First time mead gravity question

[Jeff Covey]

So finally putting together my first mead batches. I'm doing a 3 gallon high gravity berry mead. Recipe for 3 gallon batch:
12lbs OB honey
3lbs Black Curran puree
8lbs triple berry mix
4lbs strawberries

After adding the honey and black currant puree, the gravity came in @1.155....which I was expecting. I added all of the fruit to primary on day two. Since my refractometer only goes up to 30 brix, I had to check the OG with the trusty hydrometer. After a week, I check the gravity with the refractometer and the gravity is coming in at 16 brix, which would mean it fermented down to 1.010 and close to 20% ABV. I assumed this was not correct, and re-checked with hydrometer and it's at 1.035 which is where I expected this to finish. So after doing some reverse engineering on these numbers(current gravity = 1.035 and brix = 16) that means the OG was really around 1.115 and I'm currently around 9%ABV. Is it possible that adding 12lbs of fruit in a 3 gallon batch could drop the OG by 40 points? If so, I'm guessing this is going to finish much drier than I expected and I'll probably have to do some backsweetening. Thoughts? I appreciate any feedback, I'm glad I found this forum.

Jeff

 

[bernardsmith]

I suspect that your original reading was likely close enough. Honey = 1.035 per pound per gallon. And refractometers are calibrated to measure the angle at which light is bent through water not through alcohol. When there is alcohol present light bends differently. You need to use a formula to recalibrate a refractometer when any alcohol is present. Formulas (and they are quite complex) are published in online calculators designed for just that purpose..

 

[MrTCS]

Refractometers require a calculation to get an accurate values once alcohol is present. You must know the OG and current values, then plug them into a calculator like this one.

 

[Jeff Covey]

I'm pretty sure my math is correct, I've been a homebrewer for years and I understand the adjustments that need to be made with a refractometer. I guess my real question is what would you expect the fresh fruit to do to the original starting gravity? I assumed that the juice imparted from the fruit would be significantly less than the 1.155. I just didn't expect that it would lower the full gravity that much.

 

[bernardsmith]

My rule of thumb is that fruit is likely to have the sort of sugar to water ratio of about 1 lb of sugar in one gallon of its juice - so somewhere around 1.040 -1.050 per gallon of expressed juice. Fifteen pounds of fruit - is that about a gallon or so of juice? So that would have increased your volume by 25% but increased the total sugar amount by say, .045 so 13 * .035 = .455 (honey) + .045 (fruit) =.0500 / 4 (gallons) = 1.125. If the volume of juice was greater or the amount of sugar in the fruit was less then the SG would have dropped more.