Thermometer Woes - Getting it wrong.

Some of you may be more used to using a thermometer to measure the temperature of a liquid than I am. I never worked in a lab, or a factory where I needed to take temperatures to an accurate degree - not until I was trying to mash my malt at 68C did I need to bother about stuff like this. But it's dead simple isn't it? Just stick it in and then read the scale?

No it isn't. You can easily get it wrong like I did.

For a few weeks I've been puzzled by my readings at boiling point. My thermometer read 105C when the wort was boiling. I alternatively convinced myself that this was because the Young's Brewing Thermometer (about £3.50) was rubbish, and I said so on here. Then I thought it was all about the wort being sugary and therefore boiling at a higher temperature.....

It does, but not as high as 105C with a wort of about 1060 specific gravity.

Then I noticed that when placed well into the boiler, but with the bulb nowhere near the hot element, it was still reading about 104C, IN PURE WATER. Something is wrong here I thought, so I ordered a neat little digital thermometer from ebay and tested that. It worked perfectly, but when I put the Youngs thermometer in the same shallow pan, that was also reading almost dead on 100C.....

What the hell is going on here? So, I started fiddling about with the thermometer at different depths and the thing changes when you do that.

After finding this queer behaviour, it started to dawn on me that I shouldn't be that surprised. If only the bulb is in the hot water, you will get a certain amount of expansion on the fluid inside the glass. If I also submerge another nine or ten inches of the capillary tube in the boiling water, in a boiler say, that too will be expanded and the indicated temperature will rise, even though the real temperature doesn't.

So I began Googling on the subject and discovered that there are different types of glass tube thermometers which are calibrated to be either partially submerged or fully submerged, and that it usually says how far to submerge your thermometer on the side.

I put on my specs and took a look at my Young's thermometer and it says on the side near the top "76 millimetre Immersion".

Did I feel a bit stupid? Yes.

I repeated the boiling test submerging 76 mm of the thermometer in the boiling water and what do you think the read out was? It was 100C.

I've marked the distance 76mm from the lower end of the bulb and my mashing temperatures might be more accurate now so I might get the kind of beer I want. A difference of three or four degrees might make a big difference to the sweetness, or alcohol content of a brew so it is worth knowing this fact.

reference: http://www.amrl.net/amrlsitefinity/default/Resources/newsletter/Spring2011/8.aspx

This is a very interesting post, Tony. It illustrates a point I keep trying to make on here.

Put simply - all scientific instruments are just guessing sticks, at the end of the day. They can give an answer to a poorly defined question.

An experienced user of a guessing stick - thermometer and hydrometer are two under inspection here, will get a useful answer. But all too often the answer it gives only tells you that you asked the wrong question.

One example is the OG reading on a kit brew. You put the stuff in a bucket, put in the water and the hydrometer will tell you with some reliability the OG of the tiny sample you took to measure it.

If you take it from the top, you get a low reading. If you have a tap on the FV and take your tiny samle from the bottom, you get a high reading.

This is because the sugars that increase the gravity of the water have this tendency to sink unless uniformly dispersed.

With temperatures taken using a glass thermometer, you have variables such as being warmer at the bottom of the vessel, if heated from below.

Maybe it cools more at the sides of the vessel than in the middle.

And, as you rightly point out, they are calibrated to an assumed depth of immersion.

Here are some suggestions or observations.

For a kit brewer, your best estimate of your OG is from what you put in. Measuring it is a self defeating attempt to prove what is actually known to be correct.

Measuring FG will be a useful way of confirming the evidence you get from tasting the contents of the sampling jar. If you truly believe otherwise, see above.

Most FG readings will be made using rather gassy and slightly cloudy beer, peering through a plastic vessel, looking at the just slightly the wrong part of the scale and in ignorance of the fact that the bubbles that have formed on the hydrometer itself have lifted up by about half a centimetre.

Good points both of you.

Although I think it's always good to remember that before thermometers, hydrometers, star san and pet there was beer! I'm guilty as anyone of going ott with details but at the end of the day people have been making beer for thousands of years, it's good to be scientific and accurate with things but don't sweat the small stuff too much.

DanST said:

Good points both of you.

