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Garrett_McT

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HBT Community,

I have experienced a weird anomaly while monitoring the temperature of my lager fermentation. White Labs German Lager Yeast WLP830. I have been monitoring the wort/fermenting beer temperature periodically, while also continuously monitoring the ambient fridge temperature through the use of a Govee thermometer. After my diacetyl rest I reached a gravity of 1.016, whereas my final target gravity is 1.015. I assumed that I reached my final gravity and pushed it into my slow decline for the cold crash. I took a couple gravity readings while I have been monitoring the cold crash temperature and both came back at 1.019. I was wondering if this was possibly an anomaly due to some aspect that I am over looking. For instance while I am taking gravity readings of my finished boiled wort, I notice if I do not stir the wort vigorously then I get gravity readings below the actual true reading. I am hoping that this is a similar case because I hope that there is not some residual fermentable sugars lying around in my almost completed beer leading to bottle bombs later.

For your information the following data was collected. I have far more data if it is needed.
Target Primary Wort Temp = 52.0 F
T = 0 min, Wort Temp = 53.0F, Ambient Fridge = 39.92F, SG = 1.065
T = 96 hr 30 min, Wort Temp = 51.8 F, Ambient Fridge = 47.84 F, SG = 1.046
T = 145 hr 15 min, Wort Temp = 52.4 F, Ambient Fridge = 48.2 F, SG = 1.022
T = 159 hr 45 min, NOTE: Start of Diacetyl Rest, Target Diacetyl Rest Temp = 60 F
T = 159 hr 45 min, Wort Temp = 52.5 F, Ambient Fridge = 48.38 F, SG = 1.020
T = 213 hr 15 min, Wort Temp = 74.4 F, Ambient Fridge = 75.2 F, SG = 1.016
T = 237 hr 0 min, NOTE: Start of Cold Cash, Target Daily Decline = 3.7 F
T = 268 hr 15 min, Wort Temp = 50.9 F, Ambient Fridge = 48.02 F, SG = 1.019
T = 329 hr 30 min, Wort Temp = 49.6 F, Ambient Fridge = 45.5 F, SG = 1.019

I have approximately 2 days left in my cold crash to reach 38 degrees. Then I plan on bottle conditioning at Primary Fermentation temperature for just short of 4 weeks, and cold storing for 4 weeks. I used a refractometer for all of my gravity readings, and the refractometer has given me consistently true results as compared to my hydrometer.

I feel as though since the wort temperature had dropped at T = 213 hr 15 min to below the ambient fridge temperature that this was a true sign that fermentation has ended, due to the fact that yeast fermentation is considered an exothermic reaction. Especially because, although lager yeast is not top fermenting, there was a sufficient amount of yeast which fell from the top layer at this same time.

But what I could have easily have overlooked is the fact that the temperature change as the fridge warmed during the diacetyl rest changed quicker than the fermenting wort temperature resulting in the Wort Temp<Ambient Fridge, along with the fact that since the diacetyl temp went way higher than I had wanted, so much that it was outside the range of the specified temperature for the yeast culture, which caused the yeast to go dormant and the result of the yeast at the top falling to the bottom.

Thoughts, expertise, experience and opinions are all welcomed! Thank you for your time and sharing of your enlightened knowledge,
Garret_McT
 

dmtaylor

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Refractometers are very difficult to calibrate and read properly at different temperatures, especially when alcohol is present. The best way to know for sure what the real SG is right now is to use a hydrometer, not a refractometer.
 

Sammy86

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First, RDWHAHB.

Next, how are you taking your readings? If you are using a refractometer with alcohol present you are not going to get accurate readings.

I would get a hydrometer, check the gravity and see where you are at.

Good luck!

:bigmug:
 
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Garrett_McT

Garrett_McT

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First, RDWHAHB.

Next, how are you taking your readings? If you are using a refractometer with alcohol present you are not going to get accurate readings.

I would get a hydrometer, check the gravity and see where you are at.

Good luck!

:bigmug:
@dmtaylor thank you for your feedback, I will pay more attention to periodically checking the accuracy of my refractometer as compared to side by side periodic hydrometer readings.

I believe that heat does not effect the refraction of light through a liquid, however a change in the liquids make up, like alcohol I believe does.

@Sammy86 I directly read the brix increments and take two to three samples and coinciding refractometer readings whenever I take a gravity reading. Then I input the reading into BeerSmiths refractometer adjustment calculator for fermenting wort.

In general, I have fairly good accuracy with using my refractometer with repeated checks against hydrometer readings.

