January's fermentation experiment: making kefir

What is kefir? 
Kefir is a fermented milk drink that originated with shepherds of the North Caucasus region, who discovered that fresh milk carried in leather pouches would occasionally ferment into an effervescent beverage. It is prepared by inoculating milk with kefir grains. Traditional kefir was made in animal skin bags that were hung near a doorway; the bag would be knocked by anyone passing through the doorway to help keep the milk and kefir grains well mixed. Kefir has health benefits similar to yogurt and is excellent for digestion.


How to make kefir

• Purchase kefir grains online. I got mine here. Be sure to follow instructions for re-hydrating your grains if they have been dehydrated for packaging and shipping by the seller.
• Place grains in clean glass jar. One website suggest adding 8oz milk for every tablespoon of grains, add 7-8 ounces of milk but I didn't measure anything and my kefir turned out fine. I used a large mason jar filled about 3/4 full with milk on top of the kefir grains.
• Cover the jar loosely (I use a paper towel secured by a rubber band) and place at room temperature, away from direct sunlight.
• Kefir will form in 12-48 hours. It will have a thick consistency similar to drinkable yogurt and it should smell a bit yeasty. If the smell is rotten then something is wrong. If your kefir has separated into curds and whey, it has been sitting too long. 
• Strain the kefir using a colander with very small holes to separate the grains from the kefir. Cotton muslin bags, such as the type health food stores often sell as reusable tea bags, can be used to contain the kefir grains if you find that straining is too messy or difficult when you are working with small grains.  If using this method it is very important to ensure the bag stays submerged in milk as the bag will attract mold.
• You can return the kefir grains to the jar used to culture your batch and start the process all over again to make a new batch. Put your new batch of kefir in a sealed container and refrigerate for up to several months.

Two approaches to making kefir

• Double fermentation First ferment in the usual way by adding the culture to the milk and leaving for a period of time, 12-24 hours is the norm. Then strain out the culture and leave the kefir out to ferment more slowly for another 12-24 hours before putting it in the fridg
• Continuous fermentation Store your kefir in a large jar but don't put it in the fridge. As each new batch is ready it's added to the existing kefir in the main storage jar and then the lid goes on. The kefir will continue to ferment (it's a live food remember) and will get very sour and fizzy. If you feel inclined to try this you must always use a jar with a rubber seal that will allow excess pressure to escape, otherwise you run the risk of explosions!

Caring for kefir grains

• A cooler temperature slows the fermentation down and makes a thicker kefir too. Some people like to ferment their kefir in the fridge, leaving it for 5 days or more to compensate for the much slower fermentation process.
• Keeping your kefir grains in the fridge regularly can disrupt the yeast/bacteria balance necessary for the kefir grains to function properly make the kefir grains less efficient and reliable. 
• Spare culture can be stored for a time in a jar in the fridge with some milk. The fermentation will slow right down and you can store them for a few weeks this way. It's a good idea to rotate them with the grains you're using for your regular kefir making so that they get a chance to warm up and restore vitality to their microflora.
• To take a break from making kefir for a week, put the grains in the same amount of milk you use to make a batch of kefir and put them in a sealed container in the fridge for a week. If you need more than a week off, be sure to change the milk each week. Don't do this for more than 2-3 months.
• Kefir grains can be stored long-term by drying them.  Simply rinse the kefir grains with filtered water to remove all milk residue.  Lay them on a piece of unbleached parchment paper and set them in a safe place.  Kefir grains will generally dry in 2-5 days depending on room temperature and humidity levels.  Once the kefir grains are completely dry, they can be stored in a zip lock bag in a cook dry place or the refrigerator.  If possible, package the dried grains with a small amount of dried milk powder.  In this state, kefir grains will generally survive at least 12 months
• The biggest danger with leaving the kefir grains in the same milk for more than 48 hours is that they will generally begin to starve which damages the kefir grains.
• It is not necessary to rinse kefir grains between batches unless you suspect they have been contaminated.  Kefir grains often work better if they are not rinsed.

Additional notes

•  If you are culturing multiple products (e.g. different varieties of yogurt, buttermilk, kefir, Kombucha, etc.) be sure to keep a distance of at least several feet between cultures so they don’t cross-contaminate each other.  Over time, cross-contamination will weaken the culture.
• Kefir which cultures at room temperature for longer than 48 hours can have a laxative effect. 
• Kefir and kefir grains should not be stirred with or stored in metal other than stainless steel.
• Kefir sticking to the grains is normal and does not present a problem.  Just remove large quantities and don't worry about smaller layers of kefir that remain on the kefir grains as they go into fresh milk.
• The easiest way to find the kefir grains is to first stir the kefir well with a wooden or plastic spoon--you want to homogenized the kefir and break up the coagulated portions.  Next, pour the kefir though a fine mesh strainer and gently work the kefir through using  your fingers (be sure your hands are washed and rinsed well as both foreign bacteria and soap residue can wreak havoc on kefir grains).  This process should allow you to locate the kefir grains as well as homogenized the kefir.
• During the culturing process, kefir will generally go through three stages: Liquid milk, thickened liquid (generally the consistency of cultured buttermilk or liquid yogurt), thicker kefir (almost a yogurt consistency in some cases) and finally separated into curds and whey.  How quickly the kefir moves through the various stages is a function of several factors including room temperature and the ratio of kefir grains to milk.  Kefir that has separated is simply kefir that has over-cultured.  It is generally safe to consume over-cutlured kefir provided it looks, tastes and smells okay.

The above information and much more can be found here and here and here and here.