question: Milk curdles when it comes into contact with strong acids, so does it curdle in your stomach?
comment: Yes it does. In fact, that is how cheese was first invented. Way, way back in time our ancestors used sheep or goat stomachs as a bladder to carry liquids in while they traveled (like a waterskin). Sometimes they would put milk in there and the rennet, which is used to make cheese and present in sheep/goat stomachs, would curdle the milk. Cheese is basically curdled milk so they stumbled on how to make cheese. Of course we have refined the process a lot since then.
passages: Milk contains dozens of other types of proteins beside caseins and including enzymes. These other proteins are more water-soluble than caseins and do not form larger structures. Because the proteins remain suspended in whey remaining when caseins coagulate into curds, they are collectively known as "whey proteins". Lactoglobulin is the most common whey protein by a large margin. The ratio of caseins to whey proteins varies greatly between species; for example, it is 82:18 in cows and around 32:68 in humans.
  
  Section::::Physical and chemical properties.:Salts, minerals, and vitamins.
   Milk-clotting proteases act on the soluble portion, κ-casein, thus originating an unstable micellar state that
  
  results in clot formation.
  
  Section::::Milk clotting.
   Milk coagulation is traditionally accomplished by coagulating enzymes extracted from sources such as rennet. In rennet, three chymosin isozymes hydrolyze κ-casein, a major protein fraction within milk, between Phe105 and Met106. Hydrophilic sub-regions of κ-casein are cleaved off, leaving behind largely hydrophobic aggregate. The enzymes thus destabilize κ-casein micelles and encourage clumping of hydrophobic protein residues, causing milk to curdle.
   Milk as a calcium source has been questioned in media, but scientific research is lacking to support the hypothesis of acidosis induced by milk. The hypothesis in question being that acidosis would lead to leaching of calcium storages in bones to neutralize pH levels (also known as acid-ash hypothesis).
  
  Research has found no link between metabolic acidosis and consumption of milk.
  
  Section::::Nutrition and health.:Milk and bone strength.
  
  A 2011 meta-analysis examining whether milk consumption might protect against hip fracture in middle-aged and older adults found no association between drinking milk and lower rates of fractures.
  
  Section::::Nutrition and health.:Lactose intolerance.
   For example, curd formation (rennet coagulation) is a reaction that occurs upon adding the enzyme rennin to milk. In this reaction, the substrate is a milk protein (e.g., casein) and the enzyme is rennin. The products are two polypeptides that have been formed by the cleavage of the larger peptide substrate. Another example is the chemical decomposition of hydrogen peroxide carried out by the enzyme catalase. As enzymes are catalysts, they are not changed by the reactions they carry out. The substrate(s), however, is/are converted to product(s). Here, hydrogen peroxide is converted to water and oxygen gas.
   In Indian English, used only in the Indian subcontinent, "curd" or "curds" instead refers to the traditional homemade yogurt (also known as dahi, while "paneer" and "Chhena" are used to denote curdled milk.
  
  Section::::Types of curd.
  
  There are two methods to make curd, with rennet and with acid. Using acid, like lemon juice, to make curd releases the lactose into the water. Thus the solid curd formed from this method is good for people with lactose intolerance. This type of curd is known as "Chhena" in India. 
   The amount of calcium from milk that is absorbed by the human body is disputed. Calcium from dairy products has a greater bioavailability than calcium from certain vegetables, such as spinach, that contain high levels of calcium-chelating agents, but a similar or lesser bioavailability than calcium from low-oxalate vegetables such as kale, broccoli, or other vegetables in the genus "Brassica".
   Curd is a dairy product obtained by coagulating milk in a process called curdling. The coagulation can be caused by adding rennet or any edible acidic substance such as lemon juice or vinegar, and then allowing it to coagulate. The increased acidity causes the milk proteins (casein) to tangle into solid masses, or "curds". Milk that has been left to sour (raw milk alone or pasteurized milk with added lactic acid bacteria) will also naturally produce curds, and sour milk cheeses are produced this way. Producing cheese curds is one of the first steps in cheesemaking; the curds are pressed and drained to varying amounts for different styles of cheese and different secondary agents (molds for blue cheeses, etc.) are introduced before the desired aging finishes the cheese. The remaining liquid, which contains only whey proteins, is the whey. In cow's milk, 90 percent of the proteins are caseins.
   Indian dairy products
  
  A variety of dairy products are indigenous to India and an important part of Indian cuisine. The majority of these products can be broadly classified into curdled products, like chhena, or non-curdled products, like khoa.
  
  Section::::Curdled dairy products.
  
  BULLET::::- Paneer is an unaged, acid-set, non-melting farmer cheese made by curdling heated milk with lemon juice or other non-rennet food acid, and then removing the whey and pressing the result into a dry unit.
   Other components found in raw cow's milk are living white blood cells, mammary gland cells, various bacteria, and a large number of active enzymes.
  
  Section::::Physical and chemical properties.:Appearance.
   Excess dietary fiber intake is a known cause of belching, gas and bloating. 
  
  Many vegetables are known to cause bloating due to high levels of fiber and undigestible sugars such as raffinose (e.g. beans, cabbage, broccoli).
  
  There are many individuals who are unable to tolerate dairy products because of lactose intolerance. Such foods should be eliminated from the diet if symptoms develop.
  
