Sunday, 5 June 2016

Temperature Control of Fermentation

There is a risk I am entering into a techie phase in this blog. I'd like to extend an apology to anyone who is checking in for some sort of controversial hyperbole of increasingly doubtful declaration of awesomeness. Making really great beer does require some diligent appliance of science, technology and engineering. We're still a very small brewery, but intent on growing and improving along the way. For various reasons, not least of which is the fact that a lot of brewers read this blog, I thought I'd share some details of our current journey.
Our current temperature control panel.
Note replacement controller at the top as the
original units became expensive to replace.

One of the most important parameters in the brewery is fermentation temperature. Sure, mash temperature is also important, as are things like timings of hop drops in the copper etc, but you can manually monitor and correct for them in process. Fermentation happens over a period of several days. You can't be there all the time to turn on the chilling as and when. Some sort of automatic temperature monitoring and control system is just about essential.1

A simple thermostat would do, to a point2.  Unfortunately this form of control is inherently unstable and there will always be an oscillation of the actual controlled process variable4. This is generally being made worse by the presence of relatively large RC and DV lags5. If you are trying to control at 20 degrees centigrade using a regular thermostat your temperature is highly likely to be oscillating anything up to 2 degrees either side of your set point6. Yeast isn't too keen on this sort of environment.


A LOGO!8 PLC and a touch screen HMI

There is a control technology, which is really quite old, so old in fact that it predates my first study of the subject when I was starting my career in the early 80s. It's called three term control and applies proportional, integral and derivative algorithms to the system to keep the process variable, our fermentation temperature, absolutely blob on and a stable as a rock. It's what we currently use on all our fermentations. Our yeast really seems to like it a lot. However, I think there are better ways of doing it still... The panel I've built is looking a little sorry for itself and the controllers I've used are somewhat overpriced now in my view - long story, but it turns out to be expensive to maintain, despite being originally economic to make. Time has come to update the system

Proving the PLC and HMI can talk to each other via ethernet
At BeerX I had some very lengthy chats with the nice people on the Siemens stand. I had already told them that I had used on of there PLCs7 on a keg washing project. I had already identified that this nice little module has got three term controllers built in. The conversation galvanised some action to actually taker advantage of combined wisdom.

So, as a collaboration project I've decided to work with them to get a turnkey system up and running that is appropriate for the micro-brewery sector. The last two days I've been getting it set up on the bench, complete with a rather sexy touch screen HMI8

There will be more posts to follow describing my journey back into the world of control engineering and hopefully provide some of my previous experience, and even a little bit of my degree to develop cost effective and appropriate automation to the small scale brewer9.

Meanwhile, you'll have to excuse me, I have some PLC programming to do.
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I'm looking forward to getting the trending function working
Being able to graph the control system will help tuning.
1I know some brewers get up at stupid o'clock in the middle of the night to deal with this sort of thing. I have too when something has gone wrong with my system, but you really shouldn't have to. I don't think it's a sign of dedication to the cause, I think it is just daft when the technology exists to eliminate the need.

2Thermostats are what we control engineers3 call "on/off control" - there is almost always a thing employed called hysteresis or time lag, without which noise would be amplified and cause contact chatter.

3Actually, I've come to realise that if I drill down into my skill set, my qualifications and  experience, this is actually my true core skill. Luckily brewing can use a lot of knowledge from this particular discipline, and so I intend to apply a lot more over the next couple of years to make our brewery even better.

4There we go, that's proper control engineering techie speak. The process variable is the thing you are trying to measure and control, in our case the temperature of the fermenting wort.

5Wow, WTF? RC = resistance x capacity and DV = distance / velocity. So, your cooler can apply a certain kW of cooling to your tank. The tank has a certain thermal capacity - that's RC. It is a time constant. The circulation in the tank, which has some sort of velocity figure, means that between the cooling cutting in and the cooler wort being seen by the thermometer will create a time delay. There may also be delays in the cooling system itself, between cooling being demanded and the cooling action actually acting on the tank.

6Set point is just the value at which you are trying to maintain your process variable.

7**yawns** - PLC = Programable logic controller. They are highly specialised little computers that are dead easy to program, if you are a control engineer, to control all sorts of stuff. Quite a lot of bigger breweries automate their production with such things.

8More acronyms - HMI = human machine interface. This one seems quite powerful, and actually the most expensive part of the set-up.

9One of the down sides of this blog, and generally being a little bit gregarious, is that many people call me up for advice. I sort of like that really, but it is a drain on my time. Mostly they are brewers who have not long been brewing and have hit a technical challenge they can't fix, or more often than not people thinking of setting up a brewery and looking for advice. My advice has generally been to try to lean on the side of "don't do it, it'll ruin your life forever".

I think there are too many breweries in the UK now. I'll make absolutely on secret of that opinion. So,  more and more I am becoming reluctant to hand out random advice with no return on the time invested. Indeed, there are one or two notable examples of negative experiences in that respect, I'll say no more.

That might seem a little churlish, and quite unfair on some of my very best brewing friends, who have stayed loyal and friendly, even if just behind the scenes. However, I am now looking for some sort of monetisation for any help I give. I believe there is a gap in the micro-brewery sector of the skills of a control engineer who also has significant brewing experience. I'm pleased to say that Siemens also recognise that and we are developing a very positive relationship. Part of the agreement for me getting some support from Siemens is that I can be a resource to help brewers who want to use their equipment to help automate their brewery. I'm happy to do so, and will continue to monitor if this is a diversification I should be looking to generate revenue from.

2 comments:

BryanB said...

Control engineering, now there's a skillset I've not used in a *long* time... But I still got almost all the acronyms straight off. Good article.

Steve Berke said...

I enjoyed reading this work. I'll come back for more

Keep up the good work :) from TheStillery,stuart bar in Florida