Freeze Drying - Articles and news items

Freeze-drying in the coffee industry

Issue 2 2015  •  23 April 2015  •  Davide Fissore, Department of Applied Science and Technology, Politecnico di Torino

Freeze-drying is a process used in food processing to remove water from foodstuffs, with the goal of increasing their shelf life. The process consists of various steps: At first product temperature is lowered, usually to about -40°C, thus causing freezing of the free water. Later, the pressure in the equipment is lowered and sublimation of the frozen water occurs (primary drying). Finally, the bound water is removed from the product, usually increasing product temperature and further decreasing the pressure in the equipment, thus reaching the target value of residual moisture (secondary drying)…

Current advances in food freezing

Issue 5 2014  •  27 October 2014  •  Christian James and Stephen J. James, Food Refrigeration and Process Engineering Research Centre, Grimsby Institute of Further and Higher Education

Frozen food is one of the largest sectors of the food industry and its value is increasing throughout the world. The frozen food market in seven of the major Western European Economies was valued at €83.51 billion in 2013 and is expected to grow in value by 10.89 per cent by 2016. The market is broadly segmented into frozen; vegetables and fruits, potatoes, ready meals, meat, fish/seafood and soup and more than 35 per cent of this market is in the frozen ready meals sector. In a previous article for New Food we discussed different innovative freezing technologies for foods. Apart from impingement, many of the technologies discussed are still in development. In this article we will look at proven technologies…

Lyophilisation: Atmospheric food freeze-drying: challenges and opportunities

Issue 6 2013  •  2 January 2014  •  Davide Fissore, Mauricio M. Coletto and Antonello A. Barresi, Department of Applied Science and Technology, Politecnico di Torino

Freeze-drying is a process that can be used to remove water from foodstuff, thus increasing their shelf-life, avoiding deterioration of aroma and flavour compounds as well as nutrient degradation. In a vacuum freeze-drying process, product temperature is firstly decreased in such a way that all the free water freezes, then the product is exposed to low pressure and the ice sublimates (primary drying). At the end of the sublimation stage, the amount of residual water can be further decreased by removing the bound water (secondary drying); this stage is generally carried out increasing product temperature and decreasing the operating pressure. This way, all the characteristics of the product, e.g. shape, appearance, colour, taste and texture, are retained in the final product. Moreover, the high specific surface area of the final product allows a fast and easy rehydration…

Application of vacuum in the food industry

Issue 5 2012  •  6 November 2012  •  Frank Moerman, European Hygienic Engineering & Design Group and Nico Desanghere, Sterling Fluid Systems

Vacuum allows processes to be performed that cannot otherwise be done under atmospheric conditions. Moreover, it offers a huge advantage in the processing of heat and oxygen sensitive materials. There are numerous applications in the food industry that rely on vacuum. The vacuum required in the food industry extends in the range of 1-600 mbar vacuum absolute (vacuum pressure measured relative to absolute perfect zero vacuum), and is applied in the transport, processing, filling and packaging of foodstuffs, in cleaning operations and in the creation of appropriate hygienic conditions.

‘Sous-vide’ is the French word for ‘cooking under vacuum’. This cooking method aims to maintain the integrity of ingredients by heating them for an extended period (usually 8 – 10 hours, sometimes well over 24 hours) at relatively low temperatures (usually between 60-70°C) and pressures of 50 – 250 mbar absolute (40 – 60 mbar lower than the vapour pressure of water at a given temperature, Figure 1, page 68. But, there are cooks that prepare food ‘sous vide’ at temperatures as low as 55°C. However, for food safety reasons, that practice is not really recommended. After vacuum cooking, the food should be held at 55°C or above until served for immediate consumption, or should be rapidly cooled to below 3.3°C. A water ring pump is used to produce the absolute vacuum pressures required.

Innovative freezing technologies for foods

Issue 4 2012  •  6 September 2012  •  Stephen J. James & Christian James, Food Refrigeration and Process Engineering Research Centre, Grimsby Institute of Further and Higher Education

Freezing is a well-established food preservation process that produces high quality nutritious foods that offer the advantage of a long storage life. However, freezing is not suitable for all foods and freezing does cause physical and chemical changes in many foods that are perceived as reducing the quality of the thawed material.

There is a general view that fast freezing, and the formation of small ice crystals, offers some quality advantages. However, this is not true of all foods. For example, while freezing rate may affect drip in meat there is no evidence that it has any substantial influence on its final eating quality. Nevertheless, many innovative freezing processes are currently being researched and developed across the globe to improve freezing times and product quality.

Some innovative freezing processes (impingement and Hydro-fluidisation) are essentially improvements of existing methods (air blast and immersion, respectively) that by providing far higher surface heat transfer rates than previous systems, aim to improve product quality through rapid freezing. In these cases, the advantages may depend on the size of the product, since the poor thermal conductivity of many foods limits the rate of cooling in large objects rather than the heat transfer between the cooling medium and the product.

The optimisation of freeze drying processes

Issue 4 2011  •  6 September 2011  •  Javier Silanes Kenny, Associate Principal Scientist, Soluble Coffee Process Optimisation, Kraft Foods

From its infancy to today, lyophilisation has seen a constant but very slow evolution. Indeed, the techniques that we utilise today differ very little to those used industrially, after its development as a viable technique for the preservation of serum during World War II. Its application to pharmaceuticals and from there on to foods at commercial scales followed in very short order, becoming pervasive through the 1960s and 1970s to almost exemplify human progress in people’s imagination as the food of the space age in the 1980s.

In fact, it would be tempting to say that almost everything that can be invented in freeze drying has been invented, and that any small tweaks that developers today can think of are merely that: tweaks. Where, then, does that leave the technologist or engineer faced with the problem of reducing costs in the very expensive world of freeze drying? In a world where commodity, energy and food prices soar and where our consumers are ever more aware of the environmental impact of what they consume, the competition for the most cost effective and sustainable processes is won or lost in the ability to make those tweaks and to successfully implement them, and the full understanding of the science of the process becomes ever more important.

The benchmark in quality for dehydrated food products

Issue 3 2010, Past issues  •  30 June 2010  •  Daniel Donhowe, Expert Engineer, Nestlé PTC Marysville

Freeze drying is considered the benchmark in quality for many dehydrated food products. But is it worth the higher cost compared to cheaper air drying technologies such as spray or fluid bed drying? Freeze drying is a process that usually provides several benefits over competing technologies, such as improved flavour and aroma, better retention of nutrients (vitamins, bioactive compounds, etc), ‘natural’ or attractive shape, more natural colour after rehydration, better rehydration – especially for large pieces (e.g. fruits and vegetables) and better solubility for larger particles (e.g. instant coffee).


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