Food Tests
When doing a food test practical here’s how you 1 - set the practical up and 2 - know what to
look for. Remembering this will help when both setting up and executing the practical in lessons
and in exams when asked questions regarding food tests. These types of questions always come
up in exams.
Preparing a food sample: break up food using a pestle and mortar.
Transfer to test tube and add a small amount of water.
Stir to dissolve food.
Filter using funnel and lter paper to remove any solids.
1. Starch / carbohydrates
Use iodine orange / brown start colour.
If the iodine turns black then starch is present.
If the iodine stays the same colour then no starch is present.
2. Protein
Use biuret blue start colour.
If the biuret turns purple then protein is present.
If the biuret stays blue then protein is not present.
3. Glucose / sugar
Use 10 drops of Benedict’s.
If the solution turns / changes between green, yellow and brick red then glucose is present.
If the solution stays blue then no sugar is present.
A 75 degree water bath is required for this practical.
4. Fats / lipids
Use Sudan III (Sudan 3).
If the solution has a red stained layer then fats are present.
If there is no layer then no fats are present.
Each test requires di erent solutions. The key things to remember are which solution goes to
which test and which colours each solution change to and are originally. Remembering this will
help you in both lessons and in your GCSEs.
ff fi
When doing a food test practical here’s how you 1 - set the practical up and 2 - know what to
look for. Remembering this will help when both setting up and executing the practical in lessons
and in exams when asked questions regarding food tests. These types of questions always come
up in exams.
Preparing a food sample: break up food using a pestle and mortar.
Transfer to test tube and add a small amount of water.
Stir to dissolve food.
Filter using funnel and lter paper to remove any solids.
1. Starch / carbohydrates
Use iodine orange / brown start colour.
If the iodine turns black then starch is present.
If the iodine stays the same colour then no starch is present.
2. Protein
Use biuret blue start colour.
If the biuret turns purple then protein is present.
If the biuret stays blue then protein is not present.
3. Glucose / sugar
Use 10 drops of Benedict’s.
If the solution turns / changes between green, yellow and brick red then glucose is present.
If the solution stays blue then no sugar is present.
A 75 degree water bath is required for this practical.
4. Fats / lipids
Use Sudan III (Sudan 3).
If the solution has a red stained layer then fats are present.
If there is no layer then no fats are present.
Each test requires di erent solutions. The key things to remember are which solution goes to
which test and which colours each solution change to and are originally. Remembering this will
help you in both lessons and in your GCSEs.
ff fi