I am hoping this is just some unknown anomaly, and I will know soon. Tuesday should be bottling day and I will take a hydrometer reading and refractometer reading to check.
 

dmtaylor

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Indeed, alcohol messes up the reading and requires an adjustment calculator. I have no idea the accuracy of BeerSmith's conversion calculator, but I definitely trust BrewersFriend.com. Take all measurements in Brix, and learn the Wort Correction Factor for your own refractometer, using the following calculator. It ain't rocket science, but you can use a refractometer for final gravity if you do it right.

https://www.brewersfriend.com/refractometer-calculator/
 
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Garrett_McT

Garrett_McT

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Well see that’s the thing. I used the corrected results of the refractometer and the results are above. I’m not sure why the gravity would read 1.016 and then consistently read 1.019 the following two readings.
 
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Garrett_McT

Garrett_McT

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Indeed, alcohol messes up the reading and requires an adjustment calculator. I have no idea the accuracy of BeerSmith's conversion calculator, but I definitely trust BrewersFriend.com. Take all measurements in Brix, and learn the Wort Correction Factor for your own refractometer, using the following calculator. It ain't rocket science, but you can use a refractometer for final gravity if you do it right.

https://www.brewersfriend.com/refractometer-calculator/
Hmmm, I read the steps for the wort correction factor. That’s honestly very interesting. Essentially you are calibrating your instrument. But honestly if the graduations on the refractometer does not read accurately I would just throw it away. Its like saying you have a 12 inch ruler but the graduations are 25% off with a true total length 15 inches. If I am measuring distances with that I would be reading 25% longer. If I had a measuring tape of the same the type of error it would make building a deck treacherous. When you buy an instrument you inherently trust that it reads true.

now knowing this calibration technique I am curious to see if my refractometer is reading accurately. This method is a good approximation, but hopefully mine reads true.
 

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I would think that temperature would affect the refraction of light. You will change the density/viscosity of the liquid as the temperature changes ( and that's why you have to adjust your hydrometer reading back to it's calibration temperature).
Just as replacing the sugar with alcohol changes the viscosity / density of the liquid which is why you see odd readings on a refractometer unless this change is accounted for.

With an Ispindel you can see these changes related to temperature very clearly as you do a cold crash or D rest boost.
 

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The other thing that can have a pretty big impact is striation. The volume of your sample is going to come to room temperature pretty quickly but don't assume that that gravity of your wort or beer is uniform if there is a temperature gradient or active fermentation happening unless you have a chance to stir it all up. You said it yourself - "while I am taking gravity readings of my finished boiled wort, I notice if I do not stir the wort vigorously then I get gravity readings below the actual true reading."
 

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Any chance that you added a spunding valve toward the end of fermentation? With a Tilt, I have noticed a small increase in hydrometer readings when pressure increases in my fermenter.
 

Vale71

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I believe that heat does not effect the refraction of light through a liquid, however a change in the liquids make up, like alcohol I believe does.
In fact it does. Even the refractive index of distilled water changes with temperature, with a complex mixture of solvents and solutes such as beer even more so.

You should try letting your sample warm up to room temperature before taking a reading and see if you get more consistent readings that way.
 

bracconiere

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Garrett_McT

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I am sorry for my ignorance. I guess I should do more listening than talking. I assumed temp doesn't affect refraction because BeerSmith has a refractometer input on almost everything and a tool for a temp adjustment for the hydrometer.

I input my readings, which were converted from brix to SG as above, to the hydrometer temp adjustment. It came out as follows, in the order it is above

1.064
1.045
1.021
1.019
1.018
1.018
1.018
With the most recent reading at T = 410 hr 30 min SG = 1.015

So that is the issue. I need to convert my refractometer readings from brix to SG and then adjust for temp on all my readings. Thank you all
 
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Garrett_McT

Garrett_McT

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Why are you measuring it that often?
The only way I have to take a direct reading of the wort temperature is to open the fermentor and point an infrared thermometer into it. So I figured if I am opening the bucket I might as well check the gravity. The reason as to why I am taking direct wort temp readings, last year when I made my Oktoberfest the wort and yeast cake at the bottom of the fermentor had frozen because it sits right where the refrigerant pumps through. I am monitoring the min/max over top of the refrigerant circulating shelf thing as well as the ambient. Oh! plus I wanted to push into the diacetyl rest right at 1.020 with a target finish gravity of 1.015
 

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That's great and you hit your target gravity. As an aside and just to let you know that all equipment can be spurious I watched a small ferment on my Ispindel and saw the gravity bottom out at 0.998 which was way outside the yeast performance and expectation of 1.024.
I don't normally worry about odd readings just follow the trend so was happy ferment had finished and thought it was a pressure ferment effect on the ispindel.

