Kombucha overflowing (yes yes I know...)

[zarniwoop]

Ok I need to get this clear first I’m asking on behalf of my wife, I don’t “brew” kombucha I merely assist whilst drink my home brew.

But.... other half made kombucha, after reading the “add a bunch of fruit pulp and a spoon of sugar to each bottle and stick in fridge after 3 days” method of carbonation I decided we could do better than that. Took an estimate at the sugar in the raspberry pulp then bulk primed with the pulp and bottled (agitated whilst pouring to ensure even distribution of pulp) with a target of 2.5 CO2. Wife opened up a bottle after 4 days and it exploded over the kitchen but was only just carbed and not even close to what I was aiming for. So I now have a raspberry soaked kitchen and my wife being smug that the kombucha brewing woman on youtube was right and I was wrong (oh the shame!)

So what I’m really confused about is why it blew the top off but was barely carbed? Is this a case of too high a CO2 pressure but insufficient time in the bottle to carbonate the liquid or is something else going on?

 

[fdsaasdf]

did you chill the bottle first or open it at ambient temp? you'll want to chill it to ensure the liquid dissolves the CO2, otherwise it will all sit in the headspace

 

[Gollywog]

I presume you didnt leave it in the fridge for a few days for the C02 to infuse into the liquid?
In a warm bottle, the C02 wont have been absorbed.

Couple things to do in the future.
1) You measured the sugar in the raspberry pulp. Did you also consider the remaining sugar left over from the first ferment?
Take a refractometer reading of the Kombucha and then multiply the brix by .8. The reason for this is the bacteria have produced various acids that will screw with the correct reading of the refractometer.
2) I cant remember what the correct name for it is, but when you pulp the fruit and add it to the bottle, you will always get crazy foaming. It's something to do with the surface area of the fruit. Someone else will chirp in and provide the correct name for this reaction.
A possible solution is to give up one of your fermenters or large glass jars. Take the finished 1st ferment, add the fruit pulp (blended is better than whole) to the jar or fermenter, throw it in the fridge for a few days to infuse, then strain the fruit out and bottle. You will get all the flavour with none of the fruit to cause the foaming reaction.
When bottled, leave it in a warm spot for a few days to warm up and carbonate. Keep a plastic bottle filled with your finished Kombucha which you can use as a guide for when all the bottles are complete. I am making the assumption that your wife will be using glass bottles because the "lady on the internet" said not to use plastic. Food grade plastic is fine, the "lady on the internet" is wrong. Ignore her.

Source: I make Kombucha and sell it at the local markets.

 

[zarniwoop]

Thanks, very useful info.

Re chilling to infuse the CO2 I’ve never had that issue with beer?

 

[fdsaasdf]

Thanks, very useful info.

Re chilling to infuse the CO2 I’ve never had that issue with beer?

Do you drink your beer warm?

 

[zarniwoop]

Do you drink your beer warm?

Well I am English

Ah just read up on this and there is a relationship between CO2 absorption and temperature, I’ll need to dig up some graphs to see how much of a difference the 15ish C makes but I suspect this would result in just a little more carbonation and wouldn’t account for the massive difference between low carbonation and the bottle exploding. Sounds like the fruit pulp issue is the key.

 

[zarniwoop]

Just did a quick bit of reading and yes there is a fairly significant difference in the solubility of CO2 in water between room temp and fridge temp, probably an extra 50%, not sure how long you’d need to keep at the low temp to get this to happen?

Even considering this I think the fruit pulp is the most likely issue. Thanks for the advice

 

[Engibeer]

Yes, the fruit pulp is the most likely issue.

It's called "nucleation points" @Gollywog

Carb chart here for reference:

https://keg-king.com.au/wp/wp-content/uploads/2017/06/KEGKING-Set-Forget-CO2-Carbonation-Chart.png
An alternative is to blend the fruit pulp and then strain it through a fine nut-bag. This is what I do, and I don't have any issues with foaming.

I shudder to think how many people brew kombucha and bottle it in nice looking bottles that aren't pressure rated! All these loose and uninformed recommendations to use glass without the awareness of bottle bombs!