Google Says the Bubbling Cauldron Is Breaking Out. The Smoke in It Is Water

Every October, Google’s trends team publishes a list of what America is searching for before Halloween. This year’s Frightgeist report, posted on 14 October 2026, has a line under “Spooky effects” that is pure chemistry: “How to make a bubbling cauldron” is a breakout search this month, and “where can I buy dry ice,” which spikes every year, is among the top “where can I buy” Halloween searches.

So the country wants a cauldron that boils without a fire, and most of the answers it finds start with a block of solid carbon dioxide. This article explains what that block actually does (the “smoke” is the least witchy part of it), why a cauldron can bubble with no dry ice at all, how much gas a spoonful of powder makes, and how to get the potion to change color from blue to blood red while it fizzes. The witchcraft is a party trick. The handling rules are not, so those are quoted from the people who write them.

What did Google actually report?

A breakout, and a breakout has a specific meaning. Google’s Trends help pages say that for a rising search “If you see ‘Breakout’ instead of a percentage, it means that the search term grew by more than 5000%.” The 2026 Frightgeist post, written by a Google Trends analyst, applies that label to “how to make a bubbling cauldron” for October. The same post says that search interest in “cauldron crock pot” is at an all-time high and that “witches brew punch” is the top trending Halloween drink.

A breakout is a growth rate, not a volume, and the cauldron is a seasonal search, not a new one. Google Ads keyword data, pulled on 21 October 2026, shows “bubbling cauldron” at about 4,400 US searches in October 2025, falling to a few hundred a month over the winter and spring, then climbing again: 880 in July, 1,000 in August and 1,900 in September 2026. “Dry ice cauldron” follows the same curve, from 70 in July to 590 in September, after 2,400 last October. The witches come back every year. What the breakout tells you is how sharply this October’s climb started.

Where does the smoke in a dry-ice cauldron come from?

From the room. Dry ice is solid carbon dioxide, and at normal pressure it never melts: it goes straight from solid to gas. A technical note from MIT’s theater design course gives the temperature as −79°C (−109°F) and then explains the trick in two sentences. The cold carbon dioxide gas is invisible, “but is plenty cold enough to condense water in the air. It is the condensed water vapor which is visible above a block of dry ice as “fog.””

The chemistry demonstration library at James Madison University says the same thing more bluntly: “The “fog” that we see is condensed water vapor though, not carbon dioxide gas.” Carbon dioxide is colorless. The white cloud is a crowd of tiny water droplets, chilled out of the air by the gas rushing up past them.

That explains three things every dry-ice cauldron owner has noticed. First, hot water makes more fog. The MIT note says “The hotter the water, the greater the effect.” Hot water sublimes the dry ice faster and puts extra water vapor in the air above it. Second, the fog is thin on a dry day: the note says that on “a really dry winter day” there is less water in the air to condense. Third, the fog rolls down and spills over the rim. It is colder than the room, and the carbon dioxide underneath it is heavier than air anyway; PubChem gives a relative gas density of 1.53 with air as 1.

It also explains why the effect dies. The water gives up its heat to turn the dry ice into gas, so it cools and can freeze around the chunks. The MIT note says a sustained effect needs a heater to keep the water warm, and fresh dry ice added over time. A slow cooker on its warm setting is the obvious heater, which may be why “cauldron crock pot” is at an all-time high. If you use one for the effect, keep it for the effect, and keep the punch in a different pot.

Why does a fizz cauldron bubble without dry ice?

Because an acid meets a bicarbonate in water, and one of the products is carbon dioxide gas. It is the reaction inside every bath bomb and every effervescent tablet. The two powders sit side by side quite happily while dry. Add water and they dissolve, the acid hands protons to the bicarbonate, and the bicarbonate breaks down into water and carbon dioxide. For citric acid and potassium bicarbonate the balanced equation is:

Citric acid has three acidic protons, so one molecule of it uses up three of bicarbonate and releases three of carbon dioxide. What is left in the cauldron is a solution of potassium citrate. Kitchen baking soda (sodium bicarbonate) does exactly the same job with a different leftover, sodium citrate. The fizz is fastest in warm water and when both powders dissolve together, which is why bath-bomb makers keep them bone dry until the last moment.

What the fizz does not do is get cold. The reaction absorbs a little heat, enough to notice with a thermometer, nowhere near the −109°F that pulls fog out of the air. The gas it makes is invisible, so a fizz cauldron is all boil and no smoke. For bubbling and foam it is easy to make and repeat. For fog it is the wrong tool, and no amount of extra powder changes that.

How much gas does a spoonful of powder make?

More than it looks, and much less than a block of dry ice. All the figures below are our arithmetic from the balanced equation, PubChem molar masses (citric acid monohydrate 210.14 g/mol, potassium bicarbonate 100.12, carbon dioxide 44.01) and the ideal-gas volume at 20°C and sea-level pressure, about 24.1 liters per mole.

Read the last row twice. One pound of dry ice is about 248 liters of carbon dioxide waiting to happen. Matching that with fizz takes nearly four pounds of powder, and you still would not get the fog, because the fog comes from the cold, not from the gas. The fizz is the right tool for a slow, steady boil: a puck dropped every few minutes keeps the surface moving all evening on a few hundred grams of powder.

The mass ratio is the one number worth remembering. By weight, use about 1.43 parts potassium bicarbonate to 1 part citric acid monohydrate. If you use anhydrous citric acid, which has no crystal water, it is about 1.56 to 1, and 10 g of it gives about 3.8 liters. If you use baking soda instead of potassium bicarbonate, it is about 1.2 parts baking soda to 1 part citric acid monohydrate. A kitchen scale beats spoons, because powders pack differently.

How do you make a cauldron that bubbles and changes color?

