Updated: Sep 2
Now that you have a batch of kombucha that has fermented to the point you like it, it's time for the fun part! This is known as F2. I don't put whole ingredients in bottles (anymore!). It might look pretty and seem easy to do so, but there are a number of downsides. Inconsistent carbonation, "expired" ingredients, and hard to clean bottles are just a few of them. I'm not going to tell you what to do, but trust me, this is so much better.
Flip top or other glass bottle rated for some pressure (if carbonating).
Funnel or bottle wand
Strainer or cheesecloth
Flavor ingredients of your choice (more on that later)
First things first, you need to fish out the pellicle and about 2 cups of liquid, stirring first. Do so with clean utensils, being careful to keep them completely soap free before putting them in your kombucha. Clean hands and utensils completely devoid of soap is a strong rule of thumb for kombucha. Keep this SCOBY liquid in another glass/steel/ceramic container with a cloth cover, this is what you'll use to make your next batch. If it isn't fairly mature (sour or fermented for over a week) you should let it sit for a few days before using it to make a new batch.
When choosing your ingredients, try to use ingredients that are as raw as possible. Many preservatives will kill your culture, and preserved ingredients don't taste as good anyways. Ingredients will taste different whether they are fresh, dried, cooked, etc. Play around to see what you like. A general rule if you need help choosing ingredients is to pick one fruit and one herb and see if they sound good paired. It offers a food source for F2 and will create something more complex than a 1-note sour fruit drink.
Now you're going to do what is technically a 1.5F because were putting these ingredients in the large container the kombucha is already in and not putting a lid on it (still a cloth though). If you have fruits, smash them up and stick them in (puree not suggested). Juice pours straight in. Herbs you should muddle or chop first. Spices can be crushed. Later on you can, and should, experiment with prepping flavor ingredients (like making simple syrups or roasting) but for now just do what is easiest. Here is a very general guide to ratios:
Fruits: Half a cup juice or smashed per "gallon"
Herbs, spices, teas, tisanes: 2 Tablespoons per "gallon"
"Gallon" can be a full gallon or minus your 2 cups for next time.
The strength is very subjective, you'll figure out what you like after the first batch or two.
Now you'll let your ingredients sit in the booch at least overnight, if you have ingredients that can oversteep and you don't want them to, strain them around when they would start to (8 hours is usual). Otherwise, strain between 12-24 hours depending on when you like the infusion.
If you don't want to age or carbonate, you can stir and pour into bottles! Otherwise, heres the next step.
I'll go over aging first because carbonating is an issue for a lot of people. The longer ingredients ferment or sit, the more they change and meld with the culture. There are three forms of aging: aerobic ferment, anaerobic ferment, and cold aging. You can do any one or combination of them.
Aerobic Aging: Aerobic means the culture ferments the way it has been the whole time, with oxygen. All you have to do is strain out your ingredients and let it sit with the cloth. The longer you do this, the more the nutrients and compounds of your ingredients are eaten by the SCOBY. It will also make more acids and become less sweet and more sour. It's the same process that your tea went through. There is a way to do this while keeping acid levels but it is beyond the scope of this topic.
Anaerobic Aging: Room temperature with lid on. This is also how we build carbonation past natural effervescence. High temps and long time periods will increase alcohol and possibly dangerous levels of CO2. The ingredients still meld and ferment during this process.
Cold Aging: Cold aging is letting the bottle sit in the cold. I always suggest to let the bottle sit in the fridge at least two days to incorporate flavor, CO2, and acidity. There is still minimal fermentation during this process. Cold aging for long periods can be difficult but the end product is usually more complex or tastier.
The biggest topic when it comes to homebrewing. People often struggle to get their carbonation to the level they want to. I'm going to share every tip I can think of to help get your process down.
1) It may be 1 day, but it may also be 10. There are a lot of factors that come into play in carbonation. Depending on how many of those are in favor of carbonation or not, you may have this large discrepancy between carbonation times. These tips will tell you how to avoid the mystery of time.
2) Use a test bottle. There are two types of test bottles. The first, slightly less practical for beginners, is taking one of your many bottles after a certain amount of time, cooling it down, and opening it to see if it is carbonated. If it isn't don't put the rest in the fridge yet! The second kind of test bottle, is filling a BPA free water bottle. I know what you're thinking: but it's plastic! As long as you aren't leaving the kombucha in it for a long amount of time, and you replace the bottle often, it will be ok. And don't use super cheap and thin bottles. This method is great because you can squish the bottle to see how much pressure has built up. If it is firm, you can try cooling it down and opening it to see exactly how carbonated it is. If it's rock solid immediately refrigerate your other bottles and be careful, you probably let them overcarbonate.
3) Factors of carbonation. Warmer temperatures increase carbonation. Strength of culture from F1 increases carbonation. Residual or added sugar increases carbonation. Wild yeasts, enzymes, and nutrients increase carbonation (like ginger, pineapple, and tea respectively). Amount of yeast and stirring will increase and even out carbonation. These are the main factors, and I'm not saying they are things you have to do, but be aware for your time.
4) I'm not getting carbonation. You're missing one of the factors above or not giving it enough time. Is it really cold in your house? Made sure to add a little sugar, especially if you didn't add fruit? Were you using clean but non-chlorinated water? The only cause beyond the factors is bottle seals, every once and a while bottle seals will be faulty and need to be replaced.
5) Ingredients in bottles mess with carbonation. Any solid in the bottle creates nucleation points, points for carbonation to stick to instead of dissolving into your liquid. It makes your carbonation come out of the bottle when you open it, either causing explosions or making your carbonation release all at once.
6) Refrigerate your bottles. Cold bottles leads to carbonation dissolving into your liquid, reducing the chance of overflow when you open a bottle and making the fizz last longer in your liquid.