Although I think it's always good to remember that before thermometers, hydrometers, star san and pet there was beer! I'm guilty as anyone of going ott with details but at the end of the day people have been making beer for thousands of years, it's good to be scientific and accurate with things but don't sweat the small stuff too much.

Click to expand...

Not being critical or anything but I bet if your were to have a taste of those thousand year old beers by today's standards they'd be considered undrinkable.

Personally, I'm tending towards the opposite view and am 'sweating the small stuff'. I'm begining to treat my brewing in a similar manner to how British Cycling came to dominate recently and how the French described it as 'Sorcery'. They did this by a theory called 'marginal gains'. Basically looking at every tiny variable and trying to improve it a bit. All these tiny improvements add up to a a very big improvements. I'm doing this in an attempt to make the best beer I can with the realtively low tech kit I have

That's why I've been so concerned about temperature monitering. I've also been looking at water treatment and I've just ordered a salifert alkalinaty test.I've also become somewhat OCD about cleaning and sanitation

Interesting comments there Slid and Dan.

I am cautious about the bubbles on the hydrometer and know I am only getting a ballpark figure unless the wort is thoroughly mixed and free of gassy bubbles. Dan's right too - beer wants to happen whatever clever business we try to mess it up with, but if you want to go for special effects like extra body from malto-dextrins at the expense of ABV, you are going to have to keep the temperature on the high side in the mash, and how do you know whether you are at 67C or 70C unless the thermometer works? Mind you, having said all that, my beer was working OK even when the thermometer's misuse by me was making it read at least a couple of degrees high at the critical part of the range.

MyQul said:

I bet if your were to have a taste of those thousand year old beers by today's standards they'd be considered undrinkable.

Click to expand...

I don't know if you saw that series of history re-enactment programmes with Ruth Goodman and the two lads, called Tudor Monastery Farm. In it, Ruth Goodman went through how the Tudors made ale on the farm. She had barley raked out on a wooden floor in an outbuilding, and she watered it, sprouted it and then toasted it a bit in an oven when she thought it was about ready. From memory, I don't think she cracked the grain, but it's been a while, so maybe she did. Her next step was to put this malt in a copper and gradually bring it to the boil, boil it a while, add some bittering herbs (maybe dandylion root, and when cool, she added wild yeast she had collected from a barley field by putting out a bowl of some kind of sweet liquid, maybe wort, maybe honey water - I can't recall exactly. Anyway - she made beer....... When the lads who did all the farm work were presented with mugs of this 'stuff' they drank them up and made a sort of a smile, but I doubt from their expressions they would be asking for another off camera :) . It was ale, not beer, but I doubt it would win any prizes.

Here is a copy of the video with very distorted sound track on Youtube. Watch if you like, but I've covered the gist of it. Ale making starts at about 20:30m and then again at 32.50 if you're interested.

[ame]https://www.youtube.com/watch?v=jLyw6w-UH6U[/ame]

I think some level of souring was would have common, even inevitable in ale from centuries ago as their level of understanding of sanitation and wild yeast contamination would have been far lower than what ours is today. Go back far enough and wild yeast would have been the only yeast available

Yeah that was an extreme example MyQul!

You can take it as far as you like really, I don't doubt that you're approach will turn out some fantastic beer but you can still make something pretty good without getting so in depth.

If you enjoy getting stuck in to the fine details and are into your beer enough to tell the difference then by all means carry on and good luck to you but most people (I include myself in this group) can make a brew they're happy with without being so precise.

Wouldn't knock the British cycle team by any means but I'm still the guy on the rusty mountain bike who only goes out on sunny weekends lol!

DanST said:

Yeah that was an extreme example MyQul!

You can take it as far as you like really, I don't doubt that you're approach will turn out some fantastic beer but you can still make something pretty good without getting so in depth.

If you enjoy getting stuck in to the fine details and are into your beer enough to tell the difference then by all means carry on and good luck to you but most people (I include myself in this group) can make a brew they're happy with without being so precise.

Wouldn't knock the British cycle team by any means but I'm still the guy on the rusty mountain bike who only goes out on sunny weekends lol!

Click to expand...

That's one of the things I love about brewing, the basic process is really pretty simple. Mash some grain, boil the result with some hops and ferment - But for every brewer there's a different method and you can make it as simple or as complicated as you like. I think we've all marvelled at those piccy's you see on forums, of guys, that have basically got a shiney micro brewery in their garage!

