procedure were moderate to high for the majority of coagulation traits, with RMSEVAL and ratio performance deviation values increasing as the coagulation process progresses from rennet addition. Prediction accuracy obtained with the SCV were strongly influenced by the breed, presenting general low values restricting a practical application. In addition, the low Pearson correlation coefficients of Sarda breed for all the traits analyzed, and the heteroscedastic variances of Camosciata delle Alpi, Murciano-Granadina, and Maltese breeds, further indicated that it is fundamental to consider the differences existing among breeds for the prediction of milk coagulation traits

Measurement of syneretic properties of rennet-induced curds and impact of factors such as concentration of milk: A review

peer-reviewedBackground The rate or extent of whey expulsion or syneresis from cheese curds during stirring in-vat determines curd moisture levels, which subsequently influences cheese moisture content. The outward migration of whey depends on curd contraction and on the structure of the pores permitting whey movement. Curd syneretic properties are one of the least understood areas of cheese science, particularly when milk of varying composition is used. Scope and approach This review provides an insight into the mechanisms of curd formation and curd syneresis, and factors influencing syneretic properties in unconcentrated and concentrated milk and appraises syneresis measurement methods in terms of their relative strengths and weaknesses. Key findings and conclusions Direct measurement of moisture content of curds is recommended as a simple and reliable method for measurement of syneresis of industrial relevance and, although inline measurement for curd moisture prediction has been a significant development in the last decade, its application to commercial production is still limited. A review of previous studies found that experimental conditions and methodologies used to measure syneresis vary widely, making it difficult to compare data between studies. Overall, interactions between process variables employed determines whether syneresis is accentuated or inhibited, and this can be exploited by cheese producers to attain target curd moisture contents by varying process parameters, particularly when milk is concentrated prior to cheese-making. Furthermore, further studies should be focused on endogenous syneresis and casein network rearrangement to clearly elucidate this mechanism and its influence on macrosyneresis under dynamic conditions

The impact of milk properties and process conditions on consistency of rennet-coagulated curd and syneresis of rennet curd grains

Although cheesemaking is an ancient art, modern cheese production relies on the implementation of innovative technology and tailor-made starter bacteria to remain competitive in the production of commodity-type cheeses such as soft and semi-hard cheese. Any intervention in the cheesemaking procedure, i.e. in milk composition, milk treatment and microbial fermentation, affects textural properties of curd at cutting and finally syneresis. The latter is the key step in cheesemaking since the degree of syneresis determines the moisture content of the raw cheese, by which ripening as well as rheological properties and sensory are affected. This work aimed to investigate the syneresis of rennet curd grains in order to generate a kinetic model for predicting syneresis. On the one hand, the experiments covered the implementation of EPS-(exopolysaccharide producing) cultures in the manufacture of soft cheese and likewise the investigation of the cheesemaking potential of Dahlem Cashmere goat?s milk. On the other hand, the interrelated effects of homogenization, microfiltration and pH on rheological properties of rennet-induced milk gels, on syneresis and finally on cheese composition, yield and functionality were to study. Three mathematical models were compared for their suitability describing syneresis and providing kinetic parameters. The kinetic parameters obtained by a linearised model gave best curve fittings to the experimental data with high coefficient of correlation (r² > 0.99). Furthermore, the model provides a parameter (RWRmax) that gives information about the endpoint of syneresis. From this value, interpretation about the curd structure and the interaction of milk composition and physical factors on syneresis is possible. Fermentation media inoculated with non-EPS-producing Streptococcus thermophilus and EPS-producing strains of Lactococcus lactis subsp. cremoris and Lactobacillus sakei were added in a concentration from 5 % to 10 % (w/w) to the milk prior to soft cheese manufacture. The cheesemaking experiments showed that the addition of fermentation media with EPS-cultures retarded syneresis, accelerated microbial fermentation and finally caused ripening problems. By means of model experiments regarding