In my school we actually make the ice cream using the instructions in the textbook around this time of year. It really works! (for most the of the students). Sometimes there is salt in the ice cream, and usually there is a bit of mess...
Here are the quantities if you want to try it. In my 2nd grade there are about 160 students.
First, I recommend you make the students into groups of 4. A group of 3 is ok if you need to round off the numbers. 5 is too many, and they get less ice cream each. Make sure to tell them to bring newspapers and an old T-shirt. They need one T-shirt per group.
Next, buy all the ingredients at once, but make sure you have space in a freezer somewhere in the school for all of the ice! It gets used up quite quickly though.
In Korea we can't get liquid vanilla essence, it's usually powdered. One bag (150 g) is enough to last forever. Make sure you taste the powder- I had one batch that had clearly been on the shelf for a while and tasted like chalk.
One bag of sugar (1 kg) will easily do 40 groups. I use one dessert spoon, not a tablespoon as that is too much.
Rock salt is available, but table salt works too. 1 bag (2 kg) will do about 15 groups.
One bag of ice (2.5 kg) will do about 4 groups.
Paper cups- allow 2 per group. In one cup put about 10 chocolate chips before the class. 1 bag (12 oz/340 g Hersheys from HomePlus) should do. You could use strawberry syrup, in which case I recommend you squirt a little into a cup for each group (I'll leave you to figure out why). I also recommend you use one or the other, not both.
Plastic spoons. Buy enough for 1 spoon per student in one class. My classes are about 30. You can wash them and re-use them.
Small plastic bags (2 per group) and large ones (1 per group).
A wad of paper towels (very important!).
Then follow the instructions in the book!
I have a PPT that is basically each step of the process on its own slide with the photo and text from the book.
I start by going through the list of things we need and checking that we have everything. I also tell the students that 120ml is about 2/3rds of a paper cup, and that 1 tablespoon of sugar is too much, so we will use a dessertspoon.
I set out one cup for each group on the front desk and tip about 1/2 teaspoon of vanilla powder in. It's not a lot. Then I give out the cups. Next, I go around with the spoons and the bag of sugar and get the students to hold a spoon over the cup while I pour sugar onto it. Finally I refer to the instructions to tell them to add 120ml of milk and mix well. It doesn't matter if they fill the cup, except the.
Next I hand out the bags. Have spares as I have found some bags didn't seal well. Follow instruction number 2.
Next I go around and dump some ice in each big bag. One bag of ice does about 4 groups. I go around again and dump some salt in. I've never measured it, but a good dose will do it. I tell the students to be careful shaking the ice so as not to damage the bag (the ice cubes have corners which will puncture the bag if it hits the desk too hard.
Put the milk bag into the ice bag. Seal it. Wrap it in newspaper and then in the old t-shirt. Take a note of the time, and tell them to shake for 10 minutes.
10 minutes is a long time. If they have a group of four they can swap every so often. I tried doing a worksheet during this 10 minute period, with the phrasal verbs from the lesson, but this is not a good idea...
You can test if the ice-cream is ready by squeezing it. Usually, some time within the 10 minutes someone will spring a leak. That's what the paper towels are for. If you test the ice cream of the group that had a disaster you can judge how the others are doing.
They have to wipe the top of the inner bag before scraping the ice cream out. At this point you can hand out the cups with the chocolate chips in and more spoons. They can scrape the ice cream into this cup, or into the original mixing cup.
Clean up: I write on the board to give the spoons to me (I have two bags, one for dirty spoons, and one for clean ones), dump the ice and water in the bathroom, and put everything else in the trash.
Watch out, salt water is sticky and corrosive. If it spills, er, when it spills, clean it as best you can.
I use a binder clip to seal the sugar bag and vanilla bag. I put the salt bag, once it's open, into a large zipper bag. It's important to seal this bag as salt is hygroscopic.
