How to detect starch

Finding admixtures in food

This ar­ti­cle will help you to find out how to dis­tin­guish starch from oth­er pow­ders, and how to de­ter­mine its pres­ence in var­i­ous types of food.

[Deposit Photos]

Some­times we have to be able to de­tect starch: imag­ine that you want to make jel­ly, which won’t thick­en with­out starch, but all you can find are un­marked jars with white pow­der on the shelf. Here it’s vi­tal to be able to de­tect starch if you want to know what’s in the jars. It’s easy: de­tect­ing starch is a home ex­per­i­ment that is used in ev­ery­day life.

Starch is a polysac­cha­ride, a sub­stance which is se­cret­ed by sev­er­al plants. There are dif­fer­ent types of starch, but the one we know best is the starch that comes from pota­toes, which is used in pre­par­ing dish­es and drinks. Starch pow­der is white, taste­less, and looks like flour.

[Deposit Photos]

You can make wall­pa­per paste if you add starch to hot wa­ter and stir it. It is also worth learn­ing how to de­tect starch if you want to tell a qual­i­ty prod­uct from a fake one: for ex­am­ple, fake hon­ey of­ten has a 50% starch con­tent, be­cause starch is so cheap.

Let’s find out how to de­tect starch

There is a sim­ple and in­ter­est­ing ex­per­i­ment, which we were shown at school us­ing pota­toes. To de­tect starch, you will need the fol­low­ing:

  • io­dine so­lu­tion, which can be found in most phar­ma­cies;

  • a small dish;

  • a pipette or cot­ton bud.

Take the white pow­der care­ful­ly (you shouldn’t han­dle an un­known sub­stance with­out gloves – as you don’t know what the pow­der is, it’s bet­ter to fol­low safe­ty rules). Then pour a lit­tle pow­der into the dish and with a pipette (or cot­ton bud) add io­dine. Don’t use a lot of io­dine, one drop will be enough to de­tect the starch. Click here to see oth­er ex­per­i­ments with io­dine you can do at home.

Let’s see how it works: the re­sult doesn’t take long to ap­pear! When we add or­di­nary io­dine to starch, you’ll no­tice that one drop on the pow­der turns blue or even pur­ple. So this chem­i­cal ex­per­i­ment can help us to de­tect low-qual­i­ty hon­ey or cot­tage cheese with a high starch con­tent. Even a child can do this ex­per­i­ment, as there is noth­ing com­pli­cat­ed about it. To make your child take an in­ter­est in chem­istry, you can show them this ex­per­i­ment with half a pota­to, this will help them to ob­serve the chem­i­cal process of de­tect­ing starch.

Granules of wheat starch, stained with iodine, photographed through a light microscope [Wikipedia]

How to tell soda from starch if there is no io­dine in the first-aid kit

These sub­stances are sim­i­lar, and if you have to dis­tin­guish them, this is easy to do. The eas­i­est method is to taste the con­tents (if you’re 100% cer­tain that the jars con­tain soda and starch).But if you don’t want to taste them, as soda tastes un­pleas­ant, you can use acetic acid: when vine­gar is added to soda, it be­gins to bub­ble – you don’t have to wait very long for the ef­fect. You may ask why this process takes place. The an­swer is sim­ple: car­bon diox­ide is re­leased.

An in­ter­est­ing ex­per­i­ment with an io­dine so­lu­tion and starch

You should only do this ex­per­i­ment in a spe­cial lab­o­ra­to­ry, with an ex­pe­ri­enced per­son, as you need to use a spe­cial burn­er to treat the reagent. If you don’t know how to use it, then you should have some­one with you who can help, be­cause if you lack ex­pe­ri­ence you may get burnt – work­ing with a burn­er is dan­ger­ous. Be care­ful, then you should get ev­ery­thing right!

In mak­ing the nec­es­sary con­di­tions for the ex­per­i­ment, you will need

  • a test tube;

  • cold wa­ter;

  • io­dine;

  • a pinch of starch;

  • gloves and coat;

  • sy­ringe.

With the sy­ringe, add wa­ter to the test tube and a drop of io­dine to make a weak so­lu­tion. Then add a pinch of starch. You can im­me­di­ate­ly see that the slight­ly or­ange wa­ter will turn dark blue. This state of the so­lu­tion is ex­plained by the re­ac­tion of starch to io­dine.

Mix the so­lu­tion thor­ough­ly with a stick and heat it for a few sec­onds un­til it boils. The wa­ter will start to turn into a trans­par­ent liq­uid, go­ing back to the ini­tial col­or with­out the ad­di­tion of io­dine and starch. Then low­er the test tube into cold wa­ter and watch: a blue col­or ap­pears in the test tube again, and a sed­i­ment may also form.

Study chem­istry, it’s an in­ter­est­ing sci­ence which can help you make great dis­cov­er­ies!