The lab
We thought you just poured syrup in and it turned into a slushie. It does not. Put in too little sugar and you get a big lump of ice that the machine cannot even turn. Put in too much and it stays a puddle. So now we measure everything, write it down, and keep it — even the times we got it completely wrong. Especially those, actually.
Check your dateWell — it is. But that is not its main job. Sugar is what stops the drink freezing solid. Plain water turns into a rock at 32°F. Stir enough sugar into it and it will not freeze until it gets colder than that, so instead of a rock you get a slush.
Which means the “healthy” version of a slushie with the sugar taken out is not a healthy slushie. It is an ice cube. We know because we made one.
Slide it and see what our machine would do. The number is called Brix, which is just a fancy word for how much sugar is in there. 15 means 15 out of every 100 bits of the drink are sugar.
Smooth slush. This is what we aim for.
The machine turns easily, the drink pours, and it holds its texture for the whole party.
The book that came with our machine says use between 13 and 17, and that 15 is best. We check every batch before it goes in the van with a little glass thing you hold up to the light called a refractometer. One drop on it, look through, and it tells you the number.
This is the actual maths we do before every party. Change the numbers and watch what happens.
Be careful with the third box. That is the one we have never actually measured. Different syrups are different, and the only way to know ours is to test it — which is the very first thing on our list. The number sitting in there is a guess that makes our normal mix come out about right. When we measure it properly we will come back and fix it.
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People ask us this more than anything else. A lot of rental companies go vague on it, because saying “yes, one is plenty” means they sell you one thing instead of two. Here is our answer with the maths showing, so you can check it yourself.
Our machine has two tanks and each one holds about three gallons. A gallon is 128 ounces and a cup is 12, so one full tank is about 32 cups. We say 30, because some of it always sticks to the sides and never comes out.
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Where these numbers come from. We assume about one cup per person in the first hour and roughly half a cup each hour after that, because the first round is everyone at once and then it settles down. That is from counting at our own parties, not from a textbook, and it is the number most likely to be wrong. We are still counting.
This is the part that surprises people, and it is the reason we test before we sell anything. How sweet something tastes and how much it stops water freezing are two completely different properties. They only travel together in ordinary sugar because that is what everyone is used to.
Tap Freezing power. Then tap Sweetness. The order jumps around completely, and that is the whole point — how sweet something tastes has almost nothing to do with how much it stops things freezing. Sugar is 100 in both columns, and everything else is compared to it.
| Table sugar | 100 | 100 |
| Glucose | 190 | 70 |
| Fructose (in agave) | 190 | 170 |
| Allulose | 190 | 70 |
| Honey | 146 | 94 |
| Salt | 585 | 0 |
| Sucralose | ~0 | 60,000 |
Look at the two weird ones. Salt is not sweet at all, and it is nearly six times better than sugar at stopping things freezing — that is why people put salt on icy roads. And sucralose, the sweetener in diet drinks, is hundreds of times sweeter than sugar but does basically nothing to the freezing.
So a slushie sweetened only with sucralose would taste sweet and then freeze into a solid brick. We have not tried it yet. We think we know exactly what will happen, and we are going to film it happening.
Lots of parents would rather their kid did not drink Red 40 or Blue 1. Fair enough. You can get colour out of actual plants instead — it is just harder, and some plants are much better at it than others. Here is what we have found out so far.
Hibiscus flowers, black carrots and purple sweet potatoes keep their colour even in a really sour drink. Slushies are sour, so these are the ones that work.
It looks amazing in the jug. Then it fades in the sun and goes a sad brownish colour about an hour into the party. We would rather tell you that than find out at yours.
Plant colours last about twice as long cold as they do warm. Good news: a frozen tank is cold. Bad news: a cup sitting on a sunny table is not.
Here is a thing we did not know. Blue raspberry is not a fruit. Somebody made it up. There is no blue raspberry growing anywhere, so there is nothing blue to squeeze.
The only real answer we have found is a flower called butterfly pea. You soak it and the water goes deep blue — and then if you add lemon it turns pink and purple right in the cup, while you are holding it. We are testing it. If it works it is going to be the best thing at the party.
This is the one we have not made yet. Fresh Press is real limes and agave instead of syrup out of a jug, and the whole problem is getting the sugar right — because with fresh stuff you are mixing it yourself instead of following a label.
Here is the maths, so you can watch us work it out.
Tell it how much you need and how sour you want it. It works out how much agave to add so the sugar lands where the machine is happy.
Two of these are guesses and we have marked them. We have not measured our agave or our limes yet. We put a guess inside a calculator once before and it told everybody our best recipe was a block of ice — so this time the guesses are boxes you can see and change.
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Above: what happens in the grown-ups’ tank, after somebody pours their tequila in. The tequila waters it down, so the base has to start sweeter than you want it to end up.
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Below: the exact same mix in the kids’ tank, where nobody adds anything to it.
The two readouts above do not match, and at first we thought the calculator was broken.
It is not. A base built for grown-ups has to be extra sweet, because the tequila is going to water it down by about a fifth. But nobody waters down the kids’ tank. So the same mix that comes out perfect for the grown-ups comes out too sweet for the kids, and too sweet means it never really freezes — it just slumps in the cup.
So Fresh Press needs two recipes, not one. Same limes, same agave, different amount of agave. We did not know that this morning. It came out of doing the sums, which is exactly what the sums are for.
Every number on this page is waiting on one ten-minute job nobody has done yet. Here is the plan, written down before we do it so we cannot quietly change it afterwards.
Step 4 is the interesting one. If the real number and the predicted number do not match, the calculator is wrong and we will say so here rather than quietly fixing it. That is the whole point of writing the plan down first.
Measuring is quick. Making the Fresh Press recipe work is not, because a real-fruit mix has to survive four hours in a tank on a Texas afternoon without separating, and the only way to find that out is to make it and watch it.
That is why the Fresh Press page says you cannot book it yet. We would rather be slow than hand somebody a broken party.
These stay up. If we only showed you the parts that worked, this would not be a lab, it would be an advert.
The mix calculator further up this page used to have the syrup number built in, so you could not see it or change it. We had guessed that number. It was wrong — so the calculator confidently told people that our normal recipe, the one we have made dozens of times and which works fine, would come out as a solid block of ice.
It sat there like that for a week. Now the number is a box you can see and change, with a note saying we have not measured ours yet. The lesson: a guess hidden inside a machine still looks like a fact.
We were looking at another kid’s business account to learn from it, and we said one type of their video was their best kind. We were going off a screenshot, not the numbers.
Then we actually counted the views. That kind of video was one of their worst — about 3,900 views, when their best one had over a million. We had it backwards by about three hundred times. The lesson: looking at something is not the same as counting it.
It froze into a lump the machine could not turn. We could hear the motor straining. That is the whole reason there is a freeze test at the top of this page — so nobody else has to learn it the way we did, with the noise.
We write these down before we know the answers. That is the only way it counts — otherwise you just quietly forget the tests that did not go your way.
We will put the answers up either way, even the boring ones and the ones where we were wrong. A test you only tell people about when it works is not a test.
Same machine, same measuring, and a candy on the rim of every cup.
Check your date