How to make yoghurt with your server
If you own a personal server, you are probably using it to perform many useful things: fetching your mails, hosting your personal web pages, connecting your local network to the internet, ... Now, you can also take advantage of its heat to make your own yoghurt.
Making yogourt is actually a dead-simple process. Take milk, add a little bit of yoghurt, leave it at a given temperature for one night, and when you wake up... It's all yoghurt. I wish more things could be obtained this way.
Disclaimer: Know what you are doing. I am not responsible for any damage caused on your machine, or for any improper use of the resulting product. Actually, one must be pretty damn stupid to think about making yoghurt in his computer. I am going safely through this process quite often, but in any case, do not eat something if you aren't absolutely sure it is safe.
Yoghurt contains bacteria (namely Streptococcus thermophilus and Lactobacillus bulgaricus) that take milk sugars as input and produce lactic acid as output, solidifying the milk in the process. These bacteries prolify best at a temperature of 42°C. Fermented milk is considered yogurt when it has at least 10 million bacteries per gram.
Hopefully, 42°C is the temperature of your server case or the place around it. We will take advantage of this overwise-wasted heat to produce something useful: yoghurt.
The essentiel parameter is your case temperature. Bacterias will start profilerate seriously starting from 30°C, the optimal temperature being 42/45°C.
What you need
- 1 liter of low-fat milk,
- 1 yoghurt that you'll find at your local store,
- optionally, a little bit of powdered milk,
- a server with a case temperature of 35-45°C (will also work with a workstation).
Bootstrapping the yoghurt
Put the milk into a large receptacle, drop the yoghurt, and mix them together. The process is bootstrapped. If you want your yoghurts to have a more "solid" state, you can add powdered milk at will. Now you can pour the milk into little pots that you will close.
Another way to bootstrap the yoghurt-making process is to directly buy the bacteria at your drugstore. However, a well-chosen commercial yoghurt will probably do as well. Try different ones until you find which gives the better results.
Let the bacteria proliferate
Now all you need to do is put the little pots into your "hot place". For instance, inside the case of this big box.
I also get very good results if I leave the pots on top of my OpenBrick: a small, fanless, noiseless server which aluminum case serves as a heat-pipe. So it is hot enough to make yoghurt - especially if I put them between the brick and its external USB hard drive.
If you put your yoghurts inside a case, close it for better results - if air circulates too much, the temperature will not be high enough. Tip: place your yoghurts close from a hot part, like your processor, a heat-pipe, or a heat sink. Be very careful not to spill the pot inside your machine! Some kind of hermetical system to close your pots is a necessary safety.
Bacteria will proliferate starting from 30°C, but the optimal temperature is 42/45°C. If you can monitor your case temperature, you may want to start a few processes to increase it in case it's not enough.
The time your yoghurts have to stay directly depends on the temperature. The closer to 42°C, the better. In the best case, 5 to 8 hours will be enough. If your environment is not warm enough, you may need to leave them 12, 16 or even (in extreme cases) 24 hours. You know a yoghurt is ready when it doesn't seem as liquid as the original milk. However, do not expect them to have the same texture as those you can buy at your local store. They will always keep this somehow liquid aspect, especially after being mixed.
"~" made yoghurt
And here they are, your own yoghurts! Now they should have this delicious acid taste. You can keep them in the fridge a few days, but I recommand eating them as soon as possible. You can also use them to make more yoghurt, by repeating the process. Once in a while, it may be desirable to start over again with a "fresh" yoghurt. Enjoy!