syneresis and influence of pH value, the manufacture of soft cheese was technologically adapted. The approach demonstrated that soft cheese manufacture was yet feasible and moisture content of the raw cheese was increased by the addition of fermentation media, inoculated with EPS-cultures. Analysis of variance revealed that syneresis was significantly affected by homogenization, MF and pH. It was shown that milk composition and MF markedly influenced the endpoint of syneresis, RWRmax. Curd grains made from skim milk had the highest RWRmax value. It is assumed, that differences in curd microstructure due to fat globule distribution and content affect syneresis since cutting was performed at equal curd firmness. The experiments demonstrate that homogenization and MF can be combined to reach curd firmness and syneresis which are in accordance with values in conventional cheesemaking. Combination of homogenization and MF was promising on cheese yield, and based on the results and experience gained in this study, a new and simplified process for semi-hard cheesemaking was invented. It was shown, that the adjusted cheese yield and component recovery increased due to the interaction of homogenization and MF. Hence, the combination of homogenization and MF in cheese manufacture is promising.Obwohl das Herstellen von Käse ein sehr altes Gewerbe ist, ist das Implementieren innovativer Technologien und maßgeschneiderter Starterbakterien notwendig, um in der modernen Herstellung von Weich- und Schnittkäse wettbewerbsfähig zu bleiben. Jeglicher Eingriff in den Käsungsprozess, d.h. in die Zusammensetzung und Behandlung der Milch, sowie in fermentative Vorgänge, beeinflusst die Textureigenschaften der Labgele und letzten Endes die Synärese. Letztere ist der wesentliche Prozessschritt bei der Käseherstellung, da der Synäresegrad den Serumgehalt im Rohkäse bestimmt, wodurch der Reifungsprozess sowie die rheologischen und sensorischen Eigenschaften beeinflusst werden. Die Arbeit hatte zum Ziel, die Synärese von Bruchwürfeln zu verfolgen, um ein kinetisches Modell zu generieren, anhand dessen die Synärese vorhersagbar wird. Einerseits waren die Experimente auf das Einbringen von EPS- (Exopolysaccharid-bildende) Kulturen in die Weichkäseherstellung sowie auf die Untersuchung des Potenzials von Dahlem Cashmere Ziegenmilch für die Käseherstellung ausgelegt. Andererseits waren die in Wechselbeziehung stehenden Effekte von Homogenisieren, Mikrofiltrieren und pH auf die rheologischen Eigenschaften von labinduzierten Milchgelen, auf die Synärese und schließlich auf die Käsezusammensetzung, -ausbeute und Funktionalität zu untersuchen. Drei mathematische Modelle wurden auf ihre Eignung, die Synärese zu beschreiben, verglichen. Die kinetischen Parameter, die über ein linearisiertes Modell berechnet wurden, erzielten die beste Kurvenanpassung mit hohem Korrelationskoeffizient (r2 > 0.99), so dass dieses für die Berechnung der kinetischen Daten zu empfehlen ist. Darüber hinaus bietet das Modell mit dem Parameter RWRmax Informationen bezüglich des Maximalwerts der Synärese. Über diesen Wert können Aussagen getroffen werden, inwiefern die Struktur des Labgels und das Zusammenspiel von Milchzusammensetzung und physikalischer Faktoren die Synärese beeinflussen. Weichkäse wurde mit Streptococcus thermophilus und EPS-bildenden Stämmen von Lactococcus lactis subsp. cremoris und Lactobacillus sakei produziert. Die EPS-Bildner wurden in einem Medium angezogen und der Käsereimilch in Konzentrationen von 5 und 10 % (w/w) zugegeben. Die Zugabe von EPS-Medium verzögerte die Synärese und erhöhte die mikrobielle Fermentation, so dass Reifungsprobleme auftraten. Mit Hilfe von Modellversuchen bezüglich der Synärese und des pH Wertes wurde die Weichkäseherstellung technologisch angepasst. Die Vorgehensweise zeigte, dass die Weichkäseherstellung nun möglich und der Serumgehalt der Rohkäse durch den Zusatz von EPS-Medium erhöht war. Das Homogenisieren, MF und der pH-Wert beeinflussten die Synärese signifikant. Es wurde gezeigt, dass die Milchzusammensetzung und das MF den Endpunkt der Synärese, RWRmax, deutlich beeinflussten. Bruchkörner aus Magermilch hatten den höchsten RWRmax Wert. Da das Schneiden bei gleicher Gelfestigkeit erfolgte, wird angenommen, dass die Synärese maßgeblich durch die Verteilung und den Gehalt an Fetttropfen beeinflusst wird, woraus sich Unterschiede in der Mikrostruktur des Labgels ergeben. Die Versuche verdeutlichen, dass durch das Kombinieren von Homogenisierung und Mikrofiltration Gelfestigkeiten und Synäresewerte erzielt werden, die mit Werten aus der traditionellen Käseherstellung übereinstimmen. Die Kombination aus Homogenisieren und anschließender MF war bezüglich der Käseausbeute viel versprechend und aus den Ergebnissen und Erfahrungen, die in dieser Arbeit erzielt wurden, wurde ein neuer und vereinfachter Prozess der Schnittkäseherstellung erstellt. Die auf die ursprüngliche Milchmenge bezogene Käseausbeute und Rückhaltung von Inhaltsstoffen nahmen daraufhin auf Grund der Interaktion von Homogenisieren und MF zu. Die Kombination aus Homogenisieren und MF offenbarte sich als besonders viel versprechend für die Käseherstellung

