Hydrometer reading differently in cup vs pot

[Gust-o-wind]

Hi, I'm new here. I've been making syrup as a hobby (150 taps) for years but just this year noticed something a little odd. When reheating syrup for canning, I usually check it with a hydrometer to make sure it meets the minimum density before it goes into the jars. Occasionally I have a big enough batch that it's deep enough in the pot to put the hydrometer directly into the pot instead of transferring some syrup to the hydrometer cup for testing. This time I noticed that the hydrometer was floating differently in the pot vs the cup, even though the temperature of both was the same (within 1° anyway). Any ideas why this is happening? I let the hydrometer sit in each location for several minutes to make sure it had equalized.

I guess I can't upload pictures.

In the hydrometer cup at 62°F it's reading 66.6 Brix and in the pot at 61°F it's reading 67.4 Brix.

[Andy VT]

I will say that I have one hydrometer cup that is just barely bigger than the bulb of the hydrometer and I got a bad reading with it. I have not confirmed but suspect that there was some sort of interaction between the sides of the cup and the sides of the hydrometer making it float higher. Just one idea (the only idea I can think of). And the difference was with the syrup cold, like your situation, which to my brain would exacerbate the situation if my theory holds any syrup.

[Brian]

I have seen the cups be a little dirty at the bottom and that changes the reading.

[TapTapTap]

Did you stir the pot before the test? And did you stir the pot before taking the hydrometer cut sample?
Ken

[johnallin]

I have seen the cups be a little dirty at the bottom and that changes the reading.

For that very reason, I hang my cup upside down over the syrup outlet box on the front pan.
The steam cleans the inside of the cup and keeps it hot at the same time.

[BAP]

Unless you are keeping your hydrometer cup as hot as the syrup you are putting in it, the minute the hot syrup hits the cup it is going to cool down much more than 1 degree and change your reading. Have you tried using an instant read thermometer in the syrup in your cup the same time you use the hydrometer to see if you need to temperature adjust the hydrometer reading?

[Gust-o-wind]

I will say that I have one hydrometer cup that is just barely bigger than the bulb of the hydrometer and I got a bad reading with it. I have not confirmed but suspect that there was some sort of interaction between the sides of the cup and the sides of the hydrometer making it float higher. Just one idea (the only idea I can think of). And the difference was with the syrup cold, like your situation, which to my brain would exacerbate the situation if my theory holds any syrup.

I've had that same thought about narrow cups. But this is a 2" cup which I don't think would affect the hydrometer in that way.

[Gust-o-wind]

I have seen the cups be a little dirty at the bottom and that changes the reading.

This cup was cleaned before use.

[Gust-o-wind]

Did you stir the pot before the test? And did you stir the pot before taking the hydrometer cut sample?
Ken

Yes, I've tried it twice, once at canning temp (180+) and once at room temperature. I stirred the pot both times.

[Gust-o-wind]

Unless you are keeping your hydrometer cup as hot as the syrup you are putting in it, the minute the hot syrup hits the cup it is going to cool down much more than 1 degree and change your reading. Have you tried using an instant read thermometer in the syrup in your cup the same time you use the hydrometer to see if you need to temperature adjust the hydrometer reading?

I do use an instant read thermometer anytime I use a hydrometer (other than drawing off). This particular situation everything was at room temperature so no drastic temperature differences, as confirmed by the thermometer readings.

[buckeye gold]

One more thought. Did you clen the hydrometer between the two test? In cold syrup a lot of syrup sticks to the hydrometer. I keep a thermos of hot sap or water at my finishing or bottling station and the hydrometer gets rinsed each time it's put into syrup. You can build up syrup and resistance. In reality I'm not sure I would have much concern over a difference of 66.6 to 67.4, I'd bottle and never finch. Also the meniscus (liquid curve) around the hydrometer is different in colder syrup then hot syrup, it could be a reading/visual error. I used to have to constantly remind my techs in the wet lab to read graduates and immersed instruments properly.

[TapTapTap]

Yes, I've tried it twice, once at canning temp (180+) and once at room temperature. I stirred the pot both times.

Did you stir the pot before taking the cup samples too? How did you take the cup samples - draw-off or dipping the cup?

[Vtmbz]

A paper that came with my y hydrometer says a 10 degree change in temperature results in a change of brix of .5 points. Are you letting your two samples vary by 10 degrees? Not likely.

I am very careful to rinse off my hydrometer and wipe it dry between samples. There is no need to rush. I keep my test cup hot. I also try not to have it bob up and down so that syrup would stick above the float level and add weight.

[Pdiamond]

John - I am very curious on how you manage to hang your cup upside down above, so the steam keeps it clean. It is an intriguing idea to me and I just can't picture it in my head.

[johnallin]

John - I am very curious on how you manage to hang your cup upside down above, so the steam keeps it clean. It is an intriguing idea to me and I just can't picture it in my head.

Design with ring handle hangs just fine over drawoff box.

[Gust-o-wind]

One more thought. Did you clen the hydrometer between the two test? In cold syrup a lot of syrup sticks to the hydrometer. I keep a thermos of hot sap or water at my finishing or bottling station and the hydrometer gets rinsed each time it's put into syrup. You can build up syrup and resistance. In reality I'm not sure I would have much concern over a difference of 66.6 to 67.4, I'd bottle and never finch. Also the meniscus (liquid curve) around the hydrometer is different in colder syrup then hot syrup, it could be a reading/visual error. I used to have to constantly remind my techs in the wet lab to read graduates and immersed instruments properly.


I did not clean it between the pot and the cup. I moved it back and forth between the two several times to confirm that it was not just a one time fluke. I didn't let syrup stick to the stem of the hydrometer above the test level. Since both samples were the same temperature, I don't think it's a reading error. It's more than a 1/4" difference on the hydrometer between the two readings.

[Gust-o-wind]

Did you stir the pot before taking the cup samples too? How did you take the cup samples - draw-off or dipping the cup?

I used a ladle to fill the cup directly from the pot. Remember this was all at room temperature. No significant difference between the temperature of the syrup in the pot or the cup. I did stir the pot to make sure it was evenly mixed before filling the cup.

[Gust-o-wind]

A paper that came with my y hydrometer says a 10 degree change in temperature results in a change of brix of .5 points. Are you letting your two samples vary by 10 degrees? Not likely.

I am very careful to rinse off my hydrometer and wipe it dry between samples. There is no need to rush. I keep my test cup hot. I also try not to have it bob up and down so that syrup would stick above the float level and add weight.

There was one degree temperature difference between the syrup in the pot and the cup, using the same thermometer for both readings. Nothing was hot during the tests, so no need to keep the cup hot. This occurred in my kitchen before heating for canning, not at the evaporator.

[Gust-o-wind]

Still says "upload failed" when trying to add pictures. Maybe I need 10 posts before I can upload pictures?

[Gust-o-wind]

Post #10. With 10 characters.

[Gust-o-wind]

Still can't seem to add pictures. I'll give it a little time and try again.

[BAP]

Still can't seem to add pictures. I'll give it a little time and try again.
There is no uploading pictures on this site anymore. The owners have not updated the software to allow it. You need upload a link to some other photo hosting site so people can click on a link to go see the pictures.

[buckeye gold]

I have one final comment then I am out of suggestions. Do you have another hydrometer to check it with. If two different hydrometers do the same thing then I can't think of any answer for you other then just accept the difference and bottle it. The difference isn't big enough to do any harm, it's within normal ranges.