Instructables
Picture of Easy Litmus Strips
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Have you ever wanted to test if your fruit and vegetables are really organic? Ever wanted to know if you've washed off all the nasty pesticides and fertilisers on that salad? The average human consumes up to two litres of pesticides every year, so litmus paper can be very useful in everyday cooking and of course, scientific experiments. Fortunately, making litmus strips yourself is very easy and cheap, and you can make as many as you want without having to repeat the process. 

You will need:
Distilled Water (tap water works, just not as well)
Red Cabbage
Paper (acid-free, art paper works best)


Step 1: Break and Boil

Picture of Break and Boil
Cut off as many leaves as you want, though you will probably only need about two or three. Then, place these leaves into a pot or deep saucepan. Then you can boil the distilled water, however make sure there is no water already in the kettle because this will contaminate the distilled water. Once the water has boiled, pour it into the pot. Cover the top of the pot with something, preferably a lid of some kind. This will speed up the infusion. Leave the infusion for about 15 minutes, but longer is better.

Step 2: Dip and Dry

Picture of Dip and Dry
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The water should be dark purple-ish by now, if not leave it for a few more minutes. Place a few strips of paper in the post, before removing them with a glove and placing them on a large plate. You don't need to wear a glove, but distilled water is dangerous for your health if swallowed and it may still be hot. The strips shouldn't overlap, but you can dip as many strips as you like. Leave them to dry for an hour or so. 

 
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Theoscillate (author) 12 months ago
True, but very often organic means "no fertilisers or pesticides whatsoever". But if they do contain natural fertilisers or pesticides, you are correct.
kymyst12 months ago
I think you are confusing the words "neutral" and "natural". Neutral means neither acidic nor alkaline, and a neutral substance will not change the colour of litmus ( or in your recipe, the flavanoid colouring matter in red cabbage ). You seem to be saying that only artificial acids or alkalis will affect the pH. Natural fertilisers ( manure, etc ) can also produce high or low pH values, and you would need to use analytical chemistry techniques to tell the difference.
Theoscillate (author) 1 year ago
kymyst: The pH of vegetables and such are affected by artificial pesticides and fertiliser. If they are natural fertilisers, you are right, it will not affect the pH content, so the food is organic by definition. dekyos: Distilled water contains no minerals, so it can absorb these minerals and electrolytes from our body. It is true that you would have to drink a large amount, but I would hate for someone to be injured making litmus paper. If I didn't mention the risk, someone may drink it as normal water, and be injured.
kymyst1 year ago
Could you please explain how testing with litmus paper can tell whether fruit and vegetables are "organic" ? And how do pesticides and fertilizers affect litmus if they are neutral ? Your claims seem rather exaggerated. Litmus paper prepared in this way will indeed detect acids and alkalis, but will not tell you whether they are natural or derived from added chemicals. I would suggest that all fruit and vegetables ought to be washed thoroughly before doing this test to avoid misleading conclusions. Distilled water is only harmful if you drink a large quantity, there is no need to be afraid of a few drops.
dekyos1 year ago
What do you mean, distilled water is bad for your health? Is there something in the red cabbage that becomes toxic when boiled?

I see no materials in your instructable that would be considered hazardous to your health, please explain.