What is a Bubble Logger?

The Bubble-Logger is an Arduino device there monitor your fermentation in regards of Temperature, indirectly and indicative SG calculation, yeast activity though motioning CO2 blops pr. minute (BPM) and can display this information into Ubidots or secondly Brewfather. It can also control a heating mat or other slow-working heating-argent.

The software give an indicative rG (reduction in gravity) estimate based on the use of an  S-airlock and a calibrated sensor is used with a precise amount of water (4-4,5 ml)!


This project measure:

  1. the activity of the yeast as CO2 escape the fermenter by a digital sound detector.
  2. Temperature by ds18b20!
  3. Estimate of “reduction in gravity” (rG) is calculated from complex model taking pressure and temperature data into account.
  4. Optional: One channel Relay to control a heat source. (I used the cold shred or cold utility floor as cooling, and hence, only need a heat source)

The Bubble-logger can (optional) send data till “Ubidots STEM” or till “Brewfather.app” if you use this amazing software. The Bubble-Logger hold it own web-server to serve you data too.



Knowing the yeast activity though CO2 bubble measurements over time including the start of decline, we can better foresee when the SG is close to FG, and better make decision on dry-hopping, temperature changes, etc.!

Project outcome

Hence, the goal is to have a temperature logger/controller, one tiny device to take care of measurement of fermentation rate, e.g. showing Acivity as” CO2-bubbles pr Minute” (BPM) and a same time control the temperature at one setpoint! Secondly, to give an indicative rG/SG estimate. The idea is to get one device instead of having both a temperature controller and fermentation-rate logger at a very low price, e.g. 10$ or EUR! Secondly, the idea is also to remove a lot of soldering (e.g. Ispindel) and to get away from placing anything in the tank (e.g. Ispindel/Tilt). In some sense this is a DIY Plaato.


You write rG/SG?

Determinate SG from CO2 bubbles are not easy taken the need of airtight tanks into account. Hence, the logger post SG if an OG is entered in setup and if OG is not entered it just post an negative value as rG (Reduction in gravity). Hence, by duing so we both allows users there hold airtight tanks and follow the strict rules of 4-4,5ml in airlock the possibility to estimate the SG, but if you dont care about airtight tanks, polynomial, and water in airlock, then the rG is just be a relative “number” indicating the fall in gravity for your equipment.

The key here is not the SG but when the “Sum BPM/L” and BPM starts to flatten, and hence, when we should start to consider make a hydrometer reading.  All users of both Tilt, Ispindel and Plaato in the end have to make a hydrometer reading, hence, the game here is to give the user the data to decide when it is time to do so, besides, giving the user data on when yeast activity is falling in regards of decision for dry hopping, temperature changes, cool crash, etc.!   


  • Airtight – For CO2 to be measured the fermenter needs to be airtight! Hence, FORGET you buckets! You need sealed AIRTHIGHT tanks to do this!
  • Krausen-yeast-particles or wort shooting into the airlock will change the rG/SG, hence:
    • A airtight Blow-off system is needed if you use low headspace,
    • Or, a high headspace of 20-30% together with a low temperature and hence a slow fermentation can also overcome this issue!
  • All calculations is based on precise amounts of wort, hence, keep eye on you amounts in Liters.
  • Only tested on brews size up till 27L.
  • Sound detecting is prone to sound, hence, best placed away from other sound.
  • Sound sensor is prone to moisture, needs a “condom”.