DanST said:

Yeah that was an extreme example MyQul!

You can take it as far as you like really, I don't doubt that you're approach will turn out some fantastic beer but you can still make something pretty good without getting so in depth.

If you enjoy getting stuck in to the fine details and are into your beer enough to tell the difference then by all means carry on and good luck to you but most people (I include myself in this group) can make a brew they're happy with without being so precise.

Wouldn't knock the British cycle team by any means but I'm still the guy on the rusty mountain bike who only goes out on sunny weekends lol!

Click to expand...

That cant be much in the uk then again its rusty:hmm:

Picking up on the 'olden days' sub-thread, the thing that I often ponder is how they got the mash temp right without a thermometer ?

My theories include :-

They mixed known quantities of boiling water with cold (from trial and error).

They heated the water to 'too hot to keep your finger in' temperature.

Anyone know ?

Twostage said:

Picking up on the 'olden days' sub-thread, the thing that I often ponder is how they got the mash temp right without a thermometer ?

My theories include :-

They mixed known quantities of boiling water with cold (from trial and error).

They heated the water to 'too hot to keep your finger in' temperature.

Anyone know ?

Click to expand...

I suspect they put the barley in cold water and gradually brought it up to the boil. This would mean that the wort would spend a period of time in the temperature zone where the enzymes beta and alpha amylase could convert the starch to sugars, then as the temperature went up into the 80C range, they got a mash out :) and onwards and upwards to the boil. I expect that the medieval brewers caught on to the fact that a slow fire gradually raising the temperature produced better results than a ferocious one that boiled the wort in a quarter of an hour. People then were as sharp witted as we are, and they noticed stuff as they practised a trade and passed it on to their assistants.

People have been making beer of sorts since Stone Age times.

I did see a Time Team where they made a beer and the temperature for striking the grain was gauged by watching the surface of the water and striking when you could no longer see a reflection on the surface of the water. I had a look at this the next time I brewed and it was about right, mid 70s as a strike temp.

Here's on for you. A couple of days ago I checked that the stc controlling the freezer was reading the same temp as the fridge Stc as I wasn't using the freezer. I did this by bunging the probe from the freezer stc into the fridge, let it settle, then turned it off.

Yesterday I decided to move my Ridleys mild into the freezer to chill it to drinking temps and set the stc to 5.

Didn't move the probe back did I ? 10 litres of mild lollipops anyone ?

MyQul said:

I think some level of souring was would have common, even inevitable in ale from centuries ago as their level of understanding of sanitation and wild yeast contamination would have been far lower than what ours is today. Go back far enough and wild yeast would have been the only yeast available

Click to expand...

I'm sure you're right about the souring, and in fact they only had wild yeast, so i doubt they'd think of it as contamination. It was a sort of magic material to them. They used the same wild yeasts for baking too, and grew them on in the kitchen and brew house - and best of all, everybody drank beer all day long - weak in the day and stronger at night if they could afford it.

Twostage said:

Here's on for you. A couple of days ago I checked that the stc controlling the freezer was reading the same temp as the fridge Stc as I wasn't using the freezer. I did this by bunging the probe from the freezer stc into the fridge, let it settle, then turned it off.

Yesterday I decided to move my Ridleys mild into the freezer to chill it to drinking temps and set the stc to 5.

Didn't move the probe back did I ? 10 litres of mild lollipops anyone ?

Click to expand...

The mild survived it's two day trip to -20c and tastes just fine :-P

Twostage said:

The mild survived it's two day trip to -20c and tastes just fine :-P

Click to expand...

Quite lucky there. My few experiences with bottles of beer left to freeze were not good; flat beer with a horrible insipid taste.

Tony1951 said:

; flat beer with a horrible insipid taste.

Click to expand...

Isn't that what mild normally is like anyway?

Getting back to the subplot of medieval brewing - it's kind of an arrogant assumption that a bunch of modern people with little experience attempting to do something that was a daily job for someone back in the day can produce results anywhere near as good. It's like these re-enactment guys dressing up in fake armour and using fake swords could last more than about 5 seconds on a real medieval battlefield.