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Diffusion and Spherification: Science and Cooking

I’m excited to be starting this module with Gelatine because I’ve decided to make a layer cake next week. I’ve been trying to get my frosting game up to the level I really want it to be. I’m not a baker. I don’t like baking also. But I just cannot stand the fact that I’m not remotely good at it so I keep practicing it all the time. I’ve been looking up crazy types of frosting specially Italian buttercream frosting by PreppyKitchen and it looks so so good! But I’m honestly terrified to make it so as always I have my last and always handy whipping cream option. My mother has been churning butter at home for some while, turns out it is very easy to make whipping cream out of the malai the comes out of the milk. So I’m planning to do that as a back-up but I also cannot seem to find any Gelatine nearby. Enough, random ranting. Should probably start compiling my understanding of what this module is.

Gelation:

Gelation is a common phenomenon in cooking. Gel is formed by polymers (molecules composed of numbers individual units called monomers), strands that are next to each other in a solution and you usually have a mesh of these strands that are interweaving together. When these polymers overlap, you stabilise the crosslinks between these strands. When this happens what was initially a liquid (the polymers usually flow by each other into a solid) and if the crosslinks become high enough it becomes a gel. There are two types of Gels:

  1. Proteins that unfold because of the heat and stick to each other forming new bonds

  2. A binding agent that makes polymers stick to each other.

Polymer systems in water are called hydrocolloids, some are agar agar, cornstarch, gelation. An example of this is Chef Jose Andres Corn on the Cob.

What makes proteins stick so they can form gels?

Proteins are polymers, chains of amino acid (there are 20 kinds.) Amino Acids have different properties with different chemical and physical properties. They have two types of physical properties:

  1. Hyrdophilic: Likes water. If you have Hydrophilic+Hydrophyllic acids they will be happy tougher.

  2. Hydrophobic: Dislikes water. It also dislikes Hyrdrophilic amino acids because it likes water. If you have a protein of hydrophobic amino acids+ hydrophobic amino acids they will clump together. 

The phenomenon of Entropy is very much present. when the temperature of a system increases the average motion of molecule increases. Proteins unfold at higher temperature. When the temperature is low, the Hydrophobic ones are inside of a folded protein and the Hydrophilic ones shield it from water. At high temperature, the protein unfolds. and the Hydrophobic amino acids are exposed and start sticking to other Hydrophobic amino acids causing binding and cross-links which forms when you cook, e.g. an egg.

pH and Proteins:

One way to cook proteins and make them unfold require changing the pH like I wrote about in Module 2. Taking an egg, it can be cooked in two ways: by salt concentration or changing the pH.

For example, when making poached eggs, recipes requires 1 tbsp for 4 eggs and it is to be cooked for 2-3 minutes. By add vinegar you are changing the concentration of hydrogen ions in your solution (pH). Like we have discussed there are two types of properties that proteins have, Hydrophilic and Hydrophobic but something that is also important is that amino acid also has charge. Some have negative while some have positive. Like charges repel each other while opposite charges attract each other. One way of controlling the folding and unfolding of your protein is to change the charge when they are in a solution, that is changing the level of pH. Amino acids change their charge according to the pH in a solution. So if we make the charges more dramatic can easily unfold by changing the solution into an acid or base. However, the thing about changing pH is that we have to be careful of the taste, unlike when we change temperature.

Effect of pH on amino acids:

How does pH affect food? Well, it turns out that these protons will be attracted to more negatively charged molecules. Gaining protons can affect the chemical properties, for example in amino acid glutamate, proteins at neutral pH has a charge of negative one. When you lower the pH using acid, positively charged protons will be attracted to the negative charge, and attach themselves through a covalent bond neutralising the charge. This affects the Polarity of the atom. If that happens to a glutamate, that is in a protein it will affect the interactions of glutamate with other amino acid in the protein. Charge charge interactions between positively charged proteins and and negatively charged protein will be weaker if the acid is added since it looses its negative charge. If amino acids loose their charge causing iconic bonds to break, total number of interactions keeping the protein folded will start to decrease. And there will be an unfolding that will case the amino acid to break. This why sometimes we see cooking happening in acids.

Spherification:

Came about in 2003, by Jose Andreas. It when liquid is submerged into calcium alginate and goes into a water bath of calcium chloride. The alginate was now yogurt, that had calcium on calcium chloride water bath.

We can take a ball of juice, mango juice.  We take it add alginate into it (that will have negatively charged ions that don’t like each other much) Then take the ball and put it into a calcium bath which is positively charged, it moves into this sphere and starts to cross-link the gel which cause the gel to stick to itself and a thin layer of gel is formed.

However why does when sperification happen does the ball not become a complete solid. It is probably because it takes time for molecules to move through an environment without being mixed. We can define the amount of time it takes for molecules to move though a system and how certain molecules will travel this is through Random walks.

Random walks was discovered by Karl Pearson who wrote a journal in 1095 called the problem of the random walk in which he asked the readers about a random walk. Suppose you had a coin, you flip it and its a head you step to the right and if you get a tail, you step to the left. This random process of moving to the right or left is called random walks. He asked what the mathematics of this process was. Einstein had already written a paper in 1094, from what I understood what he said that if suppose, I am fat globule whether I move to right or left depends on the other gobbles on the either side of me pushing me from the right or left. What he later on proceeded to do was calculate the size of molecules. Another person who answers this, was Louis Bachelier, and the movement of stock prices and how it goes up and down. He said that random walks was like how stock prices moves. And his mathematical formula was similar to Einstein.

We can apply to this food, imagine if I am a calcium molecule which is going to be a bath in which a specification will happen to mango juice and alginate. How far does the calcium move, what is the distance it gets to reach them to get to sperification? This is what will give us the thickness of the gel. The answer is:

L2 = 4Dt

L= diffusion distance

D- diffusion constant

t= time

This applies to make cheese, vinegar, temperature thats trying go change heat of steak.

Diffusion for calcium in water is 8*10^-10 m^2/sec

Osmosis:

Osmosis is a process that causes salted meat to dry. Another thing can be coleslaw. Cabbage is 93 percent water and draws the moisture out in coleslaw. Osmosis occurs when mixed with salt, there is a semipermeable membrane in cabbage in which water can diffuse through, there will be an in crease in flux towards where the salt is added to the cabbage.

Dehydration:

Osmosis is very slow, if you salt your meat, it will take a very long time dry. This happens even if you leave it in the fridge uncovered. A dehydrator takes water out of food, it takes intensifies the taste, like raisins. Another reason, is for preservatives. Dehydrator heats up the food, but it doesn’t cook it it dries the water. They have blowers that blows hair and water molecules are swept away instantly.

Rapid Infusion:

An infusion is made by allowing a porous substance – herbs and spices – to steep in a liquid for long periods of time. When they contact the liquid, flavor molecules will slowly diffuse out of the plant matter and into the liquid. It takes a while for liquids like water to diffuse through a food – and then a similarly long time for the flavor molecules to diffuse back out.

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