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Lumpy, ropy, sloppy, and viscous texture when making yogurt and kefir at home and how to fix that

Lumpy, ropy, sloppy, and viscous texture
Lumpy, ropy, sloppy, and viscous texture

Slow fermentation sometimes delivers a lumpy, ropy, sloppy, and viscous texture when making homemade yogurt and homemade kefir. Although it is easy to shake or stir those batches (as some even prefer the texture creamy) and make them drinkable or suitable for smoothies and granola bowls in the morning, many prefer getting their yogurt or kefir thick.

People wonder what the reason can be, and although it is clear that there was an inhibitor of the fermentation, the inhibitors are various. So we need to consider all and do the only one thing that could fix them all(read to the end)

Growth and acid production by starter cultures may be inhibited by bacterial viruses (bacteriophages) or added substances, including antibiotics, sterilant and detergent residues, or free fatty acids produced by or as a result of the growth of microorganisms, and natural (often called) indigenous antimicrobial proteins.

1. Antibiotic residue in the milk—Despite legislation and financial penalties, evidence suggests that residues occasionally still cause problems. A survey of the causes of slow acid production by cheese starters (the same for all starter cultures) in the UK (Boyle and Mullan, 2000, unpublished results) found that some 28 % of respondents attributed slow acid problems to antibiotics.

One reason is that tests for antibiotics are inclined to a specific antibiotic and do not capture other different antibiotics that may be present. Another reason is that a low level of different antibiotics synergistically slows down the acidification.

Antibiotics, on the other hand, are also naturally produced during fermentation. Raw milk contains lactococci. If favourable conditions for growth occur, then high numbers will result. Some Lc. lactis strains(found in Kefir) produce the antibiotic nisin. Nisin is a broad-spectrum antibiotic, and if produced, it will inhibit other starter cultures in the blend.

Providing adequate control of temperature during the production, storage, and distribution of milk nisin production should not be a problem for commercial manufacturers; however, it can be a significant issue for homemakers as the conditions they can support are rarely that strict or adaptable to changes.

2. Sterilant and detergent residues in the milk. Sterilant and detergent residues may inhibit the growth of starter bacteria. The minimum concentration required for inhibition varies with the different anti-microbial agents and between different strains of starter bacteria. Residues gain entry to milk at the farm, during transport to the factory, and the factory due to careless use of sterilant or detergents, incomplete draining, or inadequate rinsing of equipment.

In general, the concentration of these compounds in properly produced milk should not inhibit starters as there will be variations in every single batch of milk processed even when, in the end, it is filled in the same brand bottle/pack.

However, the situation with quaternary ammonium compounds (an antimicrobial agent contained in detergents and sterilizers) is unclear. These compounds are stable in milk and can be difficult to rinse off surfaces.

Nevertheless, quality assurance staff in some plants has ascribed some instances of slow acid production to sterilant and detergent residues. Boyle and Mullan (2000) found that some 17 % of cheese factories attributed acid production problems to these residues.

Frequently, homemakers are unable to check their use of detergents. However, rinsing utensils and containers with hot water immediately before use can help when making it at home.

3. Free fatty acids—Free fatty acids are present at low concentrations in freshly drawn milk. Their concentration may increase due to the activity of milk lipase or microbially produced lipases. Pseudomonas sps. (a type of germ), if permitted to grow in refrigerated milk, will produce lipases and high concentrations of free fatty acids.

Fatty acids are inhibitory to lactococci and, in particular, to Lc. lactis subsp. cremoris. (present in our Kefir starter) However, relatively high levels of fatty acids are required; 0.1% butyric, decanoic, hexanoic, and oleic acid were required to inhibit Lc. lactis subsp. cremoris. Such high concentrations of free fatty acids do not normally occur in modern hygienically produced milk held at correct storage temperatures.

However, homemakers do not have a way to test it before use, and although not common, it can be an inhibitor when making it at home.

4. Natural indigenous antimicrobial proteins - The ability of raw milk to inhibit the growth of many bacterial species has been known for centuries, and one of the earliest reports was authored by Hesse in 1894. Jones and his co-workers around 1920 termed the heat-labile inhibitors in milk as ‘lactenins’. The early work has been comprehensively reviewed by Reiter and MØller-Madsen (1963), and their paper in the Journal of Dairy Research is recommended reading. Recent work has shown that these inhibitors include:

- The lactoperoxidase-thiocyanate-hydrogen peroxide (LP) system

- Immunoglobulins

- Lysozyme

- Lactoferrin

- Vitamin binding proteins.

The most common effect that occurs when making it at home is agglutination (glue-like, viscous texture) due to the immunoglobulins. It has been known for many years that certain bacteria, including lactococci, agglutinate in raw milk. Agglutination is caused by relatively specific antibodies that occur in the globulin protein fraction in milk serum, particularly in the euglobulin and pseudoglobulin fractions. These antibodies, which generally originate from the cow's blood, are always present in milk but occur at high concentrations in the colostrum.

Agglutinins inhibit acid production in raw and pasteurized whole or skim milk. There is evidence of two types of antibody response.

Response One is where sensitive bacteria are attached to fat globules, and the second is where antibodies in the skim fraction cause bacteria to ‘stick’ together and form clumps and sediment to the bottom. In raw or pasteurized whole milk, the immunoglobulins inhibit acid production by facilitating the removal of sensitive bacteria to the cream layer and/or causing sensitive strains to agglutinate, form clumps, and sediment to the bottom of the container. Inhibition may also occur with some strains in skim milk. In this medium, the agglutinins cause sensitive strains to form clumps that settle on the bottom of the container and localize acid production.

Agglutinins are inactivated by heat treatment or homogenization, unlike lactoperoxidase, sometimes known as Lactenin L2, which survives a heat treatment of 71°C for 20 minutes; this treatment inactivates immunoglobulins. HTST pasteurization (72°C - 15s) partly inactivates the immunoglobulins; 50-75% of the agglutinating activity is destroyed by this heat treatment. Sterilized milk or bulk starter milk does not contain active agglutinins; the heat treatment has denatured the agglutinins.

So to solve the problem with lumpy, sloppy, or ropy texture, you need to remove other bacteria and bacteriophages, detergents, and antibiotic residue (and other ingredients), as well as suppress some agglutinins and this can be done at home if you follow the steps below:

- Get the cheapest milk in the shop. It is usually minimally processed to reduce the fat to the required 3.5%, has the lowest shelf-life expectations, and contains fewer additional ingredients.

- Rinse the containers and utensils well before use. Better fill the containers with hot water just before use for a few minutes to make sure that all detergent residue is diluted at maximum.

- Boil the milk and cool it down. Microwaves (when a flat container is used) can do it just great for 30 minutes at high power to prevent agglutination. In a microwave, the milk cannot burn, and at the same time, agglutinins will be denatured. Also, boiling changes the fats in milk, too. Milk contains short-, medium-, and long-chain fatty acids. While the total fat content is stable with boiling, some of the long-chain fats may be converted into short- and medium-chain fats, which would aid the entire fermentation process.

As you can see, the methods are not different from what our grandparents used.

Clarification: This article is focused on the quality of milk, which the bacterial cultures need to form a desired thick texture and frequent inhibitors. However, other ingredients added during production, like inulin, pectin, and corn starch, could sometimes deliver a grainy texture.

Non-fat kind of milk delivers a creamy or sometimes viscous to liquid texture due to the different combinations of essential nutrients.


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