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I live in the UK. At some point, I was taught that cooked rice that has been left for a while can cause illness.

More recently I've become aware that many people make healthy fermented dishes from rice (in fact, these are some of my favourite foods) (and I find this confusing - how is it that fermenting rice is safe but leaving cooked rice to cool and then reheating it is risky?)

I'm a vegan and my favourite mylks (vegan milk alternatives) include mixtures of rice and other ingredients such as almond, hazelnut or coconut. Also, rice milk is useful when preparing things for children or guests as it's very rare to have an allergy or intolerance to rice, while allergies to soya and nuts are relatively common.

I would like to make my own rice/mixed mylk, but I am concerned about food safety. All the recipes for rice milk I have seen involve simply blending cooked rice with water and possibly other ingredients.

I don't know how the rice mylk and mixed rice mylks I buy are produced, but they are sold as non-temperature controlled products with shelf-lives of years or months.

So, if I make rice mylk myself, is it safe? How should it be stored and how long can it be kept?

I mostly use organic brown basmati (long grain) rice. Sometimes I use organic brown sushi (short grain) rice. Sometimes I use rice that is not organic. I don't know if this makes a difference to the microorganisms that might be found on it.

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    I haven't successfully made good rice mylk yet, but I can tell you what doesn't work, or at least what doesn't give you something vaguely similar to store-bought rice mylk: Cooking rice and blending it. The wonderful sweetness of good rice mylk comes from a fermentation process. – Turion Mar 1 '18 at 20:05
  • Hmmm, from the article you link I'd suggest doing the fermentation process at a cool temperature, i.e. in the fridge. – Turion Mar 1 '18 at 20:10
  • @Turion ahh! everything good comes from fermentation :) but I suspect nothing is gong to ferment in the fridge... I will see if I can find a method for making amazake and try to adapt it – Zanna Mar 1 '18 at 20:13
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    Well I found that amazake is made at 60 degrees C! And I found this recipe for making raw rice milk, which sounds like it would work better than blending the cooked rice... the fermented rice dishes I know how to make involve fermenting the raw soaked blended rice with other ingredients like black gram and fenugreek that help fermentation... A commenter mentioned that the soaking water would ferment by itself after an extra 24-48 hours. OP discards soaking water but I don't discard rice soak water (I rinse soaked nuts though) – Zanna Mar 1 '18 at 20:38
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    @Turion I am going to try this for sure! I'm especially excited that she says cooking will cause it to thicken into pudding by itself! :) – Zanna Mar 1 '18 at 20:44
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You seem to be asking two questions. One about safety of fermentation, the other about how to make rice mylk (safely). While I cannot answer the latter I can answer the former.

The difference between fermentation and spoilage is about control.

With spoilage random species of micro organisms (bacteria or fungi) make up the majority of those processing the food. This often leads to them producing toxins or poorly tasting chemicals. Lactic acid produced by the Lactobacillus family being a really common example.

Fermentation is different however, in that you create the conditions in which a desired species of micro organism (or group of them) can thrive and overwhelm any others that produce undesired results. There are many possible relevant conditions, but almost always relevant are:

  • temperature
  • acidity
  • oxygen level
  • nutrients present (e.g. kinds of carbo hydrates and proteins)
  • chemicals that "bind" water (e.g. sugar and lots of salts)

The overwhelming of other micro organisms is actually what makes fermentation suitable as a preservation technique in a lot of foods. In specific cases it can work much better than cooling.

Now about rice specifically: it contains a lot of carbo hydrates. According to Wikipedia:

Cooked, unenriched, white, long-grained rice is composed of 68% water, 28% carbohydrates, 3% protein, and negligible fat (table).

This is almost perfect for any kind of micro organism. Left to itself after cooking it and keeping it around too long this leads to a lot of different kinds growing in there. The species that will end up "winning" usually are those performing chemical warfare: i.e. poisoning the food for the competition. Unfortunately the toxins they use to fight each other tend to be pretty effective at making us, humans and most other animals, sick too.

Well done fermentation avoids this. Some common signs of bad fermentation are:

  • bad smells
  • bad taste
  • lumps and increases in viscosity
  • unexpected changes in color

So whatever you end up doing: try to know the intended result before consuming it. If it does not match that you're at risk if consuming it. If it does match your expectations your risk is significantly lower, but still not zero.

Additionally try to make sure the tools you use are really clean, preferably as close to sterile as you can get them. The food industry commonly uses 70% ethanol alcohol for this purpose: it kills almost everything. Be careful not to use a concentration stronger than that, it triggers a defense in some bacteria that allows them to survive it ("gram negative" if I recall correctly). Chlorine is even more effective, but also more dangerous to accidentally ingest.

  • Right. I interpreted your question to mean that you thought storing cooked rice could be unsafe and thus you didn't understand why fermented it could be safe anyway. I'm still leaving the answer because it might explain, to other people, why fermenting is safe while leaving to spoil isn't. – Giel Mar 16 '18 at 12:47
  • Yes. Your interpretation is pretty much right. Your answer is very useful to me and others. My question is unclear. But I am not sure how to fix it :) I think I should edit my question to match your answer – Zanna Mar 16 '18 at 13:01
  • Splitting to two questions, like you mentioned before, also seems like a valid option – Giel Mar 16 '18 at 13:12
  • I have slightly edited this question and asked a new question. Thanks for helping me to define this question more sharply – Zanna Mar 16 '18 at 13:50

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