advice on pressure sensor for beer fermentation

Hi there, my first post.

I am an avid beer home brewer, recently I've started to monitor my beer temperatures with the 1wire sensor and now I want to add another dimension to the data by adding a pressure sensor. If you are a home brewer or not, there is a gas blow off tube installed to safely remove the co2 gas from the fermenting chamber - because otherwise it would eventually build up and explode. When yeasts eat sugar, they create co2 gas and alcohol and also create heat as the by product of the reaction.

I want to monitor the heartbeat of the fermentation and the frequency of the hops and correlate the data later with the temperature sensor. I am also capturing date-time.

My question is // what kind of sensor would be good to use here, I want something accurate, but I don't think it has to measure too high because like I said before, there is a blow-off tube employed here, it lets gas out while preventing anything coming into the fermentor (this prevents infection).

Currently for the 1wire I have it hooked up to the Arduno UNO, it sends the signal over the USB cable to the Raspberry Pi and there I pick it over with python script over the serial line. I would like to continue to do the same things here.

Prototype it on the Arduino and send the signal over USB cable (same serial connection) and pick it up with Python on the Pi - I am a better programmer with Python than with C, plus I run the entire web server on the Pi and one of my goals is to also graph the data live into the web site for remote monitoring and also for visitors to see.

I plan to share everything via my blog, once I have the project complete with the code and all.

Let me know what would be best to use for the sensor, it would be placed inside the fermentor, above the beer liquid level, in the headroom of the fermentor - or maybe I could place it inside the blow-off tube, not sure which would be better.

Give us information on pressure range and physical form of the connection required.


Freescale has a whole range of pressure sensors.
MPX5010DP is common on ebay, but has a 10kPa range (~1meter of bubbler water).
You might be able to find more sensitive ones (MPXM5004?).
Carefull. Some are absolute. I think you need gauge.

I recall reading someone's experiments with beer fermentation measurements about a year ago. He had placed a pressure sensor in the airlock in order to count bubbles. If I remember correctly, he concluded that the pressure difference was so low that it was difficult to make trustworthy measurements.

As a fellow brewer, I'm actually wondering what you want to measure. Once the airlock begins bubbling, the pressure is going to remain mostly constant, so it won't tell you anything except that fermentation has begun. If you want to measure the fermentation "heartbeat," a bubble counter seems like a better choice.

I am not sure, what's why I am asking questions.

I use a blow-off tube, not a air lock with smaller bubbles, the tube is inserted into a growler filled with water. It takes certain amount of pressure to push the water level down to the bottom of the tube before the air bubbles come out ?

At first it would be more higher reading and then level off and I would see a bubble once in a while and I could count it to see how often it is created. I have a conical fermentor, so I was going to drill a hole and insert a fitting inside, something that can screw in or insert it into the tube when it comes off from the top and have it be inside the fementor, not sure but I am willing to give it a try, why not..

I can't imagine a sensor costing a lot.

the conical was pressure tested up to 5 PSI by the manufacturer before it leaked, so I am thinking 0 ~ 5 psi would be good ?

The pressure is typically going to be due to the depth of the water in the bucket your blowoff tube is in. Figure 1 cm of water depth is about 1 millibar of pressure. Or 30 inches is about 1 psi.... unless the tube clogs.

But is there any merit to monitoring this? I used to be a home brewer. I don't recall anything about the fermenter pressure being a consideration. I wonder if this is just an Arduino in search of a problem. Not that there's anything wrong with that. It's part of the fun.

Previous posters made good points.
The head of water in the airlock (end of tube to surface) is the pressure inside the vessel. So it will stay fairly constant.
Only the amount of gas will vary.
Maybe you could measure that activity someway.

Freescale MPX or MPXV series sensors are pretty damn good. They can measure this pressure range quite well. They are analog devices, so you need a spare analog pin on your Arduino. Make sure to power them off the same 5v that the Arduino is using.

If you are using a 3.3V Arduino, a simple voltage divider can drop the voltage down to an appropriate level. If you do that, use another analog input with an identical voltage divider to measure the 5V rail. The Freescale sensors are ratiometric so if they only get 4.5V input, their output is scaled by the same ratio. You can even run them off 3.3V but I don't know which ones work well or badly at that voltage.

Yes looking for a problem :slight_smile: for fun and to learn, it's is not critical for beer quality overall, I can detect a lot of activity by measuring the temperature.

If you use an "S" shape air lock then you should be able to sense the movement of the individual gas bubbles using a capacitive sensor.

Freescale MPX or MPXV series sensors are pretty damn good. They can measure this pressure range quite well.

Honeywell has a series of pressure sensors that measure ranges below 100 Pa, according to the datasheets - Safety and Productivity Solutions | Honeywell. They're a little expensive, though.

To detect bubbles, it's the pressure difference right before and after the bubble is released that matters. I can't imagine the "static" pressure is important whether it's several feet into a barrel or an inch below the surface.

The pressure inside the brewing vessel will rise slightly when fermentation starts and will remain fairly constant until fermentation stops, because you are constantly releasing the produced CO2 to the atmosphere. I cannot see what useful information a pressure sensor will give you. General atmospheric pressure variations will have a greater effect on the pressure reading than the brewing process.
If you measure the amount of CO2 produced (by counting the bubbles?), that will tell you how fast your fermentation is going, which may be of more use to you.

thanks for the advice, I have been looking into co2 sensors and would have multiple uses for these on various different projects, so I will look into that next...

You might be able to do something with the below BMP180 pressure sensor.