View Full Version : Can fruit pulp affect specific gravity?

11-18-2008, 06:28 PM
When making a melomel, how would suspended fruit pulp affect the measured specific gravity?

I have a prickly pear cactus melomel (http://www.gotmead.com/forum/showthread.php?t=13520) with an expected starting gravity of approximately 1.120 (8 pounds honey, 2.5 gallons target volume), but I measured 1.077.

The cactus tunas were peeled and coarsely strained to remove the seeds. The puree was boiled with water. The honey was added to pasteurize along with yeast nutrient and pectic enzyme. The cooled must was transfered to a carboy with no further fine straining (my mistake?). Cold water was added to bring it up to the target volume.

Thanks for any assistance.

Medsen Fey
11-18-2008, 07:02 PM
My experience with fruit pulp is that it usually causes the hydrometer to float a little higher giving a gravity that is slight higher than the true gravity. Straining out the pulp from your sample and measuring again should provide a clear answer.

Are you certain all the honey is mixed in well?

11-18-2008, 07:24 PM
A substantially lower reading makes no sense at all then. I am relatively certain that the honey was well mixed as it was added to the boiled fruit puree and then stirred quite well as it pasteurized for about 10 minutes at 160 degrees F. The whole mixture was then transferred to the carboy and the cold water was added up to the target volume. The car boy was shaken for a few minutes to aerate and mix prior to the reading being taken.

Unfortunately, I am already nine days into the fermentation so straining the pulp (which has now largely all floated to the top of the must) is probably not a good option. I plan on racking at two weeks due to some comments I read regarding the Lavlin EC-1118 yeast I used. I will check specific gravity then and also get a refractometer reading in order to backfire the original gravity.

It was likely just operator error, but I have used this same hydrometer successfully a number of times for beer brewing and hoped for an answer different than "equipment smarter than operator." ;-)

11-18-2008, 07:43 PM
Hi osluder and let me add my welcome!

Are you sure you added water to MAKE 2.5 gallons or did you add 2.5 gallons of water to your honey? The Mead Calculator (off to your left in the menu) gives an OG of 1.117 if your total volume is 2.5 gallons but gives an OG of 1.090 if you added 2.5 gallons of water to 0.75 gallons (8 lbs) of honey for a total volume of 3.25 gallons. That seems a lot closer to your reading.

Unless your pulp is really, really thick it should only change your reading by a couple of points. Be sure to de-gas your sample thoroughly by swirling it. Any bubbles on your hydometer will throw your reading off. Some people also run it through a paper towel or a coffee filter too. Not the whole batch mind you, just the sample!

Medsen Fey
11-18-2008, 07:47 PM
With the EC-1118, it should go dry even if the gravity was 1.120. After it finishes, you can try a vinometer to see what alcohol reading you get - that may tell you as well.

And I shouldn't forget -

Welcome to the new and improved* GotMead!


* It's not easy being green.
but green can be cool and friendly-like.
--- Kermit the Frog

11-18-2008, 08:11 PM
Thanks for the welcome.

Total volume was 2.5 gallons in a 3 gallon carboy. (I had pre-measured the fill line when sanitizing the carboy to ensure a correct volume.) Basic recipe volumes were:

4 cups fruit puree + 1 gallon water boiled for 30 minutes (so some evaporative loss)
8 pounds local wildflower honey added to fruit mixture
A little over 1 gallon cold water added to achieve target volume

I thought I used my normal (beer brewing) hydrometer procedure of pouring the sample into the test jar, tapping it to knock loose any bubbles from the sides of the jar, dropping in the hydrometer (high gravity, 1.060 - 1.130; I make a lot of big Belgian-style ales), spinning the hydrometer to again dislodge any bubbles and taking the reading.

I must have missed something though, so I will report on the backfired gravity in a few days.

11-18-2008, 09:05 PM
One other question: did you physically weigh the honey or go by a volume measurement? Eight lbs is an odd measure, at least for a normal commercial volume, and would equate to approximately a quarter gallon. Six lbs (half gallon) of honey in 2.5 gallons would give an OG of 1.088 and 5.286 lbs would give your 1.077 reading.

11-18-2008, 10:51 PM
I went by physical weight. I started out with a full 12 pound (1 gallon) jar. I poured off an amount into an empty 4 pound (42 ounce) jar. I then used the balance of 8 pounds.

11-22-2008, 03:20 PM
Racked today at 13 days. Readings were:

refractometer = 19 brix
hydrometer = 1.055 @ 60 F

This backfires (using ProMash) to an original gravity of 1.118 which is right in line with what was expected for 8 pounds of honey in a 2.5 gallon target volume.

Still not sure how I got 1.077 (1.078 temperature corrected) the first time, but I obviously fubar'ed something. The most logical answer is that I did not mix the "top off" water in as well as I thought before taking the sample. It seems every other possible error (e.g., fruit pulp, gas bubbles on hydrometer, etc.) would have resulted in a higher gravity, not a lower one.

11-23-2008, 11:34 AM
Welcome to GotMead?!

Personally, I always do just the juices to the SG that I am aiming for, THEN add the fruit. That way you have a recorded amount for future reference.