Understanding hydrometer readings

[kzufelt]

Okay, so we are making a hopped mead. Only our second batch of mead and our first using a hydrometer.
We put 15 lbs of honey in 25 litres of water, then activated and added Nottingham yeast. We let it ferment a week and then reracked. We added cascade hops, 1/4 oz boiled in 1 cup of water and 1/4 oz unboiled hops, all in a cheesecloth bag.
We let it ferment another week and reracked again.
Here is my question. Our initial hydrometer reading was 1.052, the second was 1.091, and the third was 1.061.
I thought the readings would progress linearly, but these raised, then regressed.
What's up with that?

 

[Yooper]

I thought the readings would progress linearly, but these raised, then regressed.
What's up with that?

Easy. At least one reading is wrong. My guess is it's the first one. Because with that much honey, there is NO way it was only 1.052. The honey must not have been mixed thoroughly enough to get an accurate reading.

 

[GHBWNY]

Well, a brew doesn't lose and re-gain specific gravity on its own during fermentation. If you are you using the plastic tube the hydro came in, are you filling it all the way to the top every time? If you're filling it only part way, as the SG drops the hydrometer could be bottoming out in the tube and giving you a false reading.

 

[kzufelt]

Not filling it all the way to the top, but I certainly make sure the hydrometer is floating freely.

 

[kzufelt]

We mixed the water and honey in a separate container before transferring to the carboy, specifically to ensure the honey was completely dissolved, but I would agree that the chances of me taking a wrong reading are pretty high. Thanks for the reply.

 

[bernardsmith]

kzufelt - welcome. Just like a lawyer does not ask any question in court for which he does not know the answer that will be given you always want to take a reading when you have some good idea of what that reading should be. Bottom line - there should never be any surprises when you are making mead.
So - 15 lbs of honey is about 1.25 gallons (assuming 12 lbs = 1 gallon) .
25 l of water is about 6.5 (slightly more) gallons . Your total volume is then 7.75 gallons . Yes?
That is then about 2.2 lbs of honey per gallon. Yes?
One pound of honey will raise the gravity of 1 gallon of water by 35 points (1.035) so 2.2 lbs will raise the gravity to 1.077 . That is what I would expect the first reading to have been assuming your volumes and quantities are as you have provided. An SG of 1.077 has a potential ABV of about 10% .

 

[kzufelt]

So - 15 lbs of honey is about 1.25 gallons (assuming 12 lbs = 1 gallon) .
25 l of water is about 6.5 (slightly more) gallons . Your total volume is then 7.75 gallons . Yes?
That is then about 2.2 lbs of honey per gallon. Yes?
One pound of honey will raise the gravity of 1 gallon of water by 35 points (1.035) so 2.2 lbs will raise the gravity to 1.077 . That is what I would expect the first reading to have been assuming your volumes and quantities are as you have provided. An SG of 1.077 has a potential ABV of about 10% .

A lot to unpack here, but I'll try my best, and thanks for the detailed reply.
25 litres is 5.49 gallons. That's is the measurement of the honey water mixture and not strictly water. (Sorry I wasn't clear on that).
Can you walk me through the calculations again with the new volumes?

(I just realized that there is a US gallon besides the regular gallon. Sorry if that screws with the calculations).

 

[bernardsmith]

OK - this increases the starting gravity a little but the same principles stand - if your volume (water PLUS honey is 25 L and if 25 L in the US is 6.5 gallons (An imperial gallon is larger than a US gallon) then 15 lbs of honey is divided into 6.5 gallons which means that every gallon must contain 2.3 lbs of honey. At 35 points per lb of honey the SG of the must will be 2.3 * .035 = .080 and an SG of .080 will have a potential maximum ABV of about 10.5 %. (.080 * 131) (approximately). Some batches of honey will have a slightly higher gravity and some batches may have a slightly lower gravity (depends on the amount of moisture in the honey )- but as a rule of thumb you can base any assumption on honey having a gravity of 1.035 when dissolved in water to make 1 US gallon.

 

[kzufelt]

Some batches of honey will have a slightly higher gravity and some batches may have a slightly lower gravity (depends on the amount of moisture in the honey )

When we took our honey to a starting beekeeper conference, we were told that it had a very high moisture content, (so high that it would almost not be considered technically honey). But your calculations were extremely helpful. Thank you.

I've been told that Nottingham yeast has an alcohol tolerance of around 10% ABV, so this might work out just right.

Just so I know I am not out to lunch, assuming your calculations for initial SG are correct (and I am sure they are), what should I expect for a final reading?

 

[bernardsmith]

I would expect a final reading would be 1.000 or even less (alcohol has a lower gravity than water so a mix of water and alcohol could have a reading of about .096.

 

[kzufelt]

Thanks bernardsmith. I'll take the new reading as soon as it stops bubbling and post it here if you wish.
Thanks for all your help.