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.

The oxygen conundrum bottles versus cans

Cans keep out oxygen, so they say. Bottle tops don't do quite such a good job, so we are told. It's all to do with the seal that can be achieved. Oxygen can sneak through the tiny molecular gap that might be present between glass and the plastic seal on a cap. Metal to metal is a far tighter closure, apparently.

That is all well and good, but is it possible to get beer into the can reliably without oxygen pick-up? As it happens, Stonch has already cast doubt on that. I can't really be sure, except for the fact that the canning lines I have seen seem to not have all that a reliable way of purging with CO2 and there is certainly no pre-evacuation of the can.

However, our bottling line at Hardknott is the double pre-evac counter pressure filling type machine. What this means is that a contraption attaches to the bottle neck sealing hermetically from the atmosphere. Most of the air¹ is pumped out. The bottle is then filled with CO2 at a pressure of 1 atmosphere gauge pressure², i.e. 2 atmospheres absolute. This process is then repeated again, hence the word "double" in the name.

Only then is the beer allowed to flow into the bottle, under a counter pressure of more CO2 at around 2 bar. When the beer goes into the bottle it is extremely oxygen free. When the pressure is released the beer fobs a little, and we set the rate of bottling to get the right fobbing, along with a little squirt of sterile water to help it foam. This fob is all beer and CO2 with only a tiny area exposed to the air.

The canning lines I have seen try to puff out the air with a little tube that goes to the bottom of the can. The beer is filled from the bottom of the can to try and push the CO2/air mixture of unknown purity out of the can. Any fob will have quite a significant area in contact with the air.

In my view to can reliably with low levels of oxygen it would be necessary to do the process in a blanket of CO2, rather than the open systems I've seen.

Cans might keep out oxygen, but I'm fairly sure it is a lot harder to stop it being in there in the first place. The filling process is certainly not as hermetic as with our bottling line.

Because it is difficult to explain in words I did a little animation for our bottling line.




Top from Hardknott Brewery on Vimeo.

Incidentally, I hadn't really thought about the problems of canning compared to bottling until Jon from Stringers pointed it out to me the other day. All the result of a chat over a beer. Isn't beer good.

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¹Our vacuum pump gets down to about 0.1 atmosphere absolute pressure.

²Gauge pressure is the pressure relative to the atmosphere.