Drainage of curd

Cheese making starts with transformation of the liquid milk into a gel by proteolytic enzymes and/or acid producing bacteria. The gel is cut into pieces. The protein matrix contracts, by which whey is expelled from the pieces, this process is called syneresis. The process of whey expulsion is enhanced by stirring and usually heating. Finally fairly rigid curd grains and a large amount of whey are obtained. The subsequent separation of whey and curd grains is called drainage of curd. For most types of cheese, the obtained curd mass is subsequently pressed, salted and ripened. This study is mainly aimed at the drainage in case of Gouda cheese, but some aspects may be applicable to other cheese types as well.Drainage of curd not only separates (most of) the whey from the curd grains, but it also leads to the formation of a coherent mass. The drainage is not an isolated process, but its outcome depends heavily on the preceding curd preparation and the subsequent shaping and pressing. The study of the drainage process therefore requires a well-controlled curd preparation. In our conditions large-scale curd production was often not possible, but scaling down of the curd making process led to curd grains that had only little resemblance to those produced on factory scale. A new way of curd preparation was therefore developed. It enabled the production of almost identical cube shaped curd grains. The basic features of the new apparatus were: the gel was cut in cubes by two wire grids, and the cubes were stirred by subsequently pumping an amount of whey and large air bubbles through holes in the bottom of the cheese vat. The delicate curd pieces were hardly broken up by the resulting gentle stirring. As the used air is toxic to starter bacteria curd was prepared without starter.The curd grains were characterized by measuring their density in thermostatted sodium chloride solutions of various concentrations. The density can be recalculated to a moisture content or relative remaining volume, i.e. the volume of curd grains as a fraction of its volume before syneresis. The density measurement could, in the case of uniform curd grains, replace the various empirical methods currently applied to determine the moment to begin with drainage. However, in case of factory made curd other factors may also be of importance, e.g. pH, temperature and the amount of curd fines.The uniform curd grains were used to study the expression and deformation of a single curd grain in a uni-axial compression setup. The compression led to an instantaneous (elastic) and a slower viscous compression of the curd grain. Release of the stress within a few seconds after the start of the compression led to a clearly visible recovery; this was not the case after 15 minutes of compression. The elastic and viscous compression increased with the exerted stress ( pm ) and initial relative remaining volume of the curd grain (i 0 ). The extent of compression increased with time ( t ). The relative remaining volume at time t of a single curd grain ( it ) could be expressed as:where ( ioo ). is the relative remaining volume at infinity and k is a constant (4.10 -5Pa -1.s -½). The expression also led to horizontal broadening of the curd grain. The broadening increased with the exerted pressure and decreased slightly with decreasing initial remaining volume of the curd grain. At maximum, the broadening increased the original cross-sectional area to about 1.6 times. The extent of compression and volume decrease of the curd grain appeared to be closely correlated. The rheological properties of the paracaseinate strands probably become soon after the start the rate-determining factor at expression. The resistance to flow of whey may be a rate limiting factor at the start of the expression. It was observed in CSLM photographs that the surface layer of the cube shaped curd grains showed cracks. In the outer layer of curd grains obtained from factory made batches no cracks were observed, but, after application of a stress, cracks were formed.The fracture stress of fused curd grains could be studied at constant macroscopic fusion area with a newly developed technique. The fracture stress was positively correlated with the fusion time and the exerted pressure. The initial remaining volume also showed a positive correlation with the fracture stress, within the small test range. The temperature also had an effect upon the fracture stress: the highest fracture stress was obtained at about 35 °C and higher or lower temperatures both led to somewhat lower values.The sedimentation rate of curd grains may vary due to differences in apparent weight and density, but the fact