Inadequate or incorrect coagulation of milk, cream, or combination either by Direct Acidification or primarily Lactic Acid or Rennet coagulation is often the first point at which cheese making signals that there is something wrong with the make. This article explores the common coagulation defects with descriptions and causes, sorted by root problem.
- Inadequate coagulation in specified time due to milk.
- Temperature of milk too low or high.
- Using same amount of rennet for different milk types, either 1% fat versus full fat, and between cow, goat, and sheep’s milk, and even between different cow or goat species.
- Low casein content of the milk.
- Old milk, during the time between milking and cheese making, bacteria can increase.
- Severity of heat treatment during pasteurization, Ultra Pasteurized milk is difficult to coagulate, UHT milk may not coagulate at all.
- Starter culture inhibition due to mastitic and late-lactation milk, higher free fatty acid levels, antibiotic residues.
- Low calcium level in milk, calcium levels reduce at end of lactation season. More common in pasteurized milk, the common solution is to add diluted Calcium Chloride.
- Inadequate coagulation in specified time due to starter culture providing improper pH of milk.
- Poor starter culture activity level due to age or improper storage will result in a lower schedule of pH drop. For acid coagulated cheeses this means a longer time to curd set. For rennet coagulated milk higher milk pH at time of renneting will also result in slower coagulation.
- Inadequate coagulation in specified time due to incorrect amount of rennet.
- Too little rennet can result in i) slow mostly acid coagulation rather than rennet coagulation, ii) very soft curd that will shatter when cut, and iii) poor flavor development during aging.
- Too much rennet can result in i) unusually rapid coagulation and an too firm rubbery curd that when cut will tear, ii) a curd that will retain too much whey, and iii) develop a bitter taste during aging.
- For these reasons, rennet amounts, either liquid, paste, posder or tablet, should be measured very accurately.
- Rennet strength is degraded due to improper storage or excessive age
- Inadequate coagulation in specified time due to poor dilution of rennet.
- Using warm chlorinated water for dilution before adding to milk, Chlorine is a strong oxidizing agent and rapidly destroys the rennet enzymes. Some people use bottled water to pre-dilute their rennet.
- Waiting too long between pre-diluting rennet in cool non-chlorinated water and adding it to milk, as rennet enzymes become unstable when diluted and loses strength.
- If using dry powdered or tablet rennet, waiting too short between pre-diluting in cool non-chlorinated water and adding it to milk such that dry rennet is not fully dissolved.
- Pre-dilute water is low alkalinity (above neutral 7.0 pH) resulting in inactivity of the rennet. Causes of low alkaline water are i) naturally alkaline water, ii) pre-dilution container having traces of detergent or sanitizer, iii) pre-dilution container was used for diluting colourants such as Annatto which can inactivate rennet.
- Incorrect stirring time of milk after adding pre-diluted rennet.
- Incorrect stirring method of milk after adding pre-diluted rennet.
Small Curd Particles
- Curd is made up of small-tiny curd particles.
- If milk curdled instantly into small particles when rennet was added, then acid level was far too high when rennet added. Reduce amount of starter or pre-ripening time before rennet is added or check if milk is sour before use.
- Stirring after curd has started to set, normally after few minutes if rennet coagulated curd.
- Milk was overheated.
- Inadequate coagulation in specified time.
- Movement of the milk during coagulation, for Acid Coagulated milk primarily when pH is 5.3 or lower.
- Stirring rennet in milk for longer than recommended time as breaks up curds as start to form.