Easy homemade thick yogurt recipe, better than store bought

Time:         prep. 5 mins
                   cook. 15-20 mins
                   ferment. 4-8 hrs
                   cooling. 12 h
Difficulty:  easy
Yield:         for 4 servings
Cost:          very low

Do you like yogurt? Do you eat it frequently? If the answer is yes, you’re doing the right thing.
Consumed in moderation (one portion per day), it is a food with important functional and healthy characteristics.
So I think it’s worth learning a tried and tested recipe for an excellent homemade thick yogurt: we are used to buying it in plastic cups, but yogurt is one of the oldest fermented foods that exists in human history and deserves a little more respect; let’s not forget that through self-production we will also consume less plastic (see study on this issue), pollute less and have a high quality product at a lower cost!

History of yogurt

Yogurt only became popular in the western world after the early 1900s, thanks to the discovery of lactobacillus (the discoverer, Bulgarian doctor Grigorov, called them Lactobacillus bulgaricus) and the subsequent book ‘The theory of longevity by yogurt’ written by Nobel prize winner Metchnikoff; but there is evidence of its existence well before 5000 BC (some even speak of 10-15,000 BC).
There are no written records, but it is believed that yogurt was commonly consumed in Mesopotamia and from the steppes of Central Asia to the Middle East; perhaps this was more due to its longer shelf life than milk, but the fact that its nutraceutical properties were already known in antiquity cannot be ruled out.
Several etymologists (and even reputable sites such as Harvard University) attribute the word yogurt to the Turkish words ‘yog-ur-mak’ or ‘yogun-las-tir-mak’ respectively ‘to knead’ and ‘to thicken’; but after more specific research I came to the conclusion that yogurt may also derive from the old Turkish word complex ‘(u)yu-gur-t‘, which together summarise a food product made by fermenting* milk.
(*As is still the case today in Anatolia and in several Central Asian countries that speak ancient Turkish, fermentation is expressed by the term “putting milk to sleep”, which sounds very appropriate if you think about it: in fact, to achieve fermentation, milk – or something else – is put in the dark and under blankets)⁽¹⁾.

Nutritional properties of yogurt

Research shows that regular use of yogurt can have beneficial effects on the intestinal microbiota, teeth and skeleton; promote longevity and better ageing; and help against lactose intolerance. Regular consumption of yogurt has also been associated with a reduced risk of gastrointestinal, inflammatory, cardiovascular and respiratory diseases, as well as allergies, obesity, osteoporosis or type 2 diabetes and metabolic syndromes in general ^{(2, 3, 4, 5)}.
Not only because yogurt is very rich in nutrients and is an excellent source of proteins, vitamins (A, D, B5, B2, although B12 in smaller quantities) and mineral salts that are essential for the body, such as calcium, iodine, magnesium, potassium and phosphorus; but also because it is a perfect probiotic that can provide important nutritional and health benefits ⁽⁶⁾.

What’s in yogurt?

Yogurt is nothing more than milk that has been coagulated through lactic acid fermentation. Technically (and legally), in order to be called yogurt, this slightly sour-tasting substance should contain the two live bacterial strains of Streptococcus thermophilus ( aka Streptococcus salivarius subsp. thermophilus) and Lactobacillus bulgaricus (known as Lactobacillus delbrueckii subsp. bulgaricus) in abundance (more than 10 million per gram ⁷). However, in addition to these two, other micro-organisms may also be present, in order to give desired characteristics to the final product: such as Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus lactis, Lactobacillus jugurti, Lactobacillus helveticus, Bifidobacterium longum, Bifidobacterium bifidus and Bifidobacterium infantis ^{(8, 9, 10)}.

Choosing the ingredients

A homemade thick yogurt can be made from cow’s milk or a mixture of various milks, including cow’s, sheep’s, goat’s and even buffalo milk, all of which are suitable for their concentration of protein, fat, lactose and non-fat dry matter; obviously sheep’s and goat’s milk are a little more flavoursome and less appealing to everyone: if this is the case, start with at least a 50/50 proportion of cow’s milk.
You can use as starter, a homemade yogurt, a store bought one or specific starter culture from your pharmacy.

