Extruded bread chips, possibilities and limitations - long version
In contrast to other direct expanded products cut at the die, extruded bread chips are cut not before the expanded dough has cooled down and hardened a bit.
In order to be able to expand an overheated dough at the outlet of the die into a well-shaped strand, the dough has to be kept under a defined pressure in the die that is bigger than the steampressure.
Typical dough temperatures of 160-180°C therefore request a minimum pressure of 6-10 bar. The expansion into the thickness of the strand gets stronger the bigger the die pressure is.
If you now choose a large die opening to get the most possible thick strand, it results in a low die pressure and thus the risk to go below the minimal pressure to avoid expansion already in the inside of the die. Consequently you get a worse shaped, torn strand with a rough surface.
This is why the minimum capacity necessary for keeping the die pressure and depending on the die is not allowed to be underrun concerning the manufacture of bread chips.
You may increase the die pressure cause of the high viscosity of a dough (low moisture) and therewith support the expansion into the thickness. A dough with a low moisture hardens very quickly, has therefore just a low shrinking and advantage for shaping thick strands. But a low moisture leads to the creation of a very soft texture far away from the actual “roasted bread” texture. High-viscous doughs have a lower elasticity and this is why there are considerable tensions/frictions in the product already during the expansion (in statu expandii). These tensions/frictions lead to a tearing off of the strand surface and the creation of an uneven poring/texture.
To get a crunchy, coarse, even texture that comes close to the texture of roasted bread, you have to extrude with sufficient moisture (17-20%). The dough stays soft and elastic after the expansion for a relatively long time at this moisture level.
Cause of the softness of the dough the cutting machine has to be positioned relatively far away from the die to reach a sufficient hardening of the strand before the cut. The elastic characteristics of the dough, however, also lead to a considerably higher shrinking due to the atmospheric pressure, means the decreasing of the strand diameter.
The use of whole-meal raw materials with the corresponding portion of evaporation nuclei in the manner of crushed fibre particles reduces the bubble size, makes the texture more even, but decreases the expansion into the thickness.
Based on this fact Schaaf Technologie has set the goal that besides the simple round bread chips also more complex shapes should get possible with this cutting technique and open pores. The product size, means the diameter of the individual “bread disc”, should also be maximized.
Schaaf has succeeded in extending the limits and to develop a completely independent product family of bread chips and consequently supplement the traditional bread chips shape by using new die designs and shaping machines.
A wonderful tasty in-between (snack) meal with cream cheese or sausage!