that small curd grains are usually found at the bottom of a settled layer of curd grains can not be attributed hereto. Small curd grains can, however, fill the gaps between adjacent larger curd grains. The cube shaped curd grains rotated when freely settling. Anisometric curd grains sank with their longest axes perpendicular to direction of sedimentation, regardless of their initial position.Due to preferential orientation of the curd grains and the deformation of curd grains the curd bed has to be considered an anisotropic medium. The flow of whey occurs mainly through the interconnected openings between the curd grains, and the permeability of the curd bed in the horizontal direction will be greater than that in the vertical direction.Various types of drainage equipment are used to perform drainage, depending on the scale of production, the variety of cheese produced and the cost/benefit ratio. Batch drainage systems are mostly used in small scale production units, whereas continuous drainage vessels are commonly used in bulk cheese production. Both types have been realized in several, somewhat varying constructions and also the mode of operation varies from plant to plant. It was tried to study the effects of various designs upon the drainage by the construction of small scale drainage vessels. Scaling down of the often applied batch drainage vessels could not be done adequately, as the leakage of whey between the vessel wall and the compressed curd column contributed significantly to the flow of whey. Vertical perforated cylindrical pipes were used as a model for the continuous drainage vessels. Obvious parameters are drainage time and temperature, whey discharge conditions, and duration and magnitude of the exerted pressure. Other relevant parameters are the pressure loss due to the friction of the wall and the leakage of whey between the wall of the vessel and the curd. The packing near the wall is less dense due to steric exclusion. The friction at the wall alters the orientation of the adjacent curd grains: the curd grains are turned to an acute angle to the direction of movement of curd column.Experiments with colored curd grains in a Casomatic drainage pipe showed that curd grains were slightly mixed at the top. The flow of curd grains through the pipe can be considered as a plug flow with a parabolic flow superimposed on ft. A trail of colored curd grains at the rind of the subsequent blocks was observed, these curd grains probably got stuck at the filter grids near the whey outlets.The compaction of a curd/whey mixture in the vertical drainage columns initially increased when the exerted pressure and/or the initial remaining volume of the curd grains increased. However, above a certain external pressure, called threshold level, the transport of whey out of the column becomes rate determining; the compression then is accompanied by a fast increase in liquid pressure. The threshold level is primarily determined by the curd properties, but the relations strongly depend on thedrainage vessel's properties. Whey discharge conditions, the contact area between curd and the wall, the exerted stress upon the curd grains and the drainage time are mainly determined by the drainage vessel. The packing of the curd and the extent of fusion are likely to be relevant, but were not extensively studied. The whey content and the firmness of the curd grains and the presence of curd fines had significant effects.Visual inspection of cross-sections of curd blocks made in a Casomatic showed pores in various sizes and shapes, the largest ones being about 5 mm. The curd blocks lost a considerable amount of whey after the drainage. This drip whey originated largely from the inside of the curd grains.The porosity of a curd column could be measured with a newly developed porosity meter. The working principle of the apparatus is a moving optical fibre that penetrates the curd bed. The difference in scattering properties of curd grains and whey in the pores allows discrimination between either. The porosity of a curd bed so estimated, showed a large standard deviation, as the number of pores was rather small. The porosity generally decreased in time, which was due to decrease in the number and in the (apparent) size of the pores. Significant effects of the initial relative remaining volume upon the porosity were not detected. The compaction of a curd column at an external pressure level below the threshold value resulted from the decrease of porosity as well as from the whey expulsion from the curd grains. In this case, the porosity did not differ significantly between the central part and the outer regions. A higher external pressure led to a faster decrease of the porosity. At an external pressure above the threshold level the porosity of the outer region became lower than that of the central part.The permeability of a curd block decreases over several decades during the drainage