Which food samples contain starch and how to test for it?

December 22, 2025 •

3 min read

Starch is a polymeric carbohydrate produced by most green plants for energy storage and is the most common carbohydrate in human diets. This article explores common food samples that contain starch and provides a simple experiment using iodine to test for its presence.

Quick Summary

An overview of which common food items, like potatoes, bread, and grains, are rich in starch and how to use a simple iodine test to confirm its presence. Detailed experiment instructions are provided, along with a table comparing starchy and non-starchy examples.

Key Points

Positive Iodine Test: A food sample that turns a dark blue or black color when iodine solution is added contains starch.
Common Starchy Foods: Many plant-based foods, including bread, potatoes, rice, pasta, corn, and legumes, contain significant amounts of starch.
Iodine Reaction: The color change occurs when iodine molecules become trapped within the helical structure of the amylose component of starch.
Energy Source: Starch is a complex carbohydrate that plants use to store energy and serves as a major energy source in the human diet.
Refined vs. Whole Starch: Refined starches (like white bread) can cause rapid blood sugar spikes, whereas whole-food starches (like whole grains) release energy more slowly.
Simple Experiment: Anyone can perform the iodine test at home with common materials to identify starchy foods.

Understanding Starch: The Plant's Energy Reserve

Starch is a complex carbohydrate, or polysaccharide, made up of long chains of glucose units that plants create during photosynthesis to store energy. When we consume starchy foods, our bodies break down these chains back into simple sugars (glucose) for fuel. The presence of starch in food is easy to determine through a chemical reaction with an iodine solution.

The Science Behind the Iodine Test

The iodine test for starch is a simple and reliable method based on a chemical reaction. A light orange-brown iodine solution reacts with starch molecules, producing a dark blue or black color. This reaction occurs because the linear component of starch, called amylose, forms a helix structure that traps the iodine molecules. This trapping process creates a new compound with a deep blue color, a clear indicator of starch.

A Simple Experiment: Testing Food Samples for Starch

To conduct your own experiment to find out which food samples contain starch, gather the following materials:

Iodine solution (can be purchased or prepared from iodine and potassium iodide)
Dropper
Small, disposable cups or a plate
Various food samples (suggestions below)
Control sample (e.g., distilled water)

Food Samples to Test:

Starchy Candidates: White potato, bread, pasta, boiled rice, cornmeal, crackers, lentils, oats
Non-Starchy Candidates: Apple, banana, egg white, butter, cooking oil, chicken

Procedure:

Place a small piece of each food sample on a clean plate or in separate cups.
Label each sample clearly.
Add a few drops of iodine solution to each food sample using a dropper.
Observe the color change immediately and after a few minutes.
Record your observations in a table, noting which samples turned blue-black and which did not.

Comparison Table: Starchy vs. Non-Starchy Foods


Food Sample	Iodine Test Result	Starch Presence	Food Type
White Bread	Turns blue-black	Yes	Starchy
Potato (raw)	Turns blue-black	Yes	Starchy
Cooked Rice	Turns blue-black	Yes	Starchy
Apple	Remains brown/yellow	No	Non-Starchy
Egg White	Remains brown/yellow	No	Non-Starchy
Butter	Remains brown/yellow	No	Non-Starchy
Pasta (cooked)	Turns blue-black	Yes	Starchy

Comprehensive Guide to Starch Content in Common Foods

Starch is a staple in many diets, but its concentration varies widely across different foods. Understanding this can help in making informed nutritional choices. Whole grains, legumes, and certain vegetables are excellent sources of energy-sustaining starches that also provide fiber, vitamins, and minerals. For instance, oats, whole wheat pasta, and brown rice contain higher levels of fiber and nutrients compared to their refined counterparts.

Foods with high levels of refined starch, such as white bread, pretzels, and many snack foods, are stripped of their natural fiber and nutrients during processing. While these still contain starch, their rapid digestion can cause blood sugar spikes. In contrast, whole-food starches and resistant starches (like those found in legumes, oats, and cooked-and-cooled potatoes) are digested more slowly, leading to a more gradual release of energy.

For example, a baked potato is a great source of vitamin C, vitamin B6, and potassium, with an 18% starch content by weight. Corn also contains a significant amount of starch (about 18.2%) but is also rich in fiber and other nutrients.

Conclusion

Identifying which food samples contain starch is a straightforward process using the iodine test, a fundamental technique in food science. The presence of starch, a vital plant energy storage molecule, is a key indicator of a food's carbohydrate content. Foods like potatoes, rice, and bread, which show a blue-black reaction with iodine, are rich in starch and serve as primary energy sources. By understanding and performing this simple test, you can gain a deeper appreciation for the chemical makeup of the foods you eat every day.

Outbound Link

For more detailed information on starchy foods and their nutritional value, consult the British Nutrition Foundation's guide: https://www.nutrition.org.uk/nutritional-information/starchy-foods/.

Frequently Asked Questions

The iodine test for starch is a chemical test that uses an iodine solution to detect the presence of starch in a food sample. A positive result is indicated by a color change from the iodine's original orange-brown to a deep blue or black.

The blue-black color is the result of a chemical reaction where iodine molecules become trapped within the helical structure of the amylose polysaccharide chain found in starch. This process forms a colored complex that is visible to the naked eye.

Foods high in starch include cereals, grains (like wheat, rice, and oats), starchy vegetables (such as potatoes, corn, and peas), and legumes (like beans and lentils).

Yes, you can test for starch in both raw and cooked foods. Cooking and cooling can change the structure of starch, but the iodine test will still work effectively to indicate its presence.

Non-starchy foods include most fruits (like apples and berries), leafy greens (like spinach), most meats, eggs, and fats such as butter and oils.

No, starch and sugar are not the same, though both are carbohydrates. Starch is a complex carbohydrate made of many sugar molecules joined together, while simple sugars are smaller, single-unit molecules. The body must break down starch into glucose (a simple sugar) for energy.

Unripe bananas contain a type of resistant starch. As the banana ripens, enzymes convert much of this starch into simple sugars, though some starch may remain.