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I'm getting inconsistent specific gravity readings.

  • 6-25: 1.116 @ 74.3F (after pitching yeast)
  • 6-26: 1.120 @ 71.2F, pH 4.25
  • 7-1: 1.111 @ 70.2F, pH 4.0
  • 7-3: 1.122 @ 70.9F, pH 3.75

I have a spigot and I thought the honey might have settled to the bottom when I poured a sample, but I stirred the bucket and it came out the same (1.122). The fruit has floated to the top. It sank when first put in. There are bubbles coming up in the bucket when I look directly at the surface, and in the hydrometer tube. On 7-1 the airlock stopped bubbling. I added a teaspoon each of calcium carbonate (to increase pH) and Fermax (to feed yeast) and stirred. I believe the inactive airlock was due to a leak around a rubber grommet. I poured a bit of water on all the grommets and the airlock started bubbling again. Why am I getting increasing specific gravity readings?

  • How are you measuring specific gravity? – Frazbro Jul 4 '19 at 6:04
  • Pour a sample in the glass container, put the hydrometer in, spin it around, wait for bubbles to go away, and read the line 1 step below the visible line above the water level. – Chloe Jul 4 '19 at 6:11
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    Great. It might be worth mentioning that you use a hydrometer in your question - many people use refractometers, and these behave differently i the presence of alcohol. That's clearly not your issue here though. – Frazbro Jul 4 '19 at 6:22
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    When did you add the fruit? In addition, it's advisable to never use the airlock as an indication of anything. It is really just a safety mechanism. – Frazbro Jul 4 '19 at 6:22
  • Oops I forgot about refractometers. I don't know how to use those but I saw one in a YouTube video. I added the fruit 6-25 when I first created the batch. It was only orange peels and a handful of raisins that I boiled. I found the rubber grommet that is leaking air. I used a dropper to add water around the grommet and the airlock started moving again. I can't see bubbles coming from the grommet though. – Chloe Jul 4 '19 at 18:17
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Carbon dioxide will throw off your gravity readings. There has to be basically zero CO2 when you take a reading. Otherwise it will tend to increase the reading. This is likely part of the reason why your first reading is low while the others tend to be a bit higher. Stir your sample for several minutes to get as much CO2 out of solution as possible.

Also it may take time for sugars to come out of the fruit that you have added. This would increase the reading as well.

Then with fermentation happening at the same time, there is somewhat of a tug-of-war going on with increases vs. decreases in specific gravity.

For utmost accuracy, it is important to calibrate your hydrometer in fresh cool 60 F water every time you use it. Bumping the hydrometer in any way can affect the readings by a point or two... more than people might think. Mine seems to fluctuate by a point or two every time I calibrate. Even twice in the same day.

Finally, I would highly recommend to just leave your fermentation alone. There is no reason to check gravity so often. Just leave it alone now for a month or two. Frequent measurement is just asking for off-flavors to come in.

Cheers.

| improve this answer | |
  • Wow so CO2 can affect the FG reading? How do people measure FG? Do they wait for fermentation to stop, then wait some more for CO2 to evaporate? Wouldn't CO2 decrease the specific gravity, because it's a gas and less dense, the same way alcohol is less dense than water? – Chloe Jul 4 '19 at 18:23
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    What happens is the CO2 bubbles will stick to the sides of the hydrometer, making it more buoyant and thus increasing the reading, since CO2 is much less dense than water. – dmtaylor Jul 4 '19 at 22:28

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