Add an acid–base indicator, and the cheapest one in the house is red cabbage. Chopped red cabbage simmered in water gives a purple liquid colored by anthocyanins, the same pigments that color red roses and autumn leaves, as Georgia Tech’s classroom guide explains. A Stanford outreach lab gives the color chart: pink at about pH 1–2, dark red at 3–4, violet at 5–7, blue at 8, blue-green at 9–10. A bicarbonate solution is mildly basic and a citric acid solution is distinctly acidic, so the potion moves across that chart as the reaction runs.

1. Make the potion base. Simmer a few cups of chopped red cabbage in water, let it cool, and strain it. You want a deep violet liquid.
2. Load the cauldron with base. Pour warm tap water into the cauldron, add a generous splash of the cabbage liquid, and stir in potassium bicarbonate until it dissolves. The potion turns blue.
3. Add a little dish soap. A teaspoon is enough. It traps the carbon dioxide in a foam that climbs instead of popping flat.
4. Press the pucks. Mix dry citric acid and potassium bicarbonate at the 1 : 1.43 ratio, mist the mix with water from a spray bottle a few sprays at a time until it holds when squeezed, and pack it into a silicone ice-cube mold. Let them dry overnight. Too much water starts the reaction in the mold.
5. Drop and watch. Each puck fizzes up a head of foam. Drop extra citric acid on its own and, once the acid outruns the bicarbonate, the potion slides from blue through violet to a dark red. Add more bicarbonate and it swings back.

The color change is the part guests remember, and it is real chemistry: the anthocyanin molecules change shape as the pH changes, and each shape absorbs a different color of light. A witch who wants the blood-red ending saves a spoonful of straight citric acid for midnight.

Can you get the fog without the dry ice?

Not from a fizz. Fog needs droplets in the air, and there are three ordinary ways to get them: chill the air until its water condenses (dry ice), shake water into a mist (an ultrasonic mister), or heat a glycol and water fluid and let it condense as it leaves a fog machine. Our guide to DIY fog fluid covers the third. The convincing home cauldron combines two of them: a fog source for the smoke and a fizz for the boil.

If you do use dry ice, the handling rules are short and serious. The University of Pittsburgh’s safety guideline opens with the temperature and the consequence: at −109°F, “skin contact for more than a few seconds with dry ice can lead to severe frostbite.” It says to use loose-fitting insulated gloves and tongs, and that thin nitrile or latex gloves are not appropriate.

A fizz cauldron releases a small amount of carbon dioxide by comparison. On our arithmetic, ten pucks make about 34 liters of gas over an evening, against about 248 liters from a single pound of dry ice, and nothing in it is cold enough to burn skin. It is the version you can set up in the afternoon and leave alone on the porch.

What this means on a specification

For a cauldron, “grade” matters less than form and ratio. The ratio depends on which form of each powder you have, because water bound in the crystal adds weight without adding reactive acid. The table gives the numbers for 10 g of acid, on our arithmetic from PubChem molar masses.

Two practical notes. Potassium bicarbonate dissolves well and leaves potassium citrate behind; baking soda leaves sodium citrate. Either fizzes. And moisture is the enemy of a stored mix: a pre-mixed jar of powder that picks up humidity reacts slowly in the jar and is flat by the party. Store the two powders separately, closed, and mix on the day.

About supply. This article reports Google’s published search trends and third-party safety guidance. It makes no claim about ours: it does not say anything about the supply or price of the citric acid or potassium bicarbonate we list, or where that material is made. Alliance Chemical does not sell dry ice. Prices are on the product pages and change with pack size.

Common questions

How do you make a bubbling cauldron without dry ice?

Use the bath-bomb reaction. Dissolve potassium bicarbonate or baking soda in warm water in the cauldron, add a teaspoon of dish soap, then drop in citric acid or pressed pucks of citric acid and bicarbonate. Carbon dioxide bubbles up as foam. It bubbles, but it does not make fog.

Is the fog from dry ice carbon dioxide?

No. Carbon dioxide is invisible. The white fog is water vapor from the air, condensed into droplets by carbon dioxide gas at about −109°F, according to MIT and James Madison University chemistry sources. Hot water and humid air make more of it.

How much citric acid and bicarbonate do I need?

By weight, about 1.43 parts potassium bicarbonate to 1 part citric acid monohydrate, or about 1.2 parts baking soda. On our arithmetic, 10 g of citric acid monohydrate with 14.3 g of potassium bicarbonate releases about 3.4 liters of carbon dioxide.

Why did my cauldron stop bubbling?

One of the two powders ran out. Once all the acid or all the bicarbonate has reacted, the gas stops. Add more of whichever is missing. Cold water also slows the reaction, so start warm. A pre-mixed powder that took on humidity may have reacted in the jar.

How do I make the cauldron change color?

Add strained red cabbage water. Its anthocyanins read blue in a mildly basic bicarbonate solution and turn violet and then red as citric acid takes over, following the pH chart in a Stanford outreach lab: violet at pH 5–7, dark red at 3–4.

Is a dry ice cauldron dangerous?

It needs care. University of Pittsburgh guidance says skin contact for more than a few seconds can cause severe frostbite, that dry ice must never go in a tightly sealed container, and that the gas can replace oxygen in poorly ventilated areas. Use insulated gloves and tongs.

What we stock

Citric Acid Monohydrate - USP Food Grade

2 and 5 lb packs; 55 lb bags. The acid half of the fizz; 1 part by weight.

Potassium Bicarbonate - FCC USP Grade

2 and 5 lb packs; 50 lb bags. The base half; about 1.43 parts by weight.

Citric Acid Anhydrous - Food Grade

2 and 5 lb packs; 55 lb bags. No crystal water, so about 1.56 parts bicarbonate per part.

Key numbers and sources