Do Light And Heat Help Fermentation? Full Guide

Hands pushing cabbage down in a fermenting jar with a spoon.

If you have ever fermented something at home, whether it be a sourdough starter, beer, kombucha, or something else entirely, you have probably found yourself asking: do light and heat help fermentation? What is the ideal environment for fermentation?

Light does not help fermentation, but heat does. While fermentation requires a dark environment to truly thrive, having a warm environment for the fermentation to take place in will really help the process – it should not be too hot or too cold, just warm. 

Heat will help the fermentation process, but light will not. Let’s take a closer look at exactly why heat and darkness can aid in fermentation but light does not, and how to create the perfect environment for fermentation.

Does Sunlight Help Fermentation?

Sunlight does not help the fermentation process. While fermentation requires a dark environment to truly thrive, warmth will also really help the process. It should be neither too hot nor too cold.

The bacteria that do all the work when it comes to the fermentation process are called lactic acid-producing bacteria, otherwise known as LAB.

The lactic acid-producing bacteria are very negatively affected by sunlight. The UV rays from the sunlight more often than not will end up killing the lactic acid-producing bacteria.

Due to sunlight being so harmful to the lactic acid-producing bacteria, and therefore being harmful to the fermentation process as a whole, it is generally advised that when fermenting anything, it should be kept in a dark room or a shady area. 

TIP: If you are unable to store whatever it is that you are fermenting in a dark area, at least make sure it is an area that will always be out of direct sunlight.

If you live in a city where you do not get much natural sunlight in certain seasons, it would be fine to leave whatever item that you are fermenting on your kitchen counter as long as you know for a fact that your fermenting item will remain out of direct sunlight.

Jars fermenting on a shelf.
Make sure your ferments are not in direct sunlight

Does Heat Help Fermentation?

Fermentation actually requires a certain level of heat for the process to take place efficiently. The heat will help in the fermentation process up to a certain point – and after that, it may become harmful.

Fermentation processes thrive in a warm environment. For example, if you are fermenting a sourdough starter, wrapping a cloth around your jar may help the fermentation process go quicker than it normally would have without the extra warmth. 

NOTE: The ideal temperature for a room at for fermentation would depend on what it is that you are fermenting, as different fermentation processes require different heats.

If you are fermenting homebrew (beer, for example), the room should be somewhere between 90ËšF to 95ËšF (which is 32ËšC to 35ËšC).

However, if you are fermenting vegetables, the ideal temperature of the room you are fermenting the vegetables in would be around 70ºF (which is 21 ËšC ). The room shouldn’t be warmer than 72ºF (22 ËšC) or cooler than 68ºF (20 ËšC)

When the room is too warm, the yeast in the fermentation process may become overly active. If the room is too hot, the yeast could die, making the fermentation process completely inactive. This room thermometer from Amazon can help you be sure of the specific temperature where you are storing the ferment.

This means that you will see little to no results, as the yeast will not be working hard enough for any fermentation to take place.

Not only does heat help fermentation, but without enough heat, fermentation may not take place at all. If it does, it may be in such a small amount that you won’t even be able to tell that it is fermenting.

If the temperature in the room that you are fermenting is too cold, the yeast you are working with will become sluggish and “lazy.†

What is the Ideal Environment for Fermentation?

Fermentation is not necessarily complicated; however, it does require a few specific conditions in order for the process to take place as well as it possibly can.

The environment in which the fermentation process takes place is probably the biggest factor in what the results of the fermentation will be – because of this, it is very important to make sure you have the ideal environment ready and available for use.

As discussed above, the fermentation process does not do well in light, which means that the first aspect that is important in the ideal fermentation environment would be darkness.

Having a dark environment helps the lactic acid-producing bacteria thrive, meaning that your fermentation process will thrive too.

The second aspect that is crucial when it comes to fermentation is the temperature of the room. As we discussed above, the ideal temperature of the room will vary depending on what it is that you are fermenting.

TIP: Finding out the ideal temperature for the item you are fermenting should be the first step that you take, and once you have figured that out, you will need to try to find a space in your house that is as close to that temperature as possible.

To sum it up: the ideal environment for fermentation is a dark place with the right temperature. It is not complicated; it may just be a bit of a tricky process trying to find the space with these conditions!

What Can I Do to Speed Up Fermentation?

Fermentation is mostly a waiting game. It is not something that can be quickened or rushed or forced to go faster than it can.

The bacteria needs time to work, and the yeast also needs time to feed in order to produce all of its sought after goodness – it cannot happen overnight.

However, if you need the fermentation done quicker than usual for whatever reason, here are a few things that you could try to speed up fermentation:

  • If the fermentation recipe requires you to add yeast, you can add slightly more yeast than is required – the more yeast that is at work, the quicker the fermentation will go.
  • Turning up the heat ever so slightly (for example, wrapping a blanket around the jar) could help assist the yeast in being more active – they will feed on the sugars and starches faster, though, so be sure there is enough food for them.
  • Add less salt if you are fermenting vegetables – the salt will slow down the fermentation process, so by adding less salt, it will go faster by default.
Fermentation takes time even in the best of conditions

NOTE: There are not many things at all that will speed up the fermentation process or give you overnight results, so the best thing you can do is have patience.


Fermentation can be a delicate process since you are dealing with bacteria, and knowing what helps the process and what does not help can make or break the end result.

While light does not help with fermentation, heat does, so use this knowledge wisely.

Keep the jar of whatever is it that you are fermenting in a dark and warm environment, as it will help the process thrive and will give you the best chance of getting the results that you are after in the final product.

And at the end of the day, fermentation needs time, time, and more time. It is a relatively long process, but it is well worth it in the end.

As much as you may want to set up your fermentation one day and wake up the next day to a finished product, this is unfortunately not the way this process works. So set up your fermentation process, then sit back and relax, because the end results will be worth your time!

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