Preparation steps

1) Heat treatment

The first step in the homemade yogurt process is the heat treatment, for which we have 3 different options:

– 5-10 minutes at 95°C

– 10-15 minutes at 90 °C

– 20-30 minutes at 80-85 °C

Obviously, high temperatures for long periods of time inexorably reduce the nutritional properties of the milk. For this reason, I strongly recommend that you use a food thermometer so that you do not unnecessarily maintain high temperatures for longer than necessary for this first step.

The main benefits of heat treatment

– In the industry, this phase results in pasteurisation, which is useful for a significant reduction in the bacterial load. Pasteurisation is obtained either at 63°C for 30 minutes (Low temperature long time), or at 72°C for 15 seconds (High temperature short time); these values eliminate most of the pathogenic bacteria in vegetative form, yeasts and moulds; some enzymes are rendered inactive, while the taste of the milk undergoes almost no alteration; the whey proteins undergo little or no denaturation; and the bacteriostatic and cold agglutination properties remain practically intact(11).

However, we do not want to pasteurise milk that has already been pasteurised, but to modify its physical and chemical characteristics in order to obtain a dense yogurt like the one you see in the photo.

Therefore we have to do a high temperature long time pasteurisation, i.e. 20-30 minutes at 80-85 °C, or 5 minutes at 90-95°C. In this way, except for the spores, most of the micro-organisms in vegetative form are killed; most of the enzymes deactivated; almost all the whey proteins denatured. However, at such temperatures, some very sensitive people can detect a distinct ‘cooked’ taste, due to the formation of ketones and other volatile compounds ^{(12, 13)}.

– The denaturation of serum proteins such as β-lactoglobulin and α-lactoalbumin, which will initiate precipitation to form yogurt, also gives the characteristic white porcelain colour. Both serum proteins and caseins are found in milk in stable forms; so stable that they ‘feel no need to unite’ either with each other or with any other molecule present in the milk. But when the temperature exceeds 80 degrees, their (peptide) ligaments break down and if there is an optimum acidity in the environment (pH below 6.5) they become ‘available to new relationships‘. Thus, the participation of the serum proteins in the curd matrix through the new bonds built with the caseins allows coagulation with greater solidity and viscosity ⁽¹⁴⁾.

– Heat treatment allows the creation of a micro-aerophilic environment (at low oxygen levels); this point is fundamental, as many strains are weakly aerotolerant (e.g. lactobacillus), but grow best when there is little oxygen in the environment.

– Last but not least, it serves to increase the non-fat dry matter of the milk, which is consisting of lactose, protein and minerals, and so we get an optimally thick yogurt: nothing mysterious, boiling the milk inevitably reduces its water content through the well-known evaporation, and the end product becomes more concentrated.

According to the Turkish Codex Alimentarius (TSE), yogurt must have 12% low-fat dry residue. Although Turkish yogurt is not as dense as Greek yogurt (a characteristic that comes from being strained), it is still much denser than many yogurts present on the market. This recipe will help you make an excellent, homemade thick yogurt that is as good as and better than the store-bought ones.

2) First cooling

After the heat treatment, we need to cool the milk. This phase is used to bring the milk to a temperature just high enough to facilitate the growth of the lactic ferments; as these are living organisms with special needs, the ideal range for this to happen is between 43 and 45°C.

3) Preparation of the starter cultures

If you want to use a starter bought in a pharmacy, follow the instructions on the packet.
If, on the other hand, you prefer to start with a yogurt (homemade or store-bought), you must be sure that it is natural (not sweetened, not with fruit, etc.) and not very close to its expiry date (over time, the number of milk enzymes present will inevitably decrease).
Dissolve as much as you need (about 1-2% is a perfect proportion: I use 1 tablespoon of home-made yogurt for 1 litre of milk), together with a few tablespoons of milk at room temperature.

And now get ready for the most important stage of homemade thick yogurt, which makes even industrial factories shake in their boots: fermentation!

