Vacuum cooling technology has finally come to maturity and today presents itself with the support of new vacuum systems and sophisticated control systems as a technology of the future. Developed in Switzerland, the system is price-effective and increases quality.
Vacuum technology as such is nothing new. Vacuum cookers have been used for many years to gently deaerate and evacuate fruit preparations and flavors. What is new about the technology developed by Aston Foods Ltd in Rotkreuz, Switzerland is that it is employed in a complex process unit designed as batch and semi continuous systems; for example for baked goods. But it is not only about the cooling of baked goods. The entire baking process is redefined with this technology. The gelatinization of the starch and denaturing of the egg with are defined with the process.
- Left hand pre- baked and vacuum-cooled, Right hand: conventional product
Baking is basically a simple process: flour and water, in the form of leavened dough, are heated, causing the steam that is generated to expand the matrix of egg white and starch whereby the web of egg white coagulates into elastic strands and the starch wells. When it cools, the matrix forms a firm structure (bread crumb, bread crust). So far the principle: but as every baker knows, in reality this is somewhat more complicated.
Under vacuum, this formation of the structure can be controlled in a way not feasible with conventional baking methods.
The baking process requires a lot of energy: nearly a halve kilogram of water has to be evaporated per kilogram of bread. And the bread is hot when it is removed from the oven. This means one has to let it cool off. This does not only cost money for the industry (storage space, transport, working time, outlet air). The idea of cooling the bread was thus conceived a long time ago; even with vacuum. This, however, did not work very well, because baked goods tend to collapse, dry up or lose their flavor.
The Aston process ®
The Aston process® is characterized by the fact that a normal piece of dough is only pre-baked in a conventional oven and then, in a second step, is fully baked – hot – in a “pulsating” vacuum. In so doing, the baking time of a normal roll is reduced to 11 minutes. The baking time is actually only 9 minutes. The vacuum process takes 2 minutes. The baked good leaves the vacuum station at 25ºC; the crumb being fully developed. It can immediately be eaten or packed. It can also be quick frozen when necessary. Process control is demanding, but if performed correctly, the crumb of the baked good is considerably better compared to a conventional product. Pore formation is more homogeneous, there is an increase in pore volume of approximately 10% and the color of the bread crust is nicely varied. The water content of the product is approximately 7% higher. This means about 10% less dough is necessary for a commercial product. A nutritional and commercial advantage.
A welcome side-effect of the process is that the surface of the baked good no longer gets wet, because at 25 ºC the good is in moisture equilibrium. The process is therefore particularly well suited for baked goods with fillings which have a higher water content and increased water activity (aw value), such as strudel or brioche-type pastries. This is all the more true with these products because optimum dehydration of the centre is not possible with conventional baking methods. Due to the cooling of the vacuum process, the temperature range critical for microorganisms is quickly passed trough. The “fat layer” at the contact area between the filling and the pastry thus disappears. Deviations in taste are less likely and hygiene is increased. As result, shelf-life can be extended.
- Shelf-life prolongation through vacuum cooling.
What happens in the vacuum process?
The vacuum is lowered to a maximum of 10 mbar (hectopascal) during this process. This corresponds to a boiling temperature of 7ºC or air pressure at an altitude of 30000 meters.
The vacuum process parameters must be determined for each recipe. The vacuum is turned on in short intervals and is interrupted by short rest periods during which the pressure in the product can equalize again. Without this pressure equalization, the drag flow within the product would separate and the centre of the piece of dough could not be dehydrated. Instead, the flavor would be lost. The controlled drag flow thus dehydrates the centre of the baked good until the crumb is in state of equilibrium.
In addition to this, the process completes the unfinished gelatinization process of the pre-baked piece of dough. Furthermore, the process causes a partial micro-crystallization of the starch fraction which in turn results in a weak retrogradation. This step is unique in further stabilization of the baked good; analogous to the tempering of chocolate.
The appearance and stability of the crumb are improved and due to the increased moisture content of the baked good, this effect is perceived as something very positive. The elasticity of the crumb is also higher compared to conventional products. This point to the fact that the gluten is also conserved during the process and is less subject to denaturing.
Potential for savings
Apart from saving on flour, water and process energy, savings can be made from the operation flow, packing and logistics, all which make the process interesting:
Because the products leave the unit at normal temperature and moisture equilibrium, they often require less elaborate packing and logistics. Because with baked goods that are stable, aeration, cooling or quick-freezing are not necessarily required.
This means that under industrial production conditions, 3.45 to 5.0 cents can be saved over the entire process, including energy, packing, logistics and returned goods. Assuming a daily production of 36 000 rolls, this amounts to a considerable saving.
Vacuum cooling. The future for baked goods production.
– 30% shorter baking times
– Cooling in just 3 minutes
– Ready for immediate use
– Longer shelf life
– Greater process certainty
– Lower power consumption
– Enhanced quality
– Less shift work
– New sales channels
Ferré & Consulting Group, official advisers and consultants of the Iberian Peninsula (Spain and Portugal)