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Real data, from my kitchen

The Spoilage Index.

Did you know every food has its own "spoilage smell" you can actually measure? My sensor sniffs the gases food gives off as it goes bad. The line going DOWN means more bad-food gases. Once it crosses the red dotted line, the alarm goes off. These are real numbers from my own kitchen experiments. Not from a textbook.

New experiment Experiment #28 · Jun 2–3, 2026

I redid the rice test. This time the box was actually airtight.

Remember last time when my rice test made a big circle and ended right where it started? Well, I had a hunch the leaky box was just following the room as my house cooled at night. So I sealed everything up tight, swapped to the BME688's gas sensor (the MQ135 is still random noise, sorry MQ135), and ran it for 24 whole hours. Truly, the new line is SO much smoother. Hypothesis: supported!

BME688 gas

Flat ~289 kΩ for 18 hours, then dropped ~10 kΩ near the end.

First real downward trend I've ever measured. (Caveat: room was warming at the same time, so I can't say 100% it was the rice.)

Humidity

Climbed 62% to 88.88%. The whole 24 hours. Never went backwards.

My MVP signal. The rice was clearly biologically alive in there.

MQ135

Pure random noise. Again. Bouncing 460 to 1034.

Two runs in a row of garbage. Officially benched.

Temperature

Followed the AC. Warm, cool, warm again.

Important because temperature changes can fake out the gas reading. Next test: keep the room steadier.

Key finding

HUMIDITY is the better early indicator in my setup. The gas only dropped a tiny bit at the very end, but the humidity climbed the entire time. So my next sensor version is going to lean on humidity a LOT more, not just gas.

Unlock the full 4-page report (PDF) Read the backstory in my notebook
The smelly science part

What each food puffs out as it goes bad

I read a bunch of food science papers, and then I checked the actual smells with my sensor. Turns out each kind of food has its own "fingerprint" of gases, kind of like every food has its own bad-breath. Here's what I found:

Food Main spoilage gases When release starts Fresh → spoiled kΩ
Cooked rice & pasta EthanolAcetaldehydeDiacetyl 6–18 hours sealed 39.5 → 6.7 kΩ
Milk & dairy Lactic acid VOCsAcetone 12–24 hours sealed 30.0 → 8.4 kΩ
Bread & baked goods EthanolMold VOCs (1-octen-3-ol) 1–6 hours past visible mold 28.0 → 9.1 kΩ
Strawberries & berries Ethyl acetateEthanol 4–12 hours unwashed 24.8 → 23.5 kΩ (vinegar-washed: stable)
Yogurt & curd AcetoneDiacetyl 24–72 hours past date in fridge 27.0 → 22.8 kΩ (stable)
Bananas (ripening) EthyleneEsters 24–72 hours countertop 26.5 → 7.2 kΩ