After having analyzed the most important ingredient (flour) that allows the structure, the color, the fragrance of the baked product, we now see what allows to generate the volume.
Erre4m friends good morning and welcome to this new post. Today we are talking about leavening! There are three types of leavening. Let's see them:
1. PHYSICAL LEVITATION is due to the thermal expansion of water in the form of water vapour and/or air bubbles, present inside the dough, during baking. In the first case, the water in the oven acts as a leavening agent, as the heat transforms it into steam which, trying to escape from inside the dough and finding the resistance of the flour gluten, pushes the product upwards, causing it to rise. In the second case, if the dough is prepared by acting on the whipping power of the egg proteins, which allows to store a high quantity of air bubbles, these bubbles expand during the baking, increasing the volume of the cooked product.
2. CHEMICAL LEVITATION basically used for pastry products, this leavening is obtained thanks to chemical agents, i.e. ammonium bicarbonate and sodium bicarbonate. These substances are able to generate carbon dioxide inside the dough. The CO2 bubbles in the oven dilate, causing the dough to rise. Ammonium bicarbonate produces CO2 during baking because it reacts to heat, while sodium bicarbonate produces CO2 when it comes into contact with water. It should be noted that sodium bicarbonate reacts much more in the presence of acid-based liquids; therefore, acid salts such as mono potassium tartrate are added to chemical leavening powders, which activate sodium bicarbonate to a greater extent
3. BIOLOGICAL LEVITATION in this type of leavening, the carbon dioxide is produced by alcoholic fermentation generated by microorganisms. The microorganisms suitable for organic leavening are found in compressed or dry brewer's yeast or natural yeast, also known as sourdough and sourdough. Biological leavening gives the baked product a rich and characteristic aroma.
Biological leavening is mainly used in bread making but also in all those leavened pastry products for breakfast as well as the wide range of large leavened products such as pandoro, panettone, doves, etc... This leavening, as it often happens, must have been discovered by chance in ancient times probably forgetting to bake the bread immediately after its preparation as it was commonly done. Certainly it was observed the greater softness, palatability and digestibility that the piece of bread had after it had been left to rest for a few minutes after being formed. The knowledge of all fermentation processes, however, remained unknown for many centuries. The baker limited himself to adding pieces of sour dough or beer sediments to the dough, capable of producing that spontaneous swelling of the piece of dough that made it incomparable softness and final taste. It was only at the end of the 1600s that the Danish optician Van Leeuwenhoek discovered yeasts and their "leavening" capacity by observing beer production residues under a microscope. The circle was closed in 1850 by Pasteur who studied the reproductive and fermentative mechanism of yeast cells, their ability to live both in the presence and in the absence of air and to transform sugars, necessary for their nutrition, into ethyl alcohol and carbon dioxide. The yeast most commonly used to obtain organic leavening is that of saccharomyces called Saccaromyces Cerevisae. Saccharomycetes are unicellular fungi.
Without going into excessively technical explanations, it is interesting to highlight some particularities of these yeasts that influence the preparation of bread. Under the cell wall there is a membrane that contains many enzymes necessary to receive and assimilate the nourishment for the life of the cell itself, that is glucose. As we can see also in yeasts the function of enzymes is fundamental let's see them:
1. INVERTASE breaks down the sucrose present in the flour into glucose (which is used to feed the cell) and maltose.
2. MALTASE demolishes maltose, already broken down by amylases, into two glucose molecules > food for the cell
3. ZIMASIS synthesizes glucose that feeds the cell with subsequent production of CO2 and ethyl alcohol > leavening
Another fundamental peculiarity for biological leavening is that yeasts live both in aerobic (presence of oxygen) and anaerobic (absence of oxygen) conditions; during kneading, the machines absorb a considerable amount of oxygen from the dough, so the yeasts, being in aerobic conditions, begin to reproduce by budding (i.e. the daughter cells detach themselves from the mother cell, generating a new cell equal to the previous one); once the yeasts have run out of oxygen and are therefore in anaerobic conditions, they begin to ferment. The reaction of alcoholic fermentation produces gas (CO2) with a consequent increase in the volume of the dough.
The most widely used yeast for the preparation of leavened products is compressed yeast, the soft yeast in loaves to be precise. It has a light beige colour, and its surface may have nuances that depend on its purity, degree of acidity and humidity. It has an insipid and slightly acidic taste due to the production base (the molasses) and the lactic bacteria it contains. Brewer's yeast is also marketed in an active dry form. The advantages of its use compared to compressed yeast consist in a longer shelf life and a higher yield; the use of dehydrated dry yeast allows the use of low doses which can be even half that of compressed yeast. The advice, therefore, is to test the various types of yeast to see which one suits our way of preparing savoury or sweet leavened products
500g strong flour W320
50g extra-virgin olive oil
15g compressed yeast
20g fresh whole milk
Final dough temperature 24°C
Stemper the yeast in the milk and mix with the flour and salt for 5 min at low speed Switch to higher speed (2-3) for a further 5 min to form the glutinous mesh, obtaining an elastic, shiny and smooth dough. Leave to rise in the bowl of the machine well covered at a temperature of 22°C for 2 hours. Break the dough into 60g pieces, give the desired shape, cover and leave to rise for another hour at 25-26°C. Bake at 220°C, sprinkling the surface with warm water and baking for 25-30 minutes, opening the oven door slightly for the last 10 minutes