Logging Bubble Frequency And Pressure In Your Fermenter

In an attempt to add technology to his brewing process [hpux735] build a sensor rig that monitors bubbles and pressure during fermentation. What does this have to do with brewing great beer? We’re not sure and neither is [hpux735], but he’s got some preliminary readings to spark your imagination.

The bubble sensor itself was inspired by a SparkFun Tutorial where fermenting wine was monitored with a data logger. It uses an optical gate to detect the passage of air. But the goal here was to combine bubble frequency with internal pressure measurements to calculate how much CO2 is being vented. Perhaps it would be possible to get an idea of how close the batch is to completion based on those calculations. A hole was drilled into the fermenter side of an airlock to take these pressure readings.

This actually works quite well during secondary fermentation when the bubble frequency is quite slow. The hardware is able to discern a pressure difference before and after a bubble has passed the lock. Unfortunately the system breaks down during the vigorous bubbling that takes place soon after pitching yeast. See a few bubble-counting clips in the video after the break.


21 thoughts on “Logging Bubble Frequency And Pressure In Your Fermenter

  1. I’d actually be really interested to hear how this was put to use – I do a lot of wine brewing at home and generally it’s a case of “just leave it in the cupboard until it seems right”. If there were a sane way of identifying bottling point it would clear my cupboards more frequently.

  2. kind of neat but it will not make any difference. I have been brewing for 20 years and you can miss the fermentation end by 5 days and not make a difference in the quality of beer,wine,etc…

    what would be useful is a specific gravity logger.

    1. I agree this probably won’t make much practical difference for beer brewing but, for mead and wine, I think this could be useful. I ferment my mead to completion and figuring out where I am on that long fermentation tail can spell the difference between having a final product that remains still for years, becomes petillant or becomes a bottle-bomb. In this respect, measuring pressure is much better than bubble logging alone. However, I agree, a specific gravity logger would be the ideal.

    2. Temp logging would be handy as well, and much easier to implement.

      I can see a gravity logger as being some kind of spg float suspended in the fermenter, and logged. I am just not sure how to actually collect that peice of data.

    3. +1 to that brother

      A device which could continuously monitor specific gravity would be freaking awesome. This is a real annoying task to do manually, and each time you slightly add a chance for infection.

      gravity readings are super annoying when using a hydrometer, and the huge waste of sample extracts. This is less annoying since I got a glass pipette and a refractometer, but it’s still a pain.

      1. A hollow float on a flat spring should bend the spring relative to its buyoancy, which depends on the density of the liquid.

        All you have to do is measure how much the spring is bent with a stress gauge. Best connected in a wheatstone bridge with another identical gauge placed crosswise to eliminate temperature effects.

    4. I’ve been also thinking about somehow logging the brewing process. I think the easiest way might be using some sort of scale to measure the weight — from that you could easily calculate the generated CO2 and specific gravity (of course humidity etc would need to be taken into account too but that shouldn’t be too difficult). The problem is finding a scale with good enough precision and repeatability.

    5. The absolute easiest way to log the process is to put the fermenter on a scale, because the escaping CO2 has a mass.

      Knowing the amount of sugar that went into the batch then tells you what’s happening. One kilogram of ordinary household sugar releases 520 grams of CO2, while glucose releases 250 grams.

      Inverted sugar should behave the same as glucose as far as I know.

      1. While I accept that CO2 discharge reduces the wort’s mass, I can’t imagine accurate readings. The weight differential is still quite small. There’s also a LOT of carbon and nitrogen which gets locked up as yeast cells (which flocculate to the bottom of the fermenter).

        I think you’d have to to a weighing after you’ve transferred to the secondary (and assuming you filtered out the active yeast in the process).

        It seems possible to use the buoyancy of a hydrometer – but your average hydrometer is not up to that kind of abuse (I’d never put one directly in the wort.. I know some people do, but broken glass in a batch turns all that work into a dumper.)

      2. Well, the weight differential is on the order of kilograms even with small batches, and you don’t get kilograms of dead yeast (sans the water).

        Plus, you could always calibrate it to take such things into account. Run one batch with just water and sugar to see how much CO2 actually comes out.

  3. Well done!

    I would love to get that data from my fermentation… I don’t know what I’d do with it, other than pretty graphs… Heck, I might even start brewing again just to get that data!

    Though if that fermentation blows, his dev board might be RIP.

  4. Some planted aquarium enthusiasts add extra CO2 to their tanks for the plants. For that, having a CO2 flow rate as close to constant as possible is desirable.

    Pressurized CO2 is the most controllable option, but not everyone wants to make the investment in equipment, or has a place to get a CO2 cylinder easily filled. So yeast fermenters are often used instead.

    Being able to monitor flow rate on these would be nice. Closing the loop, by using the output rate to heat the mixture and force a particular rate, would be even nicer. I don’t think it’s been done yet, and it’s a project I’ve had in mind for a while. Especially if some way can also be found to force aerobic fermentation, which produces more CO2 and less alcohol, without diluting the CO2 with atmospheric nitrogen.

    Even on a pressurized system, monitoring could be useful to detect the “end of tank dump” that occurs in some systems with single stage regulators, and shut off the solenoid.

    So thumbs up on this one!

  5. Nice project. A friend and i have been considering something similar to this for a while, but never really had time to implement a full mcu based solution. instead, since i have a media server always running (i know $$$), i simply aim the optical sensor of the mouse at the bend where bubbles occur in the bubbler, and then record mouse movements with a python script. easy, no setup at all software solution. The servers excess heat provides a nice incubator for ales in the winter too!

  6. The airlock has a built in pressure sensor. It takes work to move the water in the airlock, all you have to do is figure out how much water weight you’re moving per bubble and convert that into a pressure. Once vigerous fermentation stops the position of the bubble between burst and not burst will give you the pressure inside of the carboy.
    It requires calibration for every airlock design, but you only have to do that once so it’s not a huge hassle.

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