Candy propellant is popular in amateur experimental rocketry, mainly due to the availability of the chemicals and ease of use. It is usually prepared by melting potassium nitrate and sugar together, but this is obviously a somewhat dangerous operation. Dry mixing is possible and much safer but produces lower quality propellant.

The ratio of potassium nitrate to sugar may be varied to alter the properties of the propellant, but the following formulation is most commonly employed

The composition produces a relatively large amount of smoke due to its similarity to smoke mix. You can increase the burn rate of this mixture by adding 1% iron oxide III (Fe₂O₃) to the mixture.

1st method : heating the mixture

Mix 65g of potassium nitrate with 35g of sugar (+ 1g ferric oxide) and gently heat the mixture with a bit of water. Unlike smoke composition, the sugar must NOT caramelize. Avoid gas stoves because they heat up too much and could ignite the mixture.
As soon as you get a thick paste, remove from heat and fill your engine tube.
This method isn’t very practical to fill the tubes and the paste requires a quite long drying time.

If you add too much water, you won’t get a completely dry propellant and it won’t burn well.

2nd method : simple powder

Mix 65g of KNO3 with 35g of sugar (and 1% of Fe2O3) once again. But this time, everything is (individually) reduced to a fine powder using a blender and than mixed together. Note that you can directly use powdered sugar.
This time, we obtain a powder that works just as well as the previous technique. In fact, it works even better sometimes =D

3rd method : optimal powder

We are once again using the same formulation (65 KNO₃, 35 sugar and 1 Fe₂O₃). First, take all chemicals and mix them with an equal volume or more of water. The resulting mix should be like sand in a brown liquid. The next step is to heat on the hot plate. Every crystal should dissolve when it approaches 100 Celsius, otherwise it is important to add more water. When everything has dissolved, keep heating and agitating until water partially evaporates and the mix gets pasty. At this time it is important to reduce heat and agitate well since sugar must NOT caramelize at all. Overheating will make the sugar caramelize and further heating will make the mix ignite. In the middle of the drying process, grinding the granulated chemicals with a mortar and a pestle will help to avoid changing into caramel and will make the drying process faster. After grinding, return the powder back on the stove. the temperature should not exceed 110 Celsius. When the powder is dry, remove it from the hot plate and grind it again to get a fine powder. For greater safety, when the mixture gets pasty it can be removed from the hot plate and let to naturally dry. It is important to grind the chemicals once they look solid and then let dry again to ensure there is no more water.

This is an alternative way to create candy propellant. It creates a very powerful powder that can be compared to commercial black powder used in old French musket when it’s well done. This mixture, unlike candy propellant created by melting sugar, isn’t hygroscopic so it can be stored for a long time without any special devices. The risks of ignition in the making process are lower than in the molten sugar process but when ignition occurs it is much more hazardous. This is due to the fact that this method creates fine entangled crystals of sugar and saltpeter wich create higher contact surface between the sugar and salpeter. You can also make a less powerful propellant just by mixing 60% KNO3 with 40% Sugar.

4th method : wet mixing

This method has a faster burn to it, but requires more work.

Simply mix all ingredients together in a saucepan and bring to a boil on an outdoor heating element. Keep the mixture at a boil until all of the water has evaporated. When the mixture is the consistency of peanut butter, remove pot from heat. Spread mixture out onto cookie sheet and let dry in the sun for several hours. Your fuel should now be brittle and hard. Grind up by placing all material in a plastic bag and breaking it up with a hammer.

Warning

The gas that comes from potassium nitrate-based mixture as it is cooking is a mucus membrane irritant. It is recommended that this be done outside

Try to avoid using a naked flame as a heat source since the direct heat of the flame may ignite the mix, causing you all sorts of problems.