Brew control
The cheapest instrument in fermenting, and the one that prevents the most wasted batches.
By Scooter M.·Published September 1, 2026 · Updated September 26, 2026
The short answer
An adhesive liquid-crystal strip stuck to the outside of the jar. It reads the liquid through the glass, costs a couple of dollars, needs no battery and is always visible. A probe only earns its place when it is driving a controller.
A wall thermometer, a weather station and a kitchen probe left on the counter all measure air. Your batch is a gallon of liquid with far more thermal mass than the air around it, sitting on a surface that may be colder or warmer than either.
An adhesive strip is in thermal contact with the glass, and the glass is in contact with the liquid. Craft a Brew describes its Fermometer as changing color "to display the current temperature of the fermenting liquid inside the vessel", and that is exactly the distinction that matters. A less accurate instrument measuring the right thing beats a more accurate one measuring the wrong thing.
| Type | Reads | Published range | Best for |
|---|---|---|---|
| Adhesive LCD strip | The liquid, through the glass | Not published for the Craft a Brew Fermometer; comparable strips sold in bands such as 46-82 F, 57-90 F and 46-93 F | Everyone. Buy this first. |
| Controller probe | Whatever it is taped to | Inkbird ITC-308: -50 to 120 C, ±1 C | Driving a heat mat. |
| Kitchen probe thermometer | A dipped sample | Varies | One-off checks. Not for continuous monitoring. |
| Infrared thermometer | The outside surface | Varies | Nothing here. Surface is not liquid. |
Two honest gaps in that table. Craft a Brew publishes the Fermometer's size — about 0.75 by 4 in — its display units and its compatible surfaces, but neither a temperature range nor an accuracy figure. Comparable strips from other makers are sold in bands such as 46 to 82 F and 57 to 90 F, which are cited here as comparisons and not as this product's specification.
Several jars in the Fermentaholics range ship with a temperature strip in the box alongside the muslin cover and band, which is the tidiest way to acquire one.
A strip on the glass covers everything a batch brewer needs. The controller and its probe are for someone running a heat mat, and are a different purchase for a different problem.
Craft a Brew
A four-inch liquid crystal strip that sticks to the glass and reads the liquid rather than the air, which is the distinction that matters.
#ad Price as of October 18, 2026. How this is funded.
Fermentaholics
A gallon jar that arrives with the muslin cover, the band and a temperature strip already in the box, which is the whole non-culture half of a first batch.
#ad No live price feed yet, so no number is shown rather than a stale one. How this is funded.
Inkbird
A dual-stage thermostat with published relay ratings and a stated plus or minus 1 C accuracy, which is what turns a 104 F heat mat into a jar held at 78 F.
#ad Price as of October 18, 2026. How this is funded.
One case: you are running a heat mat and need something to switch it. Inkbird publishes ±1 C accuracy and 0.1 C display resolution for the ITC-308, which is far more precision than kombucha needs — but the probe is not really there to inform you, it is there to control the mat.
The catch is placement. A probe taped to the outside of a jar is partly reading the room, and how much depends on how well you insulate it. Tape it at liquid level and put a folded cloth over it, or the controller holds the air at 78 F while the liquid sits somewhere else entirely.
The strip recommended throughout this page is covered on its own. The Craft A Brew Fermometer review goes through its published specification, the two figures its maker leaves out, and exactly where on the jar it should go.
Heads up: some links on this page are affiliate links. If you buy through one we may earn a commission at no extra cost to you. It never changes a ranking, and we take no payment for placement. The full version.
Ranked on the published rubric. Every row jumps to that product's full write-up below; the button goes straight to Amazon.
