Pasteurization slows down bacterial proliferation in foods (usually liquids) by increasing and then reducing their temperature. Milk sold in stores must be pasteurized in a particular way to meet the safety requirements imposed by state regulations. Consuming unpasteurized milk carries a high risk of bacterial diseases and is particularly dangerous for young children, the elderly and all people with a weak immune system. If you milk your cows or goats, you can avoid the bacterial growth of the milk and extend its shelf life by learning how to pasteurize it at home.
Steps
Part 1 of 2: Preparation
Step 1. Prepare a water bath
Fill a large saucepan with about 8-10 cm of water; put a smaller pot inside, avoiding the base touching the bottom of the first. This method reduces the risk of burning the milk and giving it the classic bitter taste.
Step 2. Place a clean cooking thermometer inside the smaller pan
You have to constantly monitor the temperature, so a floating model (specific for milk) or the one for caramel with a hook are the best solutions. First wash the thermometer in very hot soapy water and rinse it thoroughly; it would be better to sanitize it by wiping it with disposable wipes moistened with alcohol and then rinsing it once more.
If the thermometer does not have a clip and is not floating, you must manually dip it into the milk frequently during pasteurization. Work near a sink to be able to clean and disinfect the meter after each measurement
Step 3. Prepare an ice bath
The faster you cool the milk after pasteurization, the safer and tastier it is. Fill the sink or large tub with cold water and ice, so it's ready right away.
- An old model of ice cream maker is perfect for this operation; fill the outer compartment with ice and rock salt, as you usually would.
- Read all the instructions described below before preparing the ice bath. You can then decide whether to use the long pasteurization process, in which case you have to leave the ice in the freezer for another half hour.
Part 2 of 2: Pasteurization
Step 1. Pour the raw milk into the smaller pot
If it has not been filtered after milking, pour it through a sieve.
For small quantities at home, it is easier to just pasteurize 4 liters of milk at a time
Step 2. Heat it while stirring it
Put the water bath on the stove over medium-high heat; stir frequently to evenly distribute the heat and avoid burning the milk.
Step 3. Monitor the temperature closely
Make sure that the thermometer probe does not come into contact with the walls or the bottom of the pan, otherwise the values are not true. As the temperature of the milk approaches the value listed below, stir constantly bringing the liquid from the bottom up to avoid forming areas that are warmer than others. There are two methods of pasteurization, both of which are effective:
High Temperature for Short Term (HTST)
Faster method that alters the taste and color less.
1. Bring the milk to 72 ° C.
2. Keep it at this (or higher) temperature for 15 seconds.
3. Remove it immediately from the heat source. Low Temperature for Extended Period (LTLT)
Recommended for the production of cheeses to avoid accidental overheating.
1. Bring the milk to 63 ° C.
2. Keep it at this or slightly higher temperature for 30 minutes. If the heat drops below 63 ° C, start calculating the time all over again.
3. Take it off the heat.
Step 4. Quickly cool the milk in the ice bath
The faster this phase is, the better the taste of the milk. Place the pan in ice water and stir frequently to dissipate the heat. After a few minutes, change some of the now lukewarm water with another cold one or with ice; change it every time it heats up: the higher the frequency, the better. The milk is ready when it reaches a temperature of 4.5 ° C. This process could take about 40 minutes in the water and ice bath or 20 minutes in the ice cream maker.
If it doesn't reach 4.5 ° C within 40 minutes, consider it contaminated; pasteurize it again and cool it faster
Step 5. Clean and sanitize a container
Before using it, wash it with very hot soapy water. For best results, take a heat-resistant container and, after washing it, sterilize it by immersing it in very hot water (at least 80 ° C) for 30-60 seconds.
Let it air dry; if you use a tea towel, you risk contaminating it with bacteria again
Step 6. Store the milk in the refrigerator
Pasteurization only kills 90-99% of the bacteria, so you need to refrigerate it to prevent the remaining colony from proliferating to dangerous levels. Seal the container and store it away from light.
If the process is done immediately after milking, simply pasteurized milk that does not undergo other treatments typically lasts 7-10 days. It spoils if it is stored at a temperature above 7 ° C, if new contaminants are introduced (for example by touching it with a dirty spoon) or if raw milk is not stored correctly before pasteurization
Step 7. Switch to specific tools
If you have livestock and need to pasteurize a lot of milk, consider buying a special machine, capable of pasteurizing large batches and preserving the flavor. LTLT (Long Term Low Temperature Technique) machines are cheaper and easier to use, but HTST (Short Run High Temperature Method) models are faster and typically alter the flavor of the milk less.
- However, the liquid must cool down quickly for the process to be effective; if the machine does not perform this step, remember to transfer it to an ice water bath.
- HTST models tend to denature few proteins, as the temperature does not exceed 78 ° C. This method allows to obtain constant results when the milk is used for the production of cheeses.
Advice
- After pasteurization, the liquid separates into milk and cream. The milk sold in some regions does not separate because it has undergone a treatment unrelated to pasteurization, called homogenization.
- If it takes too long to reach 4.5 ° C in the ice water bath, place it in the refrigerator once it has reached 26.5 ° C.
- Pasteurization does not alter most of the nutrients in milk, it may perhaps slightly reduce the concentration of vitamins K, B12 and thiamine. It has a strong impact on vitamin C, but milk itself doesn't contain much of it anyway.
- Calibrate the thermometer from time to time to make sure it's accurate. To do this, measure the boiling water in a saucepan. If you are at sea level, an accurate thermometer should indicate 100 ° C. If you get a different result, remember to subtract or add the detected difference to future measurements to get the real values.
- Dairies and companies that process milk often conduct alkaline phosphatase tests to make sure it has been pasteurized correctly.
- Since buffalo milk has a high fat content, you need to increase the pasteurization temperature by 3 ° C.
Warnings
- Don't let the thermometer touch the bottom of the pot, or you will get wrong readings.
- Infrared (non-direct contact) thermometers are not accurate for this job, because they only measure the surface temperature. If you plan to use one of this type, first bring some milk from the bottom to the top to get a more accurate result.
