Dr. Alessandro Ippolito – Quality Manager
In recent years, many innovative technologies have been developed in the food industry to produce functional foods or to make safe products that are made available to the consumer. Among these is Vacuum Impregnation, a nondestructive technology by which a solution can be introduced into a porous matrix.
How it works
This technology makes it possible, through decompression cycles, to fill the intracellular space of tissues, changing the physicochemical and sensory properties of products. It is possible, for example, to change the moisture content, pH and aroma of a food or, in other situations, to add bioactive compounds to the matrix. The process consists of two main stages: the pressure reduction stage and the return to atmospheric pressure stage. Impregnation of the material occurs as a consequence of two phenomena: the hydrodynamic mechanism (HDM) and deformation-relaxation phenomena (DRP), which lead to the filling of intracellular capillaries (see Figure 1).
After the material is immersed in the solution (t0), the pressure inside (pi) and outside (pe) of the capillary is equal to atmospheric pressure (pi = pe = pat). Initially, the capillary volume (Vg0) is filled with gas (see Figure 1 – Step 0). In the first step of the process, the pressure is reduced (p1 < pat).
Due to the pressure difference, the gas is removed from the capillary, and the reduced pressure, acting from the outside, causes deformation and expansion of the capillary, which is the first part of the deformation-relaxation phenomenon (DRP). As a result, the volume of the capillary increases (Vg1A = Vg0 + Xc1).
This phase continues until pressure equilibrium is reached (pi = pe) (see Figure 1, Step 1A). Next, the capillary begins to be partially filled with liquid, due to HDM (Radziejewska et al., 2014). During this step, the pressure inside the capillary increases slightly, while the free volume inside it decreases to the value Vg1B = Vg0 + Xc1 – Xv1 (see Figure 1, Step 1B).
In the second phase of vacuum impregnation, the pressure returns to the atmospheric value. This causes the deformation-relaxation phenomenon (DRP) to transition to the relaxation phase. In this phase, the capillary shrinks further from its initial size before the start of the process. At the same time, due to the action of capillary pressure and decompression, there is an intense inflow of fluid from the outside to the inside of the capillary. The result of this process is a decrease in the final gas volume inside, as described by the formula Vg2 = Vg0 – Xc – Xv (see Figure 1, Step 2).
Practical applications
In the world of spirits, this technology is gaining ground with the introduction of special woods, such as oak chips, which are treated to acquire a wide range of aromas. You can find chips with notes of cherry, vanilla, green apple or even black pepper.
Through our laboratory tests, we have discovered the great versatility of these products, which can be added during the aging phase of wines (both white and red) or in spirits such as gin, vodka and rum, before distillation or bottling. This allows the bouquet of flavors and smells to be emphasized and enriched.
In conclusion, we can say that this innovative technology can play a significant role in both the food industry and alcoholic beverage production, creating new products to meet growing market demands.
