fruited sour carbing

The fruit will ferment and produce CO2. What kind of container are these in? Unless they are completely sealed, most of the CO2 is going to be lost to the atmosphere. And you don't want to ferment in something airtight unless it can handle the pressure.

 

I hope your glass jars can handle the pressure.

Google up the sugar content in ounces per pound of your particular fruit(s). You may need to convert grams to ounces, etc. Multiply what you found by 1.5 to get the sugar content per the 1-1/2 lbs that you used. Then go to a carbonation calculator, such as...
http://hbd.org/cgi-bin/recipator/recipator/carbonation.html or if you use BrewCipher, go to the Carbonation tab.
Enter the volume of your beer (1 gallon) and the temperature of your beer when you racked it to the gallon jar (or the highest fermentation temp it had reached before racking). Then...enter (tweak) the desired (override) CO2 volumes until the amount of sugar required (i.e. the calculator's answer) exactly matches the amount of sugar you had determined was in your 1.5 lbs of fruit. The desired/override CO2 volumes will be what you can expect in your final beer.

 

I would honestly let the beer sit on the fruit for a while - it takes a few weeks at least to get optimal flavor extraction and let the sugars ferment out, then carb normally with sugar. Easier, and much less risky. The thought of glass jars, carboys, whatever, under pressure freaks the fuck out of me.

That being said, if you were dead set on carbing with fruit, I would macerate the berries to create a thick syrup/juice and use that to bottle condition/carb with. Predictable sugars using Vike's resources above, and safe.

 

Too late to edit, but meant to add...
You could have a real foamy mess on your hands if you do this and then rack the carbonated beer from the jars to bottles, particularly if you do it at room temp.

Also, in my head, without doing actual math, 1.5 pounds of blueberries in one gallon of beer could blow up real good. So do the math.

 

It's not only the fermentation head space that you need to account for. The blueberries will take up a fair amount of volume. Don't rely on fruit for carbonation. Use something predictable like table sugar after you've let the fruit hang out for a while, like Stealth mentioned above.

 

Okay, I just now re-read an older post and see that you have an airlock on the jar lids. So once the fermentation of the fruit is done, the amount of CO2 in the beer will be the same as it would have been at the end of primary fermentation, i.e. just the residual CO2. So to carbonate your beer, you'd then use priming sugar as usual, to get whatever level of CO2 you're looking for.

 

I would let the fruit sit at least a month, ferment out to dryness, then use measurable amount of priming sugar to bottle condition. Priming with fruit fermentables is a gamble. How do you plan to measure the grams of sugar the fruit contributes as priming purpose?

 

I use glass carboys mostly, with an airlock. I was under the impression you had your jar completely sealed to contain all co2 created.

 

1 gallon batches have a much slimmer margin of error when it comes to carbing because smaller deviations in priming sugar quantity can create a bigger change in carbing compared to a 5 gallon batch. If you have an airlock on the fermenter then you will not get any "carbonation" from the fruit and as others have mentioned, you should allow the fruit to finish fermenting out before you attempt to bottle or you will have too many unpredictable sugars in your still fermenting beer and are almost guaranteed to have bottle bombs. You need to wait to bottle until the gravity has completely stabilized from the fruit sugars and then bottle.

If you are only making 1 gallon batches then you need ultimate precision in calculating your priming sugar, based on how much wort/beer you are carbing. Assuming you have exactly 1 gallon to carb with every batch and you add the same amount of sugar to prime each time could be your problem here...hops and fruit in your wort will rob you of some of your final volume, and will therefore require less sugar to prime compared to a full gallon. You will most likely need to rack your beer into a bottling bucket and then determine exactly how much volume you have before calculating your priming sugar and then adding it.

 

Has the gravity stabilized after adding the fruit? If not, don't bottle unless you want bombs/gushers. Once gravity has stabilized for at least a week or 2, add your calculated priming sugar solution and bottle as normal.

 

There really aren't any other methods/indicators without taking gravity readings. A refractometer would give you a reading with only a drop or 2 of beer, besides that you could drop a hydrometer in the gallon fermentor and retrieve it after you rack the beer for bottling or snag it if it's floating high enough at the top. Just one of the problems with 1 gallon batches. :/

 

You're worried about an infection? That ship has sailed, my friend.

Like usual, you should be looking for a stable SG reading over time, that will indicate fermentation is over.

If you have been overcarbing everything... are you using a calculator or a pre-measured sack-o-sugar from the LHBS? Its best to measure your own (by weight, not volume) and then make sure you calculate using the real volume, not the original volume of the batch. Spillage, measurement samples, and trub loss of volume may be the reason you are overcarbing.