The positive effects of drying pasta in high temperatures
by Luciano Mondardini, R&D Director, Pavan, Italy
The positive effect of high temperatures on the drying of pasta is a fact that can no longer be questioned.
Its use has improved the cooking quality and appearance of pasta made from soft wheat.
The mechanism, or at least the main mechanism, by which cooking quality has improved in soft wheat pasta is essentially due to the transformation that occurs in the protein chains when they are exposed to temperatures that enable coagulation.
It is known that the protein chains of soft wheat gluten in comparison to durum, are longer in length and behave less tenaciously when subjected to stress. This is supposedly due to a different tendency to be distributed in space and to form hydrogen bridges or in smaller quantity or with less potential. This generates a weaker glutinous network, less able to keep the starch wrapped when it, due to the effect of cooking in water pasta, swells and gelatinises.
The high temperature treatment, made in a phase where the protein chains still have enough water to be in their maximum development of hydrogen bonds, blocks this network with coagulation allowing it to make the most of its binding capacity.
In addition, it has been observed that in soft wheat the quality of pasta made with high-temperature technology relates more closely to total protein content than gluten content. It is as if the albums and globulins that do not form part of the glutinic complex, submitted to the rapid coagulation process in the initial drying phases, could make a significant contribution to the glutinic complex in the formation of a containment net.
Tests conducted at the Italian Cereal Institute
Here is an example of a report, drawn from the tests conducted at the Italian Cereal Institute in Rome for a quality provision of spaghetti pasta:
OJ= Overall Judgement values between 20 (very bad quality) and 100 (excellent quality)
TOM= Total Organic Material Organic material that is lost on the surface of a spaghetti, values from 1.4 (very good) to above 2.8 (very bad).
As we can see, the correlation found in the high temperature dryness is only related to the percent of proteins and not to gluten quality.
OJ = 13.29 + 2.42 * % protein + 1.57 * gluten quality manual method
OJ = 24.61 + 1.94 * % protein content + 0.03 * W
(Chopin alveograph W value)
TOM = 2.94 - 0.055 * % protein content - 0.058 * gluten quality manual method
TOM = 2.51 - 0.031 * % protein - 0.001 * W
(W value of the Chopin alveograph)
OJ = 40.50 + 2.04 * % protein content
TOM = 2.08 - 0.065 * % protein content
* re-elaborated from:
- D"Egidio M.G., Mariani B.M., Novaro P. 1993. Influence of raw material characteristics and drying technologies on pasta cooking quality: a review of our results. Italian Food & Beverage Technology. 1, 29-32.
- D"Egidio M.G. 1997. Influenza della materia prima sulla qualità della pasta. Molini d"Italia. 12, 15-18.
It is therefore very important to consider the quantity of total proteins, rather than the quality of gluten.
The practical application of these observations basically implies being able to achieve, within the shortest possible time, the peak temperature; furthermore, the higher the temperature, the more effective the treatment will be.
For this reason, in the Pavan lines the initial drying areas have a high thermal capacity and a large volume of air circulation.
Of course there are limits to this application, beyond the problem of not creating overly strong surface drying (case hardening) there is the problem of avoiding gelatinisation of starch from the surface of the paste.
For this reason, in the case of long pasta where the predrying conditions must be maintained with relatively high humidity, compared with what can be done in short pasta drying: it is very critical to be able to control the temperature, making sure it does not rise above 80°C before the pasta falls below 20 percent moisture content.
This is exactly what we are trying to do in our long pasta lines, which are designed, also in the pre-drying process, with the TAS method, with highly ventilated areas and resting areas.
This system allows us, without the risk of over-drying the product, to raise the temperature of the pasta more quickly than in other types of pre-drying plants where the pasta is always ventilated.
Under continuous ventilation, the surface part has a tendency to continuously lose water and to "overdry", therefore a minimal amount of heat can be supplied from the outside and, therefore, internal heat transfer proceeds more slowly.
With the TAS method, the strong heat transferred by the movement of air raises the outside temperature, which begins to transfer heat to the inside of the pasta. When it reaches the unventilated area, the heat is transferred internally while water can migrate to the surface, preventing the pasta from drying out only superficially.
This is why we are able to reach under 20 percent moisture content of the pasta in a shorter time frame and then rise above 80°C, optimising the effect of the very high temperature.
It is evident that very high temperature also means very high relative humidity.
For this reason it is absolutely necessary to create an area, in our case the final part of the predrying tunnel, where, when the paste reaches the maximum temperature, it is easy to have an environment with a high amount of water in the air in order to manage the required level of relative humidity.
The mechanical conception of this area, with the Separation Unit immediately after the tunnel, creating a plug to the internal air flow to the line and, on the other hand, the injection of air at the beginning, leads to a concentration in this area of all the necessary humidity.
Obviously, once the temperature peak has been reached, it is necessary to try to maintain a high temperature to maximise the effect, at least until the paste has enough humidity to avoid Maillard"s reaction. In Pavan Group"s drying system, where the treatment floors are separated and there are several temperature controls on each floor, it is possible to continue with temperatures above 90°C for more than half an hour after pre-drying. In these high temperature conditions the water mobility inside the paste is the maximum attainable, which allows it to reach a stable condition more easily and quickly.
The concept of drying with TAS technology is also important in the final drying section.
The possibility of modulating the amount of heat, which is essential to keep the water moving, allowing time to rebalance the humidity, is extremely important.
The constant technological evolution pursued by Pavan Group has led to further optimisation of the TAS drying process with a new production technology called Multidrive. This solution uses the very high air temperature (above 100°C) at the beginning of each drying phase. Multidrive technology is based on a continuous control of thermos-hygrometric conditions, by the application of a very high gradient of temperature increase and decrease rates, an optimised exhaust air extraction and a Multiple Pulse Ventilation system.
The result is an evolution of the well-known Pavan Thermo Active System technology: this long established product is excellent in terms of stability, structural strength and cooking quality. Furthermore, Multidrive allows for the control of colour change due to the Maillard reaction.