4) Fermentation

Fermentation is the decisive step in the whole process: important changes occur in lactose, milk proteins and microbial content; while no major changes occur in vitamins and minerals. The transformation of lactose into lactic acid not only gives the yogurt a slightly acidic taste, but also acts as a co-factor for several physical and chemical changes. These include coagulation of the milk, increased bio-preservation, as well as the digestibility and assimilability of milk proteins and sugars.
All of this is due to the perfect teamwork between L. bulgaricus and S. thermophilus, whose symbiotic actions promote increased acidification, and therefore more efficient fermentation, which would never be possible if the bacteria were used individually.
Optimum fermentation takes place between 43-45 degrees and should be completed in 4-5 hours.

5) Final cooling

Once the desired pH value (around 4.3-4.5) has been achieved during the fermentation phase, we can end it to inhibit the growth and metabolic reaction of our lactobacillus and finally stop the acidification of the product; this is achieved by moving the yogurt into the fridge (below 10 degrees, better 4 degrees). The yogurt should remain at these temperatures for a minimum of 12 hours in order to achieve perfect firmness.

HOMEMADE THICK YOGURT RECIPE

Ingredients

1 litre of pasteurised, semi-skimmed milk (better if organic): set aside 2 tablespoons to add to the starter (you can opt for full-fat milk but skimmed milk is not recommended)

1 level tablespoon of yogurt, homemade or store-bought (organic is better).

You will also need a well-washed steel pot and spoon, a sterilised container (or containers) for making the yoghurt and an oven!

Directions

Set aside 2 tablespoons of milk in a clean bowl and leave it at room temperature.
Put 1 tablespoon of yogurt (always use clean spoons) in another bowl to use as a starter.
Bring the milk to the boil (above 80 degrees), and keep it at this temperature for about 15-20 minutes, stirring frequently (if not continuously) so that it doesn’t stick to the bottom of the pot; if you can’t stir continuously, leave a spoon placed diagonally in the pot to prevent the milk from spilling out; Furthermore, choosing a pot that has a volume of at least 3 times the amount of milk will help prevent nasty accidents; if you think that the milk has stuck a bit, then once it has finished cooking, transfer it to another heat-resistant glass/ porcelain/ earthenware container.
Now you can let the milk cool down; to bring it to the optimum fermentation temperature (i.e. 43-45 degrees) you have two options:

1) put the pot (or the container you have chosen) inside a basin full of cold water;

2) wait for it to cool naturally (2 litres of milk takes about 25 minutes).

Extra tip

Obtaining and calculating these temperatures is very easy with a food thermometer; if you don’t have one, follow my tried and tested method.
Wash your little finger (considered the most thermo-sensitive one) very well and put it inside the hot milk (not boiling: do this test after about 10-15 minutes) and count up to 7-8 seconds; if you can hardly hold it, it means that the milk is ready to receive the starter, i.e. the starter cultures.
If you can’t keep your finger in it at all, it means that the milk is still too hot; wait a few more minutes for it to cool down and do the test again.
If, on the other hand, you can hold your finger in for much longer than 8 seconds, this means that the milk has cooled beyond the ideal temperature: warm it up a little more and repeat the test

While you are waiting, mix in a bowl the starter (the yogurt to be used to start the coagulation) with 2-3 spoons of milk that you have kept aside at room temperature; let the yogurt melt in a homogeneous way creating a sort of cream.
Now the moment of truth. But before combining the milk and the starter, we have to prepare the fermentation area: for a better control I recommend using the oven, either on or off – it is always very useful for the most complicated part of the whole process.

As it is insulated, it allows the initial heat to be maintained, so with the following steps you can ferment homemade thick yogurt without turning it on, extending the duration of fermentation to 7-8 hours:

– you can leave only its lamp on, it will help to maintain the temperature;
– if turning on the lamp also starts the ventilation, then insert a container full of boiling water to be renewed every two hours;
– otherwise, you can also cover the mixture of soy milk and starter with a kitchen cloth, then a blanket and leave for 7-8 hours.

To be sure 100% of the result, you have to turn on the oven: but at a temperature of about 43-45 degrees; in this case fermentation will take 4-5 hours.

Fermentation at these temperatures (with the oven on) takes between 4 and 5 hours.
Turn on the oven and while it reaches the desired temperature (it will only take a few minutes) you can mix the starter with the milk, stirring it gently; you can use a syringe to mix it homogeneously or with a spoon.

