The fermentation bee in my bonnet continues this week with a short discussion on the fermentation of milk. I reckon because milk is so easily accessible, and because it is a well-known and versatile product, it is probably a better topic for a column than something strange and exotic like koji.
We Namibians are familiar with fermented milk products: Dikmelk, suurmelk, Omaere, yogurt, Oshikandela (commercial drinking yogurt), Omashikwa, mashini ghakushika, mabisi (all traditional products from the north-central regions) and Âudaï (popular in the //Karas region) are all examples of milk that has been fermented. Furthermore, butter made by the traditional method is often also ‘cultured’ as it is inoculated with bacteria residing in the calabash used for churning.
Traditional fermented foods make use of spontaneous fermentation techniques in which the micro-organisms associated with raw food and the processing environment serve as inoculants. Inoculation is mostly by way of ‘back-slopping’, ie making use of samples of a previous batch to start the fermentation of a new batch.
Omashikwa (fermented buttermilk) is fermented using specific plant material; either omunkuzi (boscia albitrunca) or omukwa (adansonia digitata) roots. Back-slopping is another method.
After the introduction of the plant material, the milk is left to ferment for three to four days at ambient temperatures, commonly ranging from 30°C to 37°C. Then the roots are removed and fermented milk is churned by shaking the calabash for two to three hours until butter granules accumulate on top of the sour milk. Butter is then scooped off using a wire mesh or hands, and the butter granules are then washed using clean cold tap water to remove excess milk. The churned milk (omashikwa) is usually kept in plastic containers until consumed.
Mabisi (common in the Zambezi region) is prepared by collecting fresh milk in a calabash and leaving it to wild ferment for about four days at ambient temperature. Whey is then removed from the fermented milk, and more fresh milk is added. The process is repeated until the container is full of partly-drained curd. The whole process takes about a week.
The concentrated fermented milk may be shaken before consumption and kept for up to one week at room temperature. Âudaï is sour milk produced from goat milk. Generally, Âudaï is prepared by placing goat milk in a calabash and leaving it to stand overnight to allow fermentation at room temperature. The fermented milk is then poured into plastic bottles the next day for daily use (see Misihairabgwi and Cheikhyoussef [2017] for a review of these traditional processes).
While widely in use, these traditional methods are inefficient and inconsistent, meaning that they render low yields and inconstant quality products. On the upside, the benefits of these fermented foods include better taste and enhanced nutritional quality as well as an improvement of the shelf life of the food.
Milk kefir and yogurt are two fermented milk products that use special starter cultures to start the fermentation process. Both are rich in probiotics and offer significant health benefits. Both are also easy to produce in a home kitchen with just the most basic equipment.
There are important differences, though. First, milk kefir is a mesophilic culture, which means it cultures at room temperature, regardless of which type of starter culture you use. Most popular is the use of kefir grains.
Yogurt starters on the other hand can be either mesophilic or thermophilic. Mesophilic starters are cultivated at room temperature, whereas thermophilic starters are heat-loving and are best prepared in a yogurt maker or similar appliance. It will culture at around 42ºC.
Second, both kefir and yogurt have live bacteria that have significant health benefits. The bacteria in milk kefir can actually colonise the intestinal tract. Kefir also contains a far larger range of bacteria than yogurt, in addition to containing yeasts. The beneficial bacteria found in yogurt help keep the digestive tract clean and provide food for the friendly bacteria found in a healthy gut. They pass through the digestive tract and are called transient bacteria.
Kefir is generally more tart than yogurt. Both are versatile food and ingredients that could be used in many dishes from salads (as a dressing) and rusks to smoothies and frozen desserts.
• 1 1⁄2 cups sugar
• 2,5 kilograms self-raising flour
• 5 teaspoons baking powder
• 1,25 litres kefir (or buttermilk)
• 500 grams nutter
• 1 teaspoon salt
• 4 eggs
• Sieve baking powder, salt and flour together to mix well. Grate the butter and run into the dry ingredients using your fingertips. In a separate bowl, beat the eggs and add the sugar. Stir until the sugar is dissolved. Add the egg mixture to the dry mixture and mix well. Add the kefir and mix until a dough has formed.
• Pre-heat your oven to 180˚C. Prepare bread tins for baking using butter, lard or anti-sticking spray. Pinch balls the size of golfballs from the dough and put them in the bread pans. Bake for one hour. Remove the tin and set aside to cool.
• Preheat your oven to 80˚C. Break the rusks into individual pieces and add back to the oven. Dry the rusks to your taste. This should take between four and five hours.