process. Initially the permeability is very high. The permeability is mainly determined by the interconnected pores, whereby the largest pores contribute most. The pores can become disconnected due to reorientation and deformation of the curd grains. Application of pressures above the threshold level finally do not result in further expressed curd columns, but cause jamming. The high pressure causes a substantial reorientation and deformation, hence, the permeability decreases very rapidly. The flow of whey from the central region becomes insufficient to keep up with the fast whey expulsion from the outer layer, causing a further decrease of the porosity in the outer region. This, in turn, retards further transport towards the outer layer, causing a rapid sealing near the rind.A simple computer model was made. The expression of a single cube shaped curd grain was used as a model for the expression of a batch of these curd grains. It appeared that the model gave reasonable results at low external pressures. At high external pressures the model was inadequate, as the transport of whey from the pores between the curd grains becomes a rate determining factor, and this factor is not taken into account in the model. In the intermediate pressure range the model predicted a too fast expression of the curd grains, although the overall liquid pressure was below the detection limits. The latter does not rule out the existence of isolated pores, hence the liquid flow may locally be retarded. The deformation of curd grains in a curd bed may also be retarded due to fusion and geometrical constraints

Styring av hvitost-kvalitet – strategier og metoder for å oppnå riktig sensorisk kvalitet på produktene ved forbruk

An effective approach to quality control is an important issue for a food producer, as consumers expect consistent delivery of products. Two important strategies for control of food product end quality was discussed in this thesis: Process regulation and Statistical Process control (SPC). Extensive experiments were carried out in order to demonstrate different aspects of control of cheese quality. The sensory quality of a product is of great importance, as it is directly perceived at consumption. How do we define, and measure cheese quality? In paper 3 this subject was discussed, and quality scoring was found appropriate as a methodology for sensory quality, provided consumer input in definition of product specifications. Rapid, particularly non-destructive measurements are important in control strategies. In paper 4 spectroscopic methods were found promising for fast and reliable results. Spectroscopy was found to be able to substitute chemical measurements for the purpose of measuring relevant sensory attributes of cheese. In paper 2 X-ray methodology, found suitable for non-destructive on-line measurements of eye formation in cheese during ripening, was developed. In statistical process control, SPC, it is essential to understand the influence of all relevant factors from raw material through process to product. In paper 1 the effect of variation through all seasons of the year, as well as the effect of maturation after different ripening temperatures on sensory properties of cheese was examined. This gives us a better platform for adjustments with the aim of variability reduction for the actual cheese varieties.En effektiv tilnærming til kvalitetsstyring er viktig for næringsmiddelprodusenter, da forbrukerne forventer levering av produkter med jevn kvalitet. To viktige strategier for styring av matprodukters sluttkvalitet ble diskutert: Prosessregulering, og statistisk prosesskontroll (SPC). Omfattende forsøk ble utført for å vise ulike aspekter av styringen av ostekvalitet. Den sensoriske kvaliteten til produktene er av stor betydning, da den blir direkte oppfattet ved forbruk. Men hvordan definerer vi og maler ostekvalitet? I artikkel 3 diskuteres dette emnet, og kvalitetsbedømmelse med poeng ble funnet å vare en metode som passer for formålet, forutsatt at resultater fra forbrukerundersøkelser brukes som grunnlag for produktspesifikasjonene. Hurtigmetoder, spesielt ikke-destruktive malinger, er viktige styringsverktøy. I artikkel 4 vurderte man spektroskopiske metoder som lovende for raske og pålitelige analyser av ost. Spektroskopi ble funnet å kunne erstatte kjemiske malinger I forhold til å måle relevante sensoriske egenskaper I ost. I artikkel 2 ble det utviklet en røntgenmetode som passet for maling av hullsetting I ost under modning. I statistisk prosesskontroll, SPC, er det grunnleggende å ha forståelse for innvirkningen av alle relevante faktorer, fra råmaterialer gjennom prosessen til ferdig ost. I artikkel 1 ble effekter av variasjoner gjennom året, og ulike modningstemperaturer undersøkt, I forhold til påvirkning på sensorisk kvalitet. Dette gir oss en bedre plattform for justeringer med henblikk på reduksjon av variasjon for de undersøkte norske ostetypene