Here too you have two options

– use one container

– several containers (glass jars are preferable): in this case I suggest you combine the milk with the starter in the pot (or other) and then with a ladle transfer the future yoghurt into the containers.

Without wasting time and trying to be as stable as possible, transfer the container(s) into the oven and leave it/them there for 4-5 hours.
Then turn off the oven, let the semi-yogurt cool down to room temperature (other 2-3 hours). I call it semi yoghurt because it will only become real yogurt after the last step, the final cooling.
To do this, transfer the yogurt draft as gently as possible to the fridge, without any lid.
After a minimum of 12 hours (the longer it takes, the firmer it becomes) you will have a perfect homemade thick yogurt. Only then can you close the container(s) with the lid.

To make Greek yogurt or filtered yogurt, simply pour the yogurt thus created into a kitchen muslin and leave it to strain for 4-12 hours in the fridge. But severe penalties for those who think of throwing away the water that has formed: whey is very functional and useful. An article on how to use it in our kitchens is coming soon, but in the meantime you can use it to make bread or smoothies.

The homemade yogurt made with this recipe will keep for 15 days in the fridge: clearly a utopia, as it will ‘disappear’ much sooner.

Enjoy your creation and good revolution to all.

Bibliography
1) Gökçen DURUKOĞLU. AN ESSAY ON THE ETYMOLOGY OF THE LEXEME “YOGURT” Uluslararası Türk Lehçe Araştırmaları Dergisi (TÜRKLAD) Cilt 1 Sayı 1 2017. 100-103
ZZ Sfakianakis, P., & Tzia, C. (2014). Conventional and Innovative Processing of Milk for Yogurt Manufacture; Development of Texture and Flavor: A Review. Foods (Basel, Switzerland), 3(1), 176–193. https://doi.org/10.3390/foods3010176
2) Weerathilake, W. A. D. V., et al. “The evolution, processing, varieties and health benefits of yogurt.” International Journal of Scientific and Research Publications 4.4 (2014): 1-10.
3) Shah, Nagendra P. “Health benefits of yogurt and fermented milks.” Manufacturing yogurt and fermented milks 327 (2006).
4) Kok, Car Reen, and Robert Hutkins. “Yogurt and other fermented foods as sources of health-promoting bacteria.” Nutrition reviews 76.Supplement_1 (2018): 4-15.
5) El-Abbadi, Naglaa Hani, Maria Carlota Dao, and Simin Nikbin Meydani. “Yogurt: role in healthy and active aging.” The American journal of clinical nutrition 99.5 (2014): 1263S-1270S.
6) Hamann, W. T. and E. H. Marth. “Survival of Streptococcus thermophilus and Lactobacillus bulgaricus in Commercial and Experimental Yogurts.” Journal of food protection 47 10 (1984): 781-786 .
7) il Codex Alimentarius della FAO, www.codexalimentarius.org
8) Bourlioux P, Pochart P. Nutritional and health properties of yogurt. World Rev Nutr Diet. 1988;56:217-58. doi: 10.1159/000416229. PMID: 3142155.
9) Aurora Perez-Cornago, et al Intake of High-Fat Yogurt, but Not of Low-Fat Yogurt or Prebiotics, Is Related to Lower Risk of Depression in Women of the SUN Cohort Study, The Journal of Nutrition, Volume 146, Issue 9, September 2016, Pages 1731–1739
10) Ouuwehand, A. C. e Salminen, S., Isolauri, E. Probiotics: an overview of beneficial effects. 82, 2002, Antonie van Leeuwenhoek, p. 279-289
11) Chandan R.C. Chapter 1 History and consumption trends. In: Chandan R.C., editor. Manufacturing Yogurt and Fermented Milks. Blackwell Publishing; Ames, IA, USA: 2006. pp. 3–17.
12) Walstra P., Wouters J.T.M., Geurts T.J. Dairy Science and Technology. Taylor & Francis Group, LLC; Boca Raton, FL, USA: 2006. Chapter 7 Heat treatment; pp. 225–272
13) Boelrijk A.E.M., de Jong C., Smit G. Chapter 7 Flavour generation in dairy products. In: Smith G., editor. Dairy Processing. Woodhead Publishing LTD; Cambridge, UK: 2003. pp. 128–153.

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