Transferred and found about 2ml of wort in the bottom of the ispindel hence change of balance and odd reading. Fortunately the Ispindel has been cleaned and resuscitated and ready for next brew.

Hope the lager tastes good in the fullness of time.

Time to invest in a thermowell or an ispindel then you won't need to keep risking your ferment from contamination.
 

bracconiere

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So that is the issue. I need to convert my refractometer readings from brix to SG and then adjust for temp on all my readings. Thank you all

hmm...could just be coincidence?. not sure if the temp correction for a density meter, would be the same as a refractive index?
 
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Garrett_McT

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hmm...could just be coincidence?. not sure if the temp correction for a density meter, would be the same as a refractive index?
Well I am not sure myself either, but it at least made the gravity readings make sense again. So for the near future I am going to be using this as my new procedure until I find out it is wrong.

I am curious to go back and see if my other readings make sense once I make the correction. But yet again I am lazy
 

Vale71

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hmm...could just be coincidence?. not sure if the temp correction for a density meter, would be the same as a refractive index?
It isn't but the difference is probably so small that you'd need readings accurate to the 4th decimal digit to spot the difference. The best (and simplest) option would still be to just let the sample warm up to room temperature.
 

bracconiere

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It isn't but the difference is probably so small that you'd need readings accurate to the 4th decimal digit to spot the difference. The best (and simplest) option would still be to just let the sample warm up to room temperature.

or in this case cool down to 60f from 75f too.... :mug:
 
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Garrett_McT

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I figured I would give an update. I just brewed on Sunday and conducted numerous side by side hydrometer and refractometer readings throughout the mashing process and for the OG. A few people have mentioned it, that the refractometer samples, due to their size, rapidly cools to near room temperature. The hydrometer readings were fairly accurate, like always, but as compared to the refractometer readings: some refrac readings were within a reasonable amount of error in relation to the adjusted hydrometer readings but then again some weren't, with a very large amount of error combined with a large variance.

I guess my new SOP for refractometer readings, as said before from someone else, would be to take a large enough sample in order to accurately measure the temp allowing it to cool or warm to the calibrated temp (of the hydrometer ~60F) and take the reading. That way I will be limiting the sample size, maximizing my finished beer volume, while at the same time taking accurate data.
 

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There is a natural tendency to take refractometer samples from the surface which can be out of whack due to striation and evaporation effects. Unless you had active recirculation going during your mash you might have been measuring sampling inaccuracies vs refractometer reading errors.

One way to eliminate that would be to take your refractometer samples from the hydrometer cylinder.
 
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Garrett_McT

Garrett_McT

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There is a natural tendency to take refractometer samples from the surface which can be out of whack due to striation and evaporation effects. Unless you had active recirculation going during your mash you might have been measuring sampling inaccuracies vs refractometer reading errors.

One way to eliminate that would be to take your refractometer samples from the hydrometer cylinder.
I am trying to avoid taking hydrometer samples in order to limit the amount of beer taken from my batch. I guess I don't quite know what striation is. What is that?

I am not recirculating my mash, I am taking these samples from my fermentor. If I take samples from my mash I have absolutely no problem stirring it vigorously before taking my sample, but I do not want to do the same for my fermenter in order to avoid rousing the yeast.

This is all in an attempt to creating SOP's for each phase of my brewing process. I am striving for very clear repeatable batches and definitively knowing what is happening during each phase so I can fine tune each beer and recipe.

Thank you for your help
 

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Striation is a gradient in a liquid. Happens in all processes that have heating, cooling, fermentation, saccharification, or any other active process going on if there is not active mixing. If you are trying to compare a hydrometer reading to that of a refractometer, my point was to measure the same sample.
 
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Garrett_McT

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In my experiment with my latest mash I did use the same sample. But like I said above, some refractometer readings were close to the coupled hydrometer reading but some were off. And those that were off had large variances and did not seem to have a consistent error to take into account when adjusting future readings. I feel as though that this is due to the rapid heat exchange with the air when I use a syringe to take my refractometer reading.

I should say that I have been using my refractometer for like 6 months now and have been getting readings that make sense amongst the other readings through the timelines of my beer. That is of course up until this lager fermentation, which has me going back to the drawing board about the accuracy of the use of the refractometer.
 

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It's more commonly called stratification (from what I've seen on HBT). The classic new brewer thread "I added all of the extract for a 1.045 beer and measured the OG....it's 1.150".
OR the opposite with all the extract at the bottom and very weak wort on the top so your reading is1.020 and then fermentation stops and then restarts very slowly.
 

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Sometimes you get small air bubbles in the wort sample on your refractometer sampling tab. These can thrown your reading off a bit. When you close the hinged tab, make sure you are not trapping air bubbles in the wort sample.
 
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