I had soaked some soybeans and kept them in the fridge for two to three days after removing the water. Today, I kept the mixture after blending with water for 3 hours. However, when I kept it on a high flame it curdled.

The recipe was-

1)Take a cup of soaked soybeans.

2)Add three and a half times the water and blend for 3 minutes.

4)Cook the mixture after boiling for 15 minutes.

5)Strain the okara using a cheesecloth enter image description here

Will this thing be edible after cooking? What caused this curdling?

  • It this the first time you've attempted soy milk? Have you had success in the past?
    – moscafj
    Dec 5, 2020 at 13:19
  • No, I have made it before many times with absolute success.
    – Arrowroot
    Dec 5, 2020 at 14:04

1 Answer 1


There are two potential causes here - either positive ions or bacterial activity.

Soy curdles easily in the presence of positive ions, that's the basic principle behind making tofu. I don't see many potential sources in your recipe, so if this is the case, my guess would be that there was some combination of hard water, possibly high-ish magnesium levels in the soy itself, and maybe some other deviations in the soy chemistry (not every cultivar or every batch of the same plant is equal chemically, and if you hit the right - or in this case wrong - combination of compound levels, curdling occurs easier).

The other possibility is that you had enough bacterial activity that it produced acid which curdled the soy proteins. While 3 days in the fridge and 3 hours on the counter are considered safe, there can be one-off cases where you get spoilage going on. This is much more typical for animal milks though (that's how you get buttermilk), I'm not sure how likely it is to happen for soy since I have never observed firsthand how it ferments.

You should be able to make the distinction. If you have off-smells, sour or acrid taste, or other signs of fermentation, this is likely bacterial activity. If the whole thing is bland and firm-ish and reminds you of tofu, it is likely a chemical curdling.

  • Is it safe to consume after cooking? I don't remember if it was soaked three days before or four. For the first day soaking it remained outside.
    – Arrowroot
    Dec 5, 2020 at 14:06

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