When you first start using a cob oven, you see the heat stored in the oven wall as an opportunity. The list of things you can cook in them is massive.
When oven days arrive, you will find yourself having a row of items waiting to take their turn in the oven as the temperature slowly drops and hits the best temperature for that particular food.
Once the main foods are cooked, the mind gets to working out what is next. Dehydrating things eventually enters the conversation, as it did for us here.
We found that cob ovens can dehydrate food. However, there are safety precautions that you should consider. This post is about the drying process using a cob oven.
How cob ovens work.
Cob ovens are straightforward pieces of equipment. They are heated up internally with fire, and then once the fire is removed, the oven can be used for cooking first, and then things like dehydrating can take place when the heat is not so intense.
It is through the release of stored heat from the oven walls that allows the food to be cooked.
Different types of cob ovens.
There are two basic designs that exist as far as we know. The first is where the fire is lit within the oven chamber and is kept stoked until the oven walls have absorbed enough heat to allow for food cooking.
The second kind of oven is fed hot air via a chimney from a fire pit below the base of the oven. This is the oven that we built and have the most experience with.
When do you use a cob oven to dry food?
Cob ovens can be used for dehydrating food when the oven temperature has fallen below a cooking temperature.
Because of how the cob oven works, the oven is at its highest temperature and beginning its descent when you cook food. How fast that drop depends on the quality of the cob mix and the wall thickness.
A high-quality oven will hold a temperature longer than a poorly designed and built oven. We have an article titled “How do you design a cob oven?” that details this topic. It also links to several more detailed pages on specific attributes desirable in a cob oven build.
Once the temperature falls a few degrees, it cannot return to that higher temperature unless a fire is re-introduced.
This pattern is repeated at every temperature change until the oven returns to its ambient temperature. This describes the standard type of oven. The other kind of oven is called a rocket stove cob oven, which is an entirely different animal for cooking.
To understand these two very different ovens, we have written an article that describes them both in detail here. It is titled “Cob oven vs rocket stove cob oven (what best suits you?)“. If you are thinking of building a cob oven, we recommend it to you.
Does food dehydrate well in a cob oven?
Food can dry very well in a cob oven if the air flow is effective enough to remove the moist air from the oven chamber.
To create this airflow, it is beneficial to have a chimney that can be adjusted either open or closed and anywhere in between.
The oven door may need to be slightly ajar to allow fresh air to enter and replace the hot air that has taken on some of the moisture from what you wish to dehydrate.
Our oven (rocket stove fed) has hot air entering the oven chamber from below, and it exits via a vent at the rear of the chamber at floor level.
This creates a good airflow for drying, and we can usually leave things to dry overnight as the oven slowly cools down. It is often still warm the following morning.
How long does it take to dehydrate food in a cob oven?
It can take as little as a few hours to as long as 1 1/2 days to dry some foods. The longer times should be for foods that are more forgiving for a range of temperatures because it is difficult for an oven to maintain a specific temperature for extended periods.
The shorter the required time frame the better the result with a cob oven.
We often dehydrate Thai chilies once we are done cooking the main foods and make a mango puree toasted muesli at the same time. That is a fantastic breakfast.
Are there benefits to dehydrating food in a cob oven?
The primary benefit of dehydrating food in the cob oven is the energy saved in the drying process. The heat is already banked in the oven’s walls, so it makes perfect sense to take full advantage of this stored energy.
The other beneficial thing is it is silent. No motors or fans are running, and the amount of food to be dried is irrelevant. The heat is there to be used, so use it.
What disadvantages are there in using a cob oven to dehydrate food?
A primary disadvantage to using the cob oven as a food drying unit is the inability to maintain a temperature for extended periods. This does limit the types of food that you should dehydrate.
There is an elephant in this room with us, and that is knowing your oven.
Every single cob oven has its speed of temperature movement that we will call heat decay, for want of a better term. It will take many uses of your oven before you understand your oven’s heat decay profile.
Once you know this, only then will you be able to dry food in your oven safely.
The final words here on this post are pointed toward the safety side of the topic of this post. Some foods take days to dry and can be a risk if not dried in a controlled way.
These foods are best left to the dehydrator machines that can regulate the temperatures for as long as needed. The cob oven cannot regulate temperatures well, so it is wise to stick to drying small items that only need hrs and not days. Sometimes you may want to dry non-edible items, and we list a few ideas in “What can be dried in a cob oven?“
Article by Tim Blanch for TheTropicalHomestead.com. He is a qualified Permaculture designer.