Formation of nitrogenated material in beer
A quick study on the nitrogenated part of beer, from barley to the final product.
The amount of protein found in the barley grain used in beer is around 10,0 and 11,5%. Of this amount only one third goes to the finished beer.
The malt extract content decreases with the increase of protein almost proportionally in barley grain.
Construction of proteins
All proteins are in the constitution of living organisms in the form of unbranched chains of amino acids. The sequence of amino acids in the chain is prefixed by building organisms. Protein formation may consist of up to 300 amino acids.
The proteins react both in acid and alkaline environment. Between acid and bases, proteins are neutral, their dissolution is very little.
The decomposed proteins are always soluble in water and do not coagulate when boiled. In the finished beer are kept only the “decomposed proteins”.
In proportion, the smallest part of protein in barley is decomposed, around 8%. This proportion increases in malting and mashing.
The high molecular weight decomposition products called Proteoses are the main foam formers and bring stability to it, but they can also bring turbidity to the beer. The protein decomposition occurs largely in malting.
The more dissolved the malt, more FAN will form between 45°C and 50°C in the mash vat.
When not using unmalted adjuncts and malt is well dissolved, a short rest at 45°C should be done.
A prolonged rest at 45°C always brings a less consistent foam.
Positive proteins for foam stability begin to form at 60-70°C in the mash vat.
There is no need of resting at 45°C for well dissolved malts.
Removal of nitrogenated material excess
In wort boiling all high molecular weight proteins are removed from the wort. The longer and more intense the boiling, more efficient this precipitation will be.
An important change that happens in the wort during boiling is the precipitation of nitrogenated material.
At the beginning of the boil the wort is transparent and soon becomes cloudy. During the boil, very thin and delicate proteins are transformed into particles of greater weight and volume and are precipitated to the bottom of the boiling vat. This precipitation is very important for the taste, body and stability of the beer. An insufficient coagulation may cause direct and indirect problems, such as the clogging of yeast membrane pores during fermentation and maturation phases.
The coagulation step occurs in two phases: The first one is of chemical nature, called denaturing. The second one, physical-chemical, is called Coagulation.
The ideal pH for protein removal at the boil is 5,2, which is almost impossible to achieve naturally, without the addition of acidifiers.
The first step of flocculation, when the boil is done properly, occurs completely. The second step does not always occur completely. Thus, frequently only part of the coagulable protein is removed, not occurring the formation of bigger lumps which precipitate easily. The longer the boil, the greater is the protein removal of the wort.
Picture 1 shows that the greater the evaporation in the boil vat, greater is the flocculation compared to the finished wort, but there is a point where the changes are not relevant.
When the boil is very intense, it is necessary to decrease this intensity 10 minutes before the start of Whirlpool for not breaking the flocs already formed during the boil. The heating steam is usually kept at the side of the boiling vat.
Removal of the hot trub
After boiling, the precipitate is now called hot trub, and it is formed mainly by nitrogenated particles . They are 30 to 80 microns big, which are heavier than the wort and in due time precipitate and go t the bottom of the vat.
The hot trub must be removed from the wort for being useless in the next brewing process steps.
Nitrogen for yeast
For the propagation and production of the cell wall the yeast needs nitrogen.
According to Narziss (2005), at the beginning of the fermentation the yeast hydrolizes peptides and then consumes them. But the main source of nitrogen for the yeast, whenever possible, is the amino acid, when there is enough of it in the wort. The yeast prefers amino acids over peptides.
At the end of fermentation the yeast assimilates peptides even if there are still amino acids in the wort. Amino acids are essential not only for the yeast propagation, but also for the formation of permeases and other enzymes. Thus, the wort needs enough amino acids and peptides for the yeast propagation and the smooth progress of
Cold turbidity: a bottle of beer is placed under ice water. After some time it turns out that the beer dipped in ice water is lightly clouded. The bottle of beer is removed from the ice water and its temperature is raised to 40°C, when turbidity disappears. After performing this cold/hot operation a few times the turbidity will cease to disappear, creating the Permanent Turbidity.
Permanent Turbidity: The cold turbidity becomes the Permanent turbidity after some time. It becomes visible even at higher temperatures.
Colloidal Turbidity Formation (proteinic)
The complex molecules of the beer are in motion, particles collide and over time they get bigger (a particle attaches to another, forming larger lumps) due to Brownian motion. Thus, particles increase and become visible. In this way the absorption links of proteins and polyphenols occur.