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ROCK CANDY ... Not to be confused with 'HARD TACK' used for lolly pops etc. |
DEFINITION
DISCUSSION
ROCK CANDY - CLASSIC
ROCK CANDY - BILL NYE SCIENCE PROJECTS FOR KIDS
ROCK CANDY
TIPS & TRICKS
Rock candy is a very simple hard candy made by allowing a supersaturated sugar syrup to evaporate slowly (sometimes for up to a week), during which time the sugar crystallizes into chunks. The crystals can be formed around any rough surface; strings or small sticks are most commonly used. "Stir Sticks," are wooden sticks covered with rock candy used to sweeten drinks (like iced tea). Small rock-candy crystals can be used as a fancy sweetener for tea, coffee, and other beverages. Food color can be added to create a wide variety of interesting crystals. "Rock and Rye" liqueur has a large chunk of rock candy in the bottom of each bottle. ["Rock and Rye" an American rye whiskey-based liqueur flavored with lemon or orange essence and distinguished by a chunk of rock candy in the bottom of each bottle.]
DEFINITION: ROCK CANDY
Rock candy can be made at home or purchased in candy shops. Our goal here is to make it at home or school.
Making Rock Candy is a fun and educational project for children -- but not for very young children. Like most candy making recipes it involves very hot liquid and precautions should be taken to prevent burns.
Rock candy is an good example of crystal formation... too much sugar is dissolved into water making a "supersaturated" solution. You have to boil the mixture at temperatures over 250°F (remember, boiling water is only 212°F) just to get enough sugar into solution.
Crystal Formation occurs when the sugar can no longer sustain the amount dissolved - this occurs when it cools. Crystals need a site for formation and any rough surface will do: string, wooden sticks, dust, just about anything (including the sides of the container). As the crystal forms, imperfections can be taken up and incorporated into the crystal lattice structure. Food coloring takes advantage of this fact and is used to create colored crystals.
RISK OF THE LATE 20TH CENTURY: Kids today aren't used to waiting a full week for a pay-off. Instantaneous Gratification is severely lacking when undertaking Rock Candy - so consider your audience. Some kids, like myself and my children, find it still a wonder to watch.
See the TIPS & TRICKS section below for evaluations of the Recipes included here.
ROCK CANDY
5 cup Sugar (granulated white sugar) 2 cup WaterPunch holes at the top edge of a thin 8" square pan and lace about 7 strings from one side to the other. Stretch the strings so that they don't touch the bottom of the pan. Place this pan into another pan deep enough to catch any leaking syrup.Dissolve sugar in water and cook without stirring to about hard ball stage (247-252 degrees) over medium heat. Pour syrup into laced pan. It should reach a level about 3/4" above the strings. Cover the surface with a piece of foil. Watch and wait. The syrup sometimes takes a week to crystallize. Lift out the laced pan. Cut the strings and dislodge the rock candy. Rinse quickly in cold water and put on racks in a very low oven to dry.
ROCK CANDY
Solids and liquids and gases, oh my. You can make a sugary snack while you see the three phases of matter. All you have to do is perform this experiment.
MATERIALS:
1. An adult. 2. A pot to boil water in. 3. One cup of water. 4. Two cups of sugar. 5. A wooden spoon for stirring. 6. A glass jar, like an old jelly or peanut butter jar. Make sure it's clean. 7. Some string. 8. A pair of scissors. 9. A pencil. 10. Some plastic wrap.DO NOT FORGET THE FIRST ITEM IN THE MATERIALS LIST -- THE ADULT.
THIS EXPERIMENT REQUIRES A STOVE, WHICH CAN BE VERY VERY HOT AND DANGEROUS.
BELIEVE ME, I KNOW.DIRECTIONS:
1. Get the adult to boil the cup of water. 2. Once it's boiling, add two cups of sugar. 3. Stir with the wooden spoon a bit and continue to boil. 4. While that's happening, cut a piece of string and tie it to the middle of the pencil. Test the length by laying the pencil over the mouth of the jar -- the end of the string should not touch the bottom of the jar. 5. Once the sugar is dissolved in the water, have the adult pour the liquid into the glass jar. 6. Lay the pencil over the mouth of the jar so the string is dangling in the liquid. 7. Wait for the steam to stop rising out of the jar. When it stops, cover the mouth of the jar with plastic wrap. 8. Put the jar in a safe place where it won't be disturbed. 9. In a few days, pull the string out of the jar.You started with a liquid, saw some steam, and, if you followed the experiment, you've ended up with a solid. Sorry, but they're not diamonds -- it's rock candy. Normally you should never taste any science experiment, but this is an exception. Isn't science sweet?ROCK CANDY
5 cup Sugar 2 cup Water Food Coloring Aluminum Tins (disposable) String or Thread Candy Thermometer (must go to at least 325°F) Wooden spoonBuy some disposable aluminum tins - square or loaf seem to work the best. Use a pencil to punch small holes into the rim of the tin and drape as many strings across the pan as possible with any two strings touching. Tie knots in the string outside the rim holes to secure the hanging string. The mixture you're going to be pouring is hot enough that any tape used to secure the strings might come off.In a medium saucepan bring the water to a gentle boil. Add the sugar and stir with a wooden spoon. Continue to boil until all the sugar has completely dissolved. Food coloring (1-2 drops) may be added. Continue to boil until the temperature reaches above 260°F then remove from the heat. Let the solution cool for about 5 minutes then pour into the prepared tins. Cover loosely with aluminum foil or waxed paper (just to keep dust off; do not use clear plastic wrap). Punch holes in the cover to allow evaporated water to escape. Place is a warm, ventilated space - like a window sill. Takes about a week or less for all crystals to form.
ROCK CANDY
DIFFERENT COLORS One or two drops of food coloring can be added to each tin after the solution has been poured. You can make different tin with different color crystals. CANDY STICKS Use wooden coffee stirs or popsicle sticks in one tray. Kids can use these sticks at home to sweeten iced tea. SEED CRYSTALS Drop a few "seed" crystals of sugar into one tin without any strings or sticks. See if crystals form. QUESTIONS: Ask kids if they patterns of the crystals look like anything else they may already know... buildings, rocks, jewelry, art... Have them try to draw a their crystals and discuss with others.
Rock Candy, like any candy recipe, is very unforgiving and can fail. I recommend making it at home first to be sure you've gotten the steps down and can reliably create a working supersaturated sugar syrup. Have some Rock Candy Stirring Sticks already tucked away when the magic day comes to pull the strings out of the solution to ease failure.
Crystallization can occur on surfaces other than your string or stick. If you're string is lacking in crystals, pour out the water and examine the tray.
Kids find it hard not to touch the apparatus. You may want to shield it from their view during the week or limit access to 5 minutes a day.