Unhappy Hydrometer

[SeanD]

When I'm outside boiling, it is not out of the ordinary for the thermometer to hit my target temp, but my hydrometer says not yet. In the past I have figured it was because of some mixing when I draw off to test - that there must be some trapped low density sweet in the pipe or that some sneaks into the draw off area because my dividers are tacked, not fully welded. Then I'll do another test and suddenly I'm 3 or more points heavy! I've just lived with it for the reasons mentioned. It doesn't happen all the time and it's with different hydrometers.

Well, it just happened again in a batch! It was the last three or so gallons of sweet pulled of the front pan for the season and it was in one big pan with no new sap coming in. There was no mixing and there was nothing in the draw off to thin it out. I hit my temp, tested and it sank very low. It was so low I didn't read it - way past the red line.

So, knowing the hydrometer doesn't lie, I kept going. The thermometer and my eyes told me I had syrup, but the hydrometer wouldn't do it. Then just like off the evap, it suddenly reads many point heavy. This time it was so heavy though, that it clogged up my filter with sugar crystals.

Any ideas why my hydrometer can be so tempermental sometimes?

Sean

[jnmartin]

Sean I'm not a maple syrup expert by any stretch but from my home brew and wine making, I do have quite a history with hydrometers. I can't think of any reason the readings wouldn't be consistent besides sampling and testing method. What's mildly important in wine and beer is magnified in syrup making from what I've observed in just a short maple history. Of course temperature variance can add error, but what I have to watch very carefully is that I don't let the hydro be touching and sticking to the side of the test cup. Also important is having it level and not letting the hydro sink deeper that what the final settling depth will be because of having syrup up the stem on the hydro. As you already know syrup is heavy, sticky, and thick enough to add false weight to the hydro if it is released and allow to bob up and down. For me I have to be much much more careful and consistent with taking syrup density.

Hydrometers can be in error but unless the paper scale inside the stem is loose enough to easily move it will be consistently off in the same direction. If its happening with multiple hydros, the common element in the error is very likely the sampler and technique.

One other thought, if the sampled syrup is frothy and has air entrained in the cup or air bubbles sticking to the sides of the hydro it will cause error

[buxtonboiler]

Hydrometers can also be thrown off by temp. If you notice, they are actually calibrated (for some unknown reason) to be read at 211 degrees, not 219 that most of us actually do. I can only assume that they think the syrup will cool that much from the time we draw it off, to when we actually read it. I have had syrup that I drew off at 220 and the hydrometer sunk like a rock, but slowly came back up as the syrup cooled.

[gmcooper]

SeanD. My thought is part of your issue is with your dividers being tacked and not sealed which would allow lighter sap to mix with syrup in the pans. That can cause fluctuations in flow and cause batching as well as possibly making syrup in the center sections vs the drawoff side. If your firing is not consitant that will add to the problems as well.

Hydrometers are calibrated to read at 211 for hot syrup. If you use a proper test cup with your hydrometer by the time you have filled the cup, the hydrometer has settled as far as movement your syrup will be very close to 211. Remember the syrup in the drawoff valve and the box on the syrup pan is not boiling as there is not heat under it. You may need to watch that the hydrometer does not have a buildup of syrup and sugar stuck to it which will make it heavier. If the hydrometer paper scale gets moved it will be off but it will be off the same everytime. Thermometers are not all created equal and some are just not reliable at all. Also if your thermometer is not in the syrup but up in the foam it will read incorrectly. Many of the digital thermometers are not very accurate at all. I have several here under the counter that read water boiling any where from 185 to as high as 234. At the Verona, NY show this winter the guys from Marcland admitted even the thermometers they sell for candy can be off right from the manufacturer.

[PerryW]

This happens quite frequently for me, especially on my first take-off after reversing the flow.

WHat I think is happening is you are developing syrup in the middle of the syrup pan instead of near the drawoff. I can usually spot this happening by the look of the bubbles and I know to start my draw-off early and let some below-density syrup go through the filter. During the draw-off, it the hydrometer starts floating too high (more then 2 points brix), I shut the drawoff valve, grab the dipper and add a pint or two of sap to the pan (near the drawoff) and restert the drawoff. If the hydrometer is still to high, I repeat the process until I get the density back down to syrup and I can resume the drawoff.