If you are a wine, beer, or cider maker, you’ll know the ritual of checking for fermentation. As the yeast does its work of turning sugar into alcohol, carbon dioxide bubbles froth on the surface of your developing brew, and if your fermentation container has an airlock, large bubbles pass through the water within it on a regular basis. Your ears become attuned to the regular “Plop… plop… plop” sound they make, and from their interval you can tell what stage you have reached.
[Chris] automated this listening for fermentation bubbles, placing a microphone next to his airlock and detecting amplitude spikes through two techniques: one using an FFT algorithm and the other a bandpass filter. Both techniques yielded similar graphs for fermentation activity over time.
He has a few ideas for improvement, but notes that his system is vulnerable to external noises. There is also an admission that using light to detect bubbles might be a more practical solution as we have shown you more than once with other projects, but as with so many projects on these pages, it is the joy of the tech as much as the practicality that matters.
maybe instead of an optical system and ultrasonic transducer on each side of the airlock to detect fluid or bubble as its passes by.
Or measure the presuure in the fermenter as it takes so many mm of water pressure to emit a bubble.
Jenny, as you’ve mentioned, there are possibly better ways with less error prone results…
Though this is on the least intrusive side of the scale.
I’d initially gone for the more intrusive side of the scale out of ignorance and used capacitive bubble detection.
I suspect after each bubble, some electrolysis may occur due to the (re-)charge process, even though the electrodes are insulated by the plastic/glass.
No. Through a dielectric you do not have any net charge transfer so no electrolysis can occur. If your arrangement of capacitive electrodes is able to count bubbles, I would consider it just perfect. No disturbance through light or sound is possible.
Bubbles may be exciting but they’re an unreliable method of determining the stage of fermentation.
The specific gravity is the best way to tell what’s going on in your brew.
Place the vat on a scale to get mass. Loss of CO2 causes loss of mass, indicates state of fermentation.
Perhaps a pressure transducer with a very tiny bleed hole on the vent side could give the brewer an idea of vent intensity, as well as frequency of when the events occur. Someone savvy enough could write a few lines of code to set a threshold, and wire it up, and watch their brew on a device.
The action of catalyse in the yeast is a direct measure of it’s metabolic activity and this can be detected because it is an exothermic reaction. This is about 178 watt hours of heat per litre of ethanol produced. For every 1 mol glucose consumed, 2 mol of ethanol and 2 mol of CO2 are produced, therefore if you can account for ambient pressure the volume of your bubbles is proportional to ethanol production, correlating thermal and CO2 output should make your calculations more accurate.
Enjoy your class 1 carcinogen.
And while I remember, you can measure your bubbles with an inverted version of the rocker mechanism used to measure rainfall as in both cases you are measuring a fluid volume trying to move with respect to gravity and only the direction is reversed.
You can simply weigh the fermentation vat and calculate the lost mass of the outgassing CO2.
But you also have to remember that the fermented drink will retain about 0.8 volumes of dissolved CO2 in it.