The pH of milk can decrease due to several factors, primarily related to bacterial activity and the conversion of lactose into lactic acid. Understanding the key causes of this pH decrease is crucial for maintaining the quality and safety of milk and dairy products.
Bacterial Activity
One of the primary reasons for the pH of milk to decrease is the activity of lactic acid bacteria, such as those from the genera Lactococcus, Leuconostoc, Streptococcus, and Lactobacillus. These bacteria convert the lactose present in milk into lactic acid, which increases the acidity of the milk and lowers its pH.
Temperature
The temperature of milk can also play a significant role in the decrease of its pH. Higher temperatures can accelerate the growth and activity of these lactic acid bacteria, leading to a faster production of lactic acid and a subsequent drop in pH. For example, at 80°C and a pressure of 345 kPa, the pH of milk with 2400 ppm of CO2 can be decreased to as low as 5.63.
CO2 Concentration
The presence of carbon dioxide (CO2) in milk can also contribute to a decrease in pH. At high temperatures and pressures, CO2 can dissolve in milk, reducing its pH.
Starter Cultures
The intentional addition of starter cultures, which are acid-producing microorganisms, can also lower the pH of milk. These cultures are used in the production of various dairy products, such as cheese, yogurt, and sour cream, to create the desired acidity and flavor profiles.
Nutrient Deficiencies
Deficiencies in essential nutrients like cobalt, copper, or calcium can also contribute to a lower pH in milk, particularly in cow’s milk. These nutrient imbalances can affect the overall buffering capacity of the milk, making it more susceptible to pH changes.
Low Solids Content
Milk with a low solids content can also have a lower pH, as the concentration of lactose and other nutrients affects the rate of acid production by the lactic acid bacteria.
To maintain the desired pH range in milk, it is essential to control these factors. Proper refrigeration can slow bacterial growth, while the addition of specific nutrients can help maintain a healthy pH. In dairy production, the intentional use of starter cultures or acidulants can achieve the desired pH for various products.
Helpful pH Quantity to Consume
The normal pH range of milk is 6.6 to 6.9. Consuming milk within this range is generally considered safe and healthy.
How to Balance
- Store milk at proper refrigeration temperatures to slow bacterial growth.
- Ensure adequate nutrient levels in milk, particularly calcium, cobalt, and copper.
- Use starter cultures or acidulants intentionally to achieve the desired pH for specific dairy products.
History
The understanding of pH in milk dates back to the early days of dairy production. The use of starter cultures to control pH and create various dairy products has been a long-standing practice.
Contaminants, Chemicals, and Substances
- Lactic acid bacteria
- CO2
- Acidulants
- Starter cultures
- Nutrient deficiencies (cobalt, copper, calcium)
Solutions and Alternatives
- Proper refrigeration and storage
- Nutrient supplementation
- Use of specific starter cultures or acidulants
- Alternative dairy products with controlled pH levels
References
- https://www.sciencedirect.com/science/article/pii/S0022030203739897
- https://www.quora.com/Why-does-the-pH-of-milk-kept-at-room-temperature-become-lower
- https://www.dairyfoods.com/articles/82803-ingredient-feature-lowering-ph
- https://www.thoughtco.com/what-is-the-ph-of-milk-603652
- https://cheeseforum.org/index.php?topic=11487.0