Here is the explanation of why chickpea tofu hardens. A common failure is that it does not firm up. This article will help you make it without failure.
Why Soybean Tofu hardens
To begin with, why does soybean tofu harden? The mechanism by which tofu hardens is protein denaturation. However, it is actually a very complicated process. For more details, please see this article.
Sesame or Peanut Tofu
How Chickpea Tofu Hardens
When treated with α-amylase, the viscosity hardly increased and no gel formed. When treated with trypsin, the viscosity increased slightly compared to when treated with α-amylase, but no gel was formed.
In this study, the fact that gelation of chickpea soybean milk did not occur when treated with trypsin as well as with α-amylase indicates that gel formation of chickpea curd is not only due to starch glueing but also to the involvement of protein.https://www.mame.or.jp/Portals/0/resources/pdf_z/098/MJ098-02B-TK.pdf
We will consider this in detail.
First, we will focus on the treatment with α-amylase. α-amylase is an enzyme that breaks down starch. So, if we read this part differently, it would read like this.
When treated with α-amylase, the viscosity hardly increased and no gel was formed.
When we break down the starch, the chickpea tofu does not harden.
This means that one of the reasons chickpea curd hardens is starch glueing. Starch glueing is explained in detail here.
Denaturation of Protein
Next, we look at the treatment with trypsin. Trypsin is an enzyme that breaks down proteins. So, if we read this part differently, we get this.
The viscosity increased slightly when the gel was treated with trypsin compared to when it was treated with α-amylase, but no gel was formed.
When we break down the protein, the chickpea tofu does not harden.
In other words, another reason why chickpea curd hardens is protein denaturation.
And based on this result, we can see the reason why chickpea curd does not harden.
Why Chickpea Tofu Does Not Harden
So far, we have understood the mechanism of chickpea curdling. Now we will consider the reasons why chickpea tofu does not harden.
Using Boiled Chickpeas
The first and most likely reason is that you used boiled chickpeas. There are two differences between raw/dried chickpeas and boiled chickpeas.
The first is the amount of starch.
Have you ever boiled chickpeas? If yes, you may have noticed that the boiled water bubbles. This is due to the starch in the chickpeas dissolving in the boiling water.
Second is the nature of proteins. Proteins change shape when heated. And it does not return to its original shape when cooled. This is called thermal denaturation of proteins.
When you boil eggs, the whites and yolks harden. This is due to this thermal denaturation.
Now, consider the case of chickpea tofu. Again, let me quote from the paper
In the present study, the fact that gelatinization of chickpea soymilk did not occur when treated with trypsin as well as α-amylase indicates that gel formation in chickpea curd is not only due to starch glueing, but also to protein.https://www.mame.or.jp/Portals/0/resources/pdf_z/098/MJ098-02B-TK.pdf
In other words, protein is responsible for the hardening. When you boil chickpeas, the protein is affected by heat denaturation. As a result, boiled chickpeas do not harden chickpea tofu well.
Blended Too Much
What if you use raw/dried chickpeas but they don’t firm up? That would be too much blnending. Here is a quote from the paper again.
Carbohydrate values were lower after 3 minutes of grinding time and as grinding time increased. On the other hand, moisture values increased. Gels were less likely to form as the milling time was increased.https://www.mame.or.jp/Portals/0/resources/pdf_z/098/MJ098-02B-TK.pdf
In this paper, experiments were conducted under four conditions: 30 seconds, 1 minute, 3 minutes, 5 minutes, and 10 minutes. It then reports that the longer the agitation time, the harder the gel formed.
They do not clearly state what causes the gel to be less likely to form. However, it is clear that the longer the stirring time, the harder it is to solidify.
Certainly, the more thoroughly you crush the chickpeas, the easier it is to squeeze them out. But if you run the mixer for 5 or 10 minutes to do so, it will cause not firm up.
Tips for firming
Now, let’s review the key points for firming chickpea tofu.
- Use dried chickpeas.
- Do not use boiled chickpeas.
- Use cold water to slowly rehydrate dried chickpeas.
- Do not over mix in a blender.
Here is a recipe for chickpea tofu based on this article, which is full of tips for success.