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The famous Thai salad "Som Tam" uses raw, crushed string beans in small amounts, and I have seen recipes that suggest raw normal green beans as a substitution. How will the subsitution affect the dish?

How safe is the original and the substitution of green beans when it comes to phasin/lectin levels present in the raw vegetable? Googling gets you a lot of conflicting and anecdotal evidence...

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  • health effects of the commonly used amount of raw string OR (ill-substituted?) green beans in such dishes. Not controversial/esoteric long term health effects, but the kind that could make a sensitive or not-used-to-it person ill. May 6, 2015 at 23:12
  • Related: cooking.stackexchange.com/questions/30392/… a comment there say it's safe to eat an entire serving of green beans raw May 6, 2015 at 23:31
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    All beans contain the toxin, but the common string/green beans are at a level low enough not to worry about. Otherwise western "nanny state" countries would not allow them to be sold raw!
    – TFD
    May 7, 2015 at 0:54
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    @TFD: according to your comment, I'd expect chicken to be sold "cooked only" as well? Seriously?
    – Stephie
    May 7, 2015 at 6:05
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    @KateGregory: health is only off-topic if you ask questions of the "are green or red apples better for your health"-type. This is, IMHO, more a food safety question - like the effects of raw eggs on your health. Could be phrased less differently but there definitively is an effect of lutein.
    – Stephie
    May 7, 2015 at 6:36

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In most countries string beans and green beans are exactly the same thing (see wikipedia's entry for green bean). They are both words used to refer to various unripe cultivars of the common bean Phaseolus vulgaris. The phrase string bean is older and dates back to when beans had a fibrous string down the pod that you could peal off. The first stringless bean was bred by Calvin Keeney in 1894, and hence the newer name for this product was the "green bean" to emphasize the lack of the fibrous string. Both names are still in wide use today, even for cultivars where the string is not present (most cultivars). I am unaware of any credible evidence that suggests that green beans are unsafe when eaten raw. Some toxic compounds are present in green and string beans at very low levels (the same compounds found at much higher concentrations in uncooked dry beans). However, note that these trace amounts of toxic compounds are considered safe and that most foods have similar trace amounts of toxic compounds.

So when going into a grocery store, if you see the word green bean (at least in the US) you can safely substitute it for any recipe calling for string beans.

Edit: As pointed out by rackandboneman, the species Vigna unguiculata can be eaten raw and is the usual bean used in "Som Tam". However, when translated to English Vigna unguiculata is rarely translated to "string bean". The most common english name for this bean is "yard long bean", "long bean" or "cowpea bean" (see the wiki entry for the bean used in "Som Tam"). Similar to green bean, there is no credible evidence that such pods are poisonous when eaten raw, and "green beans/string beans" do make a good substitute for Vigna unguiculata in dishes where you plan to cut the long bean anyways.

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  • See comment above - the ones used in Thai dishes aren't. May 7, 2015 at 15:41
  • @rackandboneman Well that isn't completely true. Many Thai dishes do in fact use Phaseolus vulgaris, but yes several other Thai dishes use Vigna unguiculata. Such a bean is rarely translated to "string bean" in English (at least in the US). I've edited the answer to reflect this fact. May 7, 2015 at 17:22

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