  Section::::Treatment.:Medications.
   The gastric chief cell (also known as a zymogenic cell or peptic cell) is a cell in the stomach that releases pepsinogen and chymosin. Pepsinogen is activated into the digestive enzyme pepsin when it comes in contact with acid produced by gastric parietal cells. This type of cell also secretes gastric lipase enzymes, which help digest triglycerides into free fatty acids and di- and mono-glycerides. There is also evidence that the gastric chief cell secretes leptin in response to the presence of food in the stomach. Leptin has been found in the pepsinogen granules of chief cells.
   After separation of potato juice the pulp is directed to the washing starch station, to isolate the starch. Most used are stream-oriented washers. In these machines pulp diluted with water is washed with a strong stream of water to flush out the milk starch. The mash smuggling with water is a waste product – dewatered potato pulp. Starch milk is contaminated by small fiber particles (potato tissue fragments) and the remaining components of the potato juice – that is why it is called raw starch milk.
  
  Section::::Potato starch production.:Starch milk raffination.
   The pH of milk ranges from 6.4 to 6.8 and it changes over time. Milk from other bovines and non-bovine mammals varies in composition, but has a similar pH.
  
  Section::::Physical and chemical properties.:Lipids.
   Like composition, fat globules vary in size from less than 0.2 to about 15 micrometers in diameter between different species. Diameter may also vary between animals within a species and at different times within a milking of a single animal. In unhomogenized cow's milk, the fat globules have an average diameter of two to four micrometers and with homogenization, average around 0.4 micrometers. The fat-soluble vitamins A, D, E, and K along with essential fatty acids such as linoleic and linolenic acid are found within the milk fat portion of the milk.
  
  Section::::Physical and chemical properties.:Proteins.
   Section::::Mechanisms for protein adsorption.:Biochemical.
  
  While the aggregates can explain much of the protein fouling found in milk processing, this does not account for it all. A third type of fouling has been discovered that is explained by the chemical interactions of the denatured β-lg proteins.
   Section::::Cheese and tofu.
  
  Milk and soy milk are curdled intentionally to make cheese and tofu by the addition of enzymes (typically rennet), acids (including lemon juice), or various salts (magnesium chloride, calcium chloride, or gypsum); the curds are then pressed.
  
  Section::::Egg sauces.
  
  In hot preparations emulsified with eggs like hollandaise and custard, curdling is the undesirable result of overheating the sauce. Sauces which contain starch curdle with more difficulty.
  
  In cold sauces like mayonnaise as well as in hot sauces, too large a ratio of fat to egg may also cause curdling.
  
  Section::::Milk sauces.
   Lactic acid is found primarily in sour milk products, such as koumiss, laban, yogurt, kefir, and some cottage cheeses. The casein in fermented milk is coagulated (curdled) by lactic acid. Lactic acid is also responsible for the sour flavor of sourdough bread.
   A side effect of the heating of pasteurization is that some vitamin and mineral content is lost. Soluble calcium and phosphorus decrease by 5%, thiamin and vitamin B12 by 10%, and vitamin C by 20%. Because losses are small in comparison to the large amount of the two B-vitamins present, milk continues to provide significant amounts of thiamin and vitamin B12. The loss of vitamin C is not nutritionally significant, as milk is not an important dietary source of vitamin C.
  
  Section::::Processing.:Pasteurization.:Filtration.
   Nutrition intake between whole milk drinkers and skimmed or low fat drinkers is different. An analysis of a survey done by the U. S. Department of Agriculture showed that consumers of reduced or low fat milk had greater intake of vitamins, minerals, and dietary fiber compared to the group of whole milk drinkers, yet zinc, vitamin E, and calcium were all under consumed in each group. The conclusion was that the whole milk drinkers were more likely to choose foods that were less micronutrient-dense, which resulted in their less healthful diets.
   Cheese consists of proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. It is produced by coagulation that is caused by destabilization of the casein micelle, which begins the processes of fractionation and selective concentration. Typically, the milk is acidified and then coagulated by the addition of rennet, containing a proteolytic enzyme known as rennin; traditionally obtained from the stomachs of calves, but currently produced more often from genetically modified microorganisms. The solids are then separated and pressed into final form.
   Some fresh cheeses are curdled only by acidity, but most cheeses also use rennet. Rennet sets the cheese into a strong and rubbery gel compared to the fragile curds produced by acidic coagulation alone. It also allows curdling at a lower acidity—important because flavor-making bacteria are inhibited in high-acidity environments. In general, softer, smaller, fresher cheeses are curdled with a greater proportion of acid to rennet than harder, larger, longer-aged varieties.
   One of the main actions of rennet is its protease chymosin cleaving the kappa casein chain. Casein is the main protein of milk. Cleavage causes casein to stick to other cleaved casein molecules and form a network. It can cluster better in the presence of calcium and phosphate, which is why it is occasionally added in cheese making especially from calcium phosphate-poor goat milk. The solid truncated casein protein network traps other components of milk like fats and minerals to create cheese. In digestion it is followed by other proteases cutting casein further to ultimately release and absorb the component amino acids and minerals. In a nutshell, curdling is chymosin cleaving casein, a process that is part of natural digestion and cheese making.
   Casein is the predominant phosphoprotein found in fresh milk. It has a very wide range of uses from being a filler for human foods, such as in ice cream, to the manufacture of products such as fabric, adhesives, and plastics.
  
  Section::::Industrial processing.:Cheese.
   Deep-frozen stomachs are milled and put into an enzyme-extracting solution. The crude rennet extract is then activated by adding acid; the enzymes in the stomach are produced in an inactive form and are activated by the stomach acid. The acid is then neutralized and the rennet extract is filtered in several stages and concentrated until reaching a typical potency of about 1:15,000; meaning 1 g of extract can coagulate 15 kg of milk.
  
  One kg of rennet extract has about 0.7 g of active enzymes – the rest is water and salt and sometimes sodium benzoate (E211),
  