In the liquid food industry the demand for better quality at acceptable cost is forcing the processing industry towards new innovations.
Low temperature processing is one such innovative process.
Refrigeration technology has opened the gate for developing freeze concentration (FC) technology.
By using the latest refrigeration developments new concepts are being created that make freeze concentration more competitive with traditional concentration methods.
Food liquids consist of water and dissolved solids.
In most cases the water content is 90% or more.
Part of this water can be removed by concentration.
The advantage of using freeze concentration is that the original characteristics of the product are maintained as:
- low temperature processing prevents heat damage
- efficient separation of the water in the form of pure ice crystals prevents loss of aroma or dry matter.
The concentrated product has the same basic quality as the original.
Therefore, the success of freeze concentration is based on quality preservation.
Separation
Freeze concentration consists of two parts: crystallisation and separation.
During crystallisation, part of the water is converted into spherical and pure ice crystals without any inclusions.
Traditionally, a separate nucleation and growth principle is used to create these spherical ice crystals.
One of the new developments is to use slurry crystallisation in which the production of ice crystals and their growth is no longer separated.
The separation of the ice crystals is done in a piston type wash column.
In this wash column (Fig 1) the concentrated liquid is separated from the ice crystals by mechanical force (filtration) while the ice crystals are counter currently back-washed.
The pure separated ice is melted practically without any losses.
The positive effect of slurry crystallisation is in the design of the equipment and the manufacturing cost can be considerably lower.
In particular, the design of the scraped heat exchanger and mixing vessel can be simplified.
In combination with modifications in the ice separator cost compared with the rational design are significantly lower.
Additionally, the specific energy consumption is also less which results in lower overall production costs.
Niro’s newly developed IceCon process of slurry crystallisation reduces capital cost of the process by up to 40%.
Slurry crystallisation
In the Niro freeze concentration system slurry crystallisation combines an external heat exchanger with a mixing vessel to provide for necessary residence time for crystal growth.
The recirculation flow controls the sub-cooling and keeps the crystals suspended.
During the recirculation cycle the sub-cooling is transferred into ice crystals.
The level of sub-cooling will continuously decrease until its lowest value is reached shortly before re-entering the heat exchanger.
A cyclic pattern of sub-cooling will result.
Another important design aspect is the slurry density.
With proper ice concentrations and providing that proper mixing is assured there always will be sufficient crystals at all places within the mixing vessel to prevent primary nucleation.
The heat exchanger is designed with a scraped surface.
Fig 2 shows grown ice crystals that were formed in a concentrated sugar solution.
The freeze concentration process can be used for virtually every liquid with a low to medium viscosity.
The main advantage of preventing quality loss makes the process ideal for high quality, heat sensitive food products such as coffee extract, fruit juices, wine, beer, vinegar, dairy products and nutraceuticals.
The advantages of freeze concentration to the food industry are attributed directly to the distinct improvement in quality over existing products, while slurry crystallisation provides a significant overall cost reduction that will challenge quality oriented liquid food markets.