Fermentation – Page 18 – Urban Fermentation

Once you begin making kefir you may find that it has small bubbles in and around the grains. This is especially noticeable when it is warm. These bubbles are made of carbon dioxide, the gas used to carbonate soda. It is natural and nothing to be concerned with. It is natural for kefir to be slightly fizzy when it ferments. The yeasts and lactic and acetic acid bacteria found in the grains produce carbon dioxide as a byproduct of fermentation. Some of this gas gets caught in the milk and on the grains giving it an effervescent quality. It is this gas which makes the kefir fizzy. If kefir is fermented in an aerobic environment the carbon-dioxide will mostly dissipate into the air leaving the kefir only slightly fizzy but if the kefir is fermented in an anaerobic environment the carbon-dioxide can build up and pressurize the container. Fermenting kefir in an aerobic environment When your kefir grains produce an overly fizzy kefir in an open container then your kefir has too many yeasts actively converting lactose into CO2. There could be several reasons why this occurs. The kefir is too warm The main yeasts which are in the kefir cultures are Saccharomyces cerevisiae, S. unisporus, Candida kefyr, and Kluyveromyces marxianus ssp. Marxianus. All of which are yeasts which are most active at higher temperatures. This means that these yeasts will produce a higher amount of CO2 making the kefir fizzier. To correct this find a place to ferment your kefir in a cooler place. This will slow the growth of the yeasts which will in turn produce less CO2. It may take a few batches for the kefir to become less fizzy as the culture rebalances from the change in temperature. High amounts of fermentable sugars in the solution. Yeasts grow really fast when there are lots of available sugars (lactose) in the solution. Yeasts use simple sugars and carbohydrates for energy. This is why yeasts are used in the production of bread, the yeast grows fast when provided with enough food. The sugar in milk is lactose which comes in two forms a monosaccharide and a disaccharide. It is water soluble not fat soluble. So when there is a higher content of fat in the milk there will be less fermentable sugars for the yeasts to use for food. Skim milk has a higher amount of lactose per cup then milk with has a higher fat content simply because the fat content in the milk takes up space displacing the non-fat contents which contain the lactose. The ft in the milk needs to be broken down into simple sugars. This takes time which slows the fermentation process down. So if you find your kefir is too fizzy for you then try using milk with a higher fat content. Not only does this slow the yeast down but it also will make a thicker creamier kefir which is great for smoothies and making kefir cream cheese. Imbalance between yeasts and bacteria Kefir is fermented with a symbiotic culture of bacteria, yeasts. To get good tasting nicely balanced kefir the proportion of the yeasts to bacteria needs to produce kefir which you enjoy. What this balance is will be dictated by your personal preference. If the culture is dominated by yeasts then the sugars in the milk will be consumed mostly by the yeasts producing high amounts of CO2. This can happen for a variety of reasons. Regular long fermentation time If you regularly leave your kefir grains longer than the 24 hours recommended the yeasts in the kefir may become overpopulated. This is because the yeasts in the culture have a greater range of tolerance to acid then the lactic acid bacteria (LAB). It seems a little counter intuitive that the LAB do not thrive in an acidic solution until you think about it a bit. LAB convert sugar and alcohol into lactic acid. The acid is a waste product produced by the LAB which remains in the solution. The yeast on the other hand produces CO2 and alcohol. The CO2 dissipates into the air and the alcohol is used by the LAB as energy. Therefor the waste products which the yeasts make do not overwhelm the solution, allowing them to continue to grow reproduce longer. This gives the yeast culture a head start when exposed to new milk, overwhelming the LAB growth and making the kefir extra fizzy. High ratio of kefir grains to milk The amount of CO2 which is produced is directly proportional to the amount of yeast bodies in the solution. Even if the grains have a good balance of bacteria and yeasts the extra yeast can ferment the sugars quickly. This will make your kefir fizzier because there are more yeasts available to quickly produce CO2. The action of the abundant yeasts continues as long as there are easily fermentable sugars. Fermenting kefir in an anaerobic environment To ferment kefir in an anaerobic environment you need to place your kefir into a sealed container. This limits the amount of oxygen which is available to the various cultures in the milk. Warning: Fermenting sugar with yeasts can produce a high amount of CO2 which can reach exceptionally high levels of pressure. If the containers which are used to contain an anaerobic fermentation is not meant for holding pressure they can burst and cause serious injury. Do not ferment kefir in normal glass containers with sealable lids. If you are fermenting kefir in an anaerobic environment be sure to use containers either release the pressure created by the CO2 produced or are designed to take the pressure. Fermenting kefir in an anaerobic environment has two aspects. Primary fermenting with grains Primary fermentation with grains without oxygen can be done a variety of ways. Some people simply put a lid on the Mason jar they are fermenting the kefir in rather than a cloth or some other permeable barrier. Some use airlocks which are used in the wine of beer making process which allow one way flow of the gasses produced by the fermentation. If you use the first method you will produce a kefir which is fizzier then the other simply because you will contain the CO2 which is produced rather than releasing it into the air, but both methods will produce a higher amount of CO2. Since the milk thickens because of the reduction of PH to about 4.6 and the lactic acid bacteria do not need oxygen to grow the milk still thickens into kefir. The difference between fermenting in an oxygen rich environment and an oxygen deprived environment is the efficiency of the yeasts. Yeasts can survive and grow in an anaerobic environment but their respiration is not as efficient. This produces more waste products, CO2 and alcohol. With a higher amount of CO2 produced comes a fizzier kefir. This means that when you ferment kefir in a sealed container the resulting kefir will have a higher amount of CO2 as well as a higher alcohol level. Secondary fermenting with additional sugars The concept of secondary kefir fermentation is as simple as adding some type of additional sugars to filtered kefir which does not contain the kefir grains. It is great to add additional flavors to your kefir. Make the kefir resemble a soda rather than a milk product. When making a carbonated kefir drink the kefir cultures which are left in the kefir after removing the grains use the sugar in the flavoring to grow rapidly. This produces a high amount of CO2 which is contained and goes into solution. The flavoring can be anything from fruit juice, coconut water or even sweet tea, anything which has easily fermentable sugars can be used. Again be sure you use bottles which are meant for holding pressure otherwise you may burst the bottles causing a huge mess as well as possible injury from flying debris. This makes a great kefir soda which has active cultures in it and a lower amount of sugar. It can be flavored with any flavor you like and can produce a slightly fizzy to highly carbonated beverage. The level of carbonation will depend on the sugar content of the flavoring, the temperature and the amount of time it is left to ferment. To get this how you want it you will have to do some experimentation. For the first few times you do a second fermentation open the bottle in a location which doesn’t matter if it over flows the container. Sometimes it can spew the bottle contents great distances which can easily hit a ceiling and end up all over walls.