Temperature plays a really big role in your fermentation
cycles — both in first fermentation/F1 (in your brew vessels)
and second fermentation/F2 (if you bottle your kombucha).
And in general, the rules of kombucha temperature are the
same in both F1 and F2.
You want your brew vessels and bottles to be ideally in
the mid- to high-70s Fahrenheit.
But it will still ferment fine between the 65 - 85 degree
range. You may just need to adjust your fermentation time
accordingly. In general:
the cooler it is, the longer it’ll take to get more acidic.
the warmer it is, the faster it’ll ferment and acidify.
I like to use simple, affordable temperature strips* which I stick onto the outside of my brewing vessels. They help me monitor the average room temperature where my vessels are located.
I’ve found that in general, they work well enough for my purposes. The strips react to the temperature by “lighting up” the section that indicates the current temperature. They work sort of like a mood ring or glow-in-the-dark sticker so they don’t require batteries/electricity and don’t take up any space at all. I like them better than a probe thermometer, because that means I can just check on them without opening my brew vessels and without messing around with my SCOBY or kombucha liquid.
You may run into a few minor difficulties with using them — sometimes 2-3 of the temperatures will “light up” so you can’t tell which one the actual temperature is. Or sometimes none of them light up or light up only faintly. I often find that just running my hand along the temperature strip helps “re-activate” it and then the correct temperature will glow more brightly than the others. If you find that two are lighting up right next to each other, that means the temperature is right between the two.
Luckily, with kombucha, it doesn’t need to be terribly precise, so I find that these strips work just great for my needs.
Accommodating for low temperatures
It’s not always possible to keep our fermentation environment at the perfect temperature range. The good news is that kombucha is fairly hardy as long as you know what to look out for and can accommodate to “overcompensate” for potential areas of weakness.
So in the winter months, it may take longer for your brew to ferment because the temperatures are lower so the yeast and bacteria are less active. Because of that, it may take a really long time to ferment, or if your brew doesn’t acidify fast enough, you might get mold.
If your brew has gotten to the point where it’s acidic enough to bottle, you it's really unlikely that mold could enter the picture at that stage. But it may take longer than average for your bottled kombucha to build up carbonation.
You can help accommodate for this by using any (or a combination of) these tips when the weather starts turning colder:
Use extra starter tea — try doubling the amount you usually use. This will help acidify your brew and give it a good head start. The acidity will make it less susceptible to mold and it’ll help with decreasing the length of your fermentation cycle.
Use string lights (Christmas lights) to wrap around your vessel to warm it up. Be sure to wrap it all the way around your vessel — not just at the bottom. Otherwise, you’ll over-stimulate the yeast which likes to settle at the bottom of the vessel. This could lead to an over-abundance of yeast. Too much yeast isn’t the end of the world, but your brew will not taste right and you’d have to do a lot of back-pedaling to get your brew back into a healthy balance.
Other homebrewers may suggest seedling mats or heating mats to place under your brew vessels to keep them warm. This may work for you, but I don’t recommend it because of the yeast-overabundance issue I outlined in the previous bullet point. If you use them, try to wrap them around the whole vessel for an even distribution of heat.
Keep your brew vessels/bottles near the heater/furnace.
Have patience — unfortunately sometimes your brew just needs to do things on its own time. As long as you don’t see any mold, that means it’s trying its hardest to acidify for you. Sometimes you’ll just need to wait it out.
Accommodating for high temperatures
In the summer months, your brew may ferment faster because of the high temperatures. This could also mean that during F2, your bottles will produce carbonation faster, so you may not have to F2 at room temp very long before moving to the fridge. You don’t really have to worry about killing your SCOBY unless the liquid reaches above 100 degrees F.
If this happens, you could:
Move your vessel to the coolest, darkest spot in your home. It’s OK to keep it in a closet and just take it out at night when it’s less hot.
Keep it near an air conditioning vent.
In extreme cases, you could refrigerate your brew vessels (just for a few hours at a time) to bring the temperature back down before bringing back out to room temp.
There’s less you can do to accommodate for extremely hot temperatures, so in this case, you may just have to adjust your fermentation time and bottle it sooner before it gets too acidic. If you find that your brew got away from you and got too acidic — no worries! You don’t have to throw it out. You can use it as super-strong starter tea to use for a future batch of kombucha (it's great for that!). Alternatively, you could add some sweet tea or fruit flavorings to it to help balance out the acidity and drink it/bottle it up.
If you’re using these methods to alter temperature, be sure to always monitor your brew vessels to make sure you’re not going too far in one direction.
*On this page, you’ll find some affiliate links to sources where I’ve purchased my ingredients/materials that I use. I may get a small cut of Amazon's profit for finding + recommending them to you. It won't cost you any more than you’d normally pay for them. I went through a lot of trial and error to find low-cost, high-quality options to save us all money. But feel free to purchase from wherever you like!