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 | Craft a Brew Fermometer Adhesive Strip Thermometer A four-inch liquid crystal strip that sticks to the glass and reads the liquid rather than the air, which is the distinction that matters. | Reading the jar, not the room | 7.4out of 10 | |
| 2 | Inkbird ITC-308 Dual Stage Temperature Controller A dual-stage thermostat with published relay ratings and a stated plus or minus 1 C accuracy, which is what turns a 104 F heat mat into a jar held at 78 F. | Making a heat mat safe to leave alone | 8.4out of 10 | |
| 3 | Score7.7 Fermentaholics Printed Gallon Kombucha Glass Jar A gallon jar that arrives with the muslin cover, the band and a temperature strip already in the box, which is the whole non-culture half of a first batch. | A plain jar with the cover sorted | 7.7out of 10 | |
| 4 |  VIVOSUN Waterproof Seedling Heat Mat, 10 x 20.75 in Eighteen watts, IP67, MET-certified, and published to reach about 104 F from a 68-77 F ambient — which is more heat than kombucha wants, so it belongs under a controller. | Lifting a cold kitchen into the brewing band | 8.6out of 10 |
#1 · Reading the jar, not the room
A four-inch liquid crystal strip that sticks to the glass and reads the liquid rather than the air, which is the distinction that matters.
Who it is for. Every brewer. This is the cheapest way to stop guessing what temperature the batch is at.
Source: Craft a Brew published Fermometer specification (size, display units, compatible surfaces, operating principle), craftabrew.com/products/fermometer-adhesive-strip-thermometer, fetched 2026-09-01. Comparable-strip ranges from retailer listings, cited as comparisons only.
Skip it if. You want a logged, numeric record. A strip is a glance, not a measurement you can write down with confidence.
#ad Price as of October 18, 2026. How this is funded.
#2 · Making a heat mat safe to leave alone
A dual-stage thermostat with published relay ratings and a stated plus or minus 1 C accuracy, which is what turns a 104 F heat mat into a jar held at 78 F.
Who it is for. Anyone who has bought a heat mat. The mat without the controller is the mistake; this is the other half.
Source: Inkbird published ITC-308 specification (control range, accuracy, resolution, relay capacity, maximum load, alarms), inkbird.com/products/temperature-controller-itc-308, retrieved 2026-09-01
Skip it if. You are not running a heater or a cooler. A controller with nothing to switch is an expensive thermometer.
#ad Price as of October 18, 2026. How this is funded.
#3 · A plain jar with the cover sorted
A gallon jar that arrives with the muslin cover, the band and a temperature strip already in the box, which is the whole non-culture half of a first batch.
Who it is for. A first-time brewer, or anyone who has learned that the fewer parts a fermentation vessel has, the fewer places a batch can go wrong.
Source: Fermentaholics published jar listing contents, fermentaholics.com/product/printed-gallon-kombucha-glass-jar-2-pack/, retrieved 2026-09-01
Skip it if. You want to draw a sample without opening the jar. A plain jar has to be opened every time you taste it.
#ad No live price feed yet, so no number is shown rather than a stale one. How this is funded.
#4 · Lifting a cold kitchen into the brewing band
Eighteen watts, IP67, MET-certified, and published to reach about 104 F from a 68-77 F ambient — which is more heat than kombucha wants, so it belongs under a controller.
Who it is for. Anyone brewing in a room that drops below 70 F, paired with a controller rather than plugged straight into the wall.
Source: VIVOSUN published heat mat specification (dimensions, 18 W, UL and MET certification, IP67, temperature band and stated maximum against ambient), vivosun.com heat mat product page, retrieved 2026-09-01
Skip it if. Your house sits at 75 F already. You do not have a temperature problem, and adding heat without a controller creates one.
#ad Price as of October 18, 2026. How this is funded.
Every specification cited on this page came from one of these documents, retrieved on the date shown against the product it belongs to.
Temperature and pH — the two readings that decide a batch, and the strips, mats, thermometers and controllers that give them to you.
The 75-85 F band, what happens on either side of it, why the jar is not the room, and how to fix a kitchen that sits too cold.
What the published relay ratings, accuracy figures and alarms on a dual-stage controller actually mean for a jar of kombucha.
Why a seedling mat published at 104 F is too hot for kombucha alone, which controller to pair it with, and how to set the two up.
The complete equipment checklist, split into required, useful and skippable — with the sizes and materials that actually matter.
An adhesive strip thermometer reviewed on its published specification, the two figures its maker leaves out, and where to stick it.