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The Dairy Science and Food Technology (DSFT) website provides scientific and technological information, Cloud-based tools and consultancy services for food scientists and technologists working in industry and in colleges and universities. A discussion forum and interactive content through "On Line" calculators are also provided. Writing/citation resources including a Harvard-type reference wizard and a range of citation-wizards can also be accessed.
There are sections on starter cultures, probiotics, cheese science and technology, bioactive peptides, ice cream, wine making, modelling in food technology, thermal processing and modified atmosphere packaging and labelling. Some general health information including reference to allergy and food intolerance is also presented.
The use of high temperature short time heat treatment (HTST) of milk (72°C for 15 seconds) to destroy pathogenic bacteria, reduce the number of spoilage organisms and increase shelf life is well established (Juffs and Deeth, 2007).
The history of pasteurization (pasteurisation is also valid) is fascinating and is notable for its public health success and for the insights of many scientists and engineers. Prior to the introduction of pasteurization, consumption of raw cow milk was a major source of infection by bacteria causing tuberculosis. Pasteurization has eliminated heat-treated-milk as a source of infection. Regrettably raw milk and raw milk products remain a major source of new cases of bovine tuberculosis.
In this article we will explore how to use mix composition to control the hardness or "scoopability" of ice cream or gelato. The serving temperature which influences the concentration of ice present will also be considered. The volume of air added during freezing (overrun), the manufacturing process and the concentration and type of emulsifier can also affect hardness.
However, these effects are generally less significant than the concentration of sweeteners used and serving temperature. This article should be read in conjunction with the article on the sweetness of ice cream. A condensed version of this article is available in the Food Science and Technology OnLine Journal (Mullan, 2018).
This article discusses the origins and role of starters in dairy fermentations, the ecology of starter bacteria, the classification of starter bacteria, the types of starter culture used and concludes with some observations on artisanal cultures. The author has provided a broader perspective on the use of starter cultures in food fermentations in the Encyclopedia of Food Microbiology. The chapter can be downloaded from Elsevier Ltd. This article should be read in conjunction with the article discussing the major functions of starters in dairy fermentations and the relative importance and effectiveness of the antimicrobial agents produced by starters.
This article discusses the major functions of starters in dairy fermentations. Recent research on the relative importance of the antimicrobial agents produced by starters is included. The importance of undissociated lactic acid (HLac) is discussed with regard to the inhibition of the growth of Listeria monocyotgenes, Escherichia coli and Staphylococcus aureus.
The author recommends that regulators should require manufacturers of raw milk cheeses to meet a minimum value for HLac that must be achieved prior to product release for retail sale.
These products are similar but can differ markedly from each other e.g. traditional Italian gelato is significantly different than mass produced, commercial ice cream in Ireland, GB and the US. However, high end artisan produced ice cream made using batch processes can be similar.
Traditional Italian gelato generally contains around 8% milk fat, has a low overrun usually (< 18%) and is served from a cabinet held at around -11°-12°C. The physical properties are usually different. Because of the higher temperature of storage and the concentration of sugars, gelato is served and eaten in a highly viscous, semi-frozen state. The texture is often described as being smooth and dense. Fruit-flavoured gelato is also characterised by intense natural fruit flavours and is quite sweet although natural fruit-like sour notes may be evident.
Traditional gelato is produced using batch production methods and is generally consumed within a short time from manufacture.
While there are differences between these products the scientific principles that underpin their production are similar and in the articles that follow, I will often use the terms ice cream and gelato interchangeably. Please accept that I do not equate the quality and eating experience of traditional Italian gelato with mass-produced commercial ice cream.
Refrigerated storage of raw milk is used to limit the growth of microorganisms in milk prior to processing. It has been known for some time that the quality and yield of cheese produced from bulk cooled milk may be adversely affected by this procedure (Weatherup et al., 1988; Weatherup and Mullan, 1993). The reduced yield and poor quality may be due to physico-chemical changes in the state of several milk components e.g. dissociation of micellar casein, mainly Κ-casein into a soluble phase, occurs during the first 48 h of storage at 4° and 7° C. This results in losses of fat and curd fines, weaker curd, more moist curd and a slightly lower yield. Partial reversal of dissociation occurs after further storage. The reduced yield and quality can also be due to the activity of proteases and lipases produced by psychrotrophic bacteria.
Despite the work that has been done over many years milk is still being stored for extended periods (1-3+ days on some farms) and cheesemakers are again (2019) reporting problems with the yield and quality of cheese produced using this milk.
Following several queries related to milk quality and cheese manufacture I am providing a report written by Wilf Weatherup and me some years ago that may be helpful.
A simple calculator has been provided using the total viable count of milk prior to pasteurisation and a regression equation to predict the grade value of Cheddar cheese.
I get lots of queries from companies and individuals either requesting recommendations for people who might be suitable for dairy science, dairy technologist, food technologist jobs or for advice from food job seekers on vacancies in particular job areas. I regret that I can no longer respond directly to these queries, I simply do not have the time to do so.
This article investigates how to calculate the lethal effects of UHT treatment and the usefulness of TTIs for differentiating sterilised, direct and indirectly processed UHT-treated milk. The importance of accessing accurate temperature time-data and knowing holding tube dimensions, flow rate, average and minimum holding time and the flow characteristics (Reynolds number) are discussed. The reliability of a model developed by Claeys et al. (2003) to predict the effects of UHT-processing on hydroxymethylfurfural, lactulose and furosine concentrations in milk is discussed. Free On Line calculators for calculating holding time, average flow rate, holding tube length in UHT and HTST plants are provided. A free On Line calculator programmed using the thermal constants calculated by Claeys et al. (2003) is provided to calculate hydroxymethylfurfural, lactulose and furosine concentrations following heat treatment in skim, semi fat and full fat milks. This calculator also calculates F0, B*, C* and % destruction of thiamine. Two methods of numerical integration are used to measure the cumulative lethal and chemical effects of UHT treatment, namely the Trapezoid and Simpson's rules.
Typical UHT treatments involve heating milk to 137℃ to 150℃ in a continuous-flow process and holding at that temperature for one or more seconds before cooling rapidly to room temperature. The milk is then aseptically packaged to give a product that is stable for several months at ambient temperature.
In Europe, UHT treatment is defined as heating milk in a continuous flow of heat at a high temperature for a short time (not less than 135 °C in combination with a suitable holding time, not less than a second) such that there are no viable microorganisms or spores capable of growing in the treated product when kept in an aseptic closed container at ambient temperature (Reg EC 2074/2005).
Why is the freezing curve of an ice cream or gelato mix important?
Freezing curves are useful in developing new ice cream and gelato products and predicting the hardness of the ice cream produced from particular mixes at designated temperatures, including the serving temperature. Curves can also be used to predict sensitivity to heat shock, storage stability and resistance of packaging materials to deformation during distribution and storage.
Many students have problems in understanding the mathematics describing the destruction of microorganisms by heat. Log reductions of pathogens and equivalent time-temperature treatments along with the associated lethalities account for a large part of the harder to understand topics. The quiz below is a simple test of of some of the basic concepts. Note Z value is not dealt with in this quiz. If there is sufficient interest I will provide the answers.