What is the purpose of storage of milk?

It is essential to properly store your expressed/pumped milk to maximize its nutritional, immunological and antioxidant qualities. Human milk has anti-bacterial properties that help it to stay fresh and when stored per recommendations, human milk can maintain many of its nutritional qualities making it safe for use. Over time nutrients may break down in expressed milk lowering the quality and as such, it is important to try to give your baby the freshest expressed milk possible to ensure its rich quality.

Prior to expressing and storing milk you should:

• Wash your hands
• Use containers that have been washed in hot, soapy water, rinsed and air dried

Milk Storage Guidelines

This information is based on current research and applies to those who have healthy, full-term babies. Families with babies who are preterm/ in NICU/or ill should use more conservative guidelines.

General storage tips:

• All milk should be dated before storing. Use the first in, first out rule and use the oldest milk first
• Storing milk in 2-4 ounce (60 to 120 ml) amounts may reduce waste
• Refrigerated milk has less fat loss and more anti-bacterial and protective properties than frozen milk
• When combining milk expressed from different pumping sessions, ensure fresh milk is chilled in the refrigerator before adding it to previously expressed milk

Preferably, human milk should be refrigerated or chilled right after it is expressed. Acceptable guidelines for storing human milk are as follows.

Storage Containers

Bottles

• glass or hard-sided plastic containers with well-fitting tops
• avoid containers made with the chemical bisphenol A (BPA), identified with a number 3 or 7 in the recycling symbol. A safe alternative is polypropylene, which is soft, semi-cloudy, and has the number 5 recycling symbol and/or the letters PP. You can avoid the risks of plastic completely by using glass.
• containers which have been washed in hot, soapy, water, rinsed well, and allowed to air-dry before use or washed and dried in a dishwasher
• containers should not be filled to the top – leave an inch of space to allow the milk to expand as it freezes

Bags

• freezer milk bags that are designed for storing human milk
• squeeze out the air at the top before sealing, and allow about an inch for the milk to expand when frozen
• stand/lay the bags in another container at the back of the refrigerator shelf or in the back of freezer where the temperature will remain the most consistently cold

Disposable bottle liners or plastic bags are not recommended. With these, the risk of contamination is greater. Bags are less durable and tend to leak, and some types of plastic may destroy nutrients in milk.

Reheating Human Milk

Thawing From Frozen

• Thaw in the refrigerator overnight
• Run warm water over the sealed frozen container of milk
• Place frozen container in cup of warm water
• Use waterless warmer

Avoid boiling and microwaving as these methods will cause loss of nutritional properties of human milk and could unevenly hot making it dangerous for infants to drink (ABM, 2017).

Warming Refrigerated Milk

While many infants may be content drinking room temperature milk, some may have a preference for warmer milk. It is recommended to warm milk slowly in lukewarm water to protect fat content and nutrients

Common Questions

Why does my milk smell or taste soapy?

Sometimes thawed milk may smell or taste soapy. This is due to an enzyme in milk known as lipase (Newman & Pitman, 2014). The milk is safe and most babies will still drink it. If there is a rancid smell from high lipase when the milk has been chilled or frozen, the milk can be heated to scalding (bubbles around the edges, not boiling) after expression, then quickly cooled and frozen. This deactivates the lipase enzyme. Scalded milk is still a healthier choice than commercial infant formula.

Why is my milk separating?

Human milk naturally separates into a milk layer and a cream top when it is stored. This is normal. It is safe to shake or swirl the milk to combine the cream prior to feeding.

Is it safe to refreeze my milk after thawing?

Previously frozen milk that has been thawed can be kept in the refrigerator for up to 24 hours (Lawrence & Lawrence, 2010). There is currently limited research that supports the safety of refreezing human milk as this may introduce further breakdown of nutrients and increases the risk of bacterial growth. At this time, the accepted practice is not to refreeze thawed milk.

Can I reuse previously fed milk if my baby does not finish?

If baby does not finish the bottle during a feed, the recommendation is milk may be reused within 1-2 hours and after this time frame should be discarded to avoid transfer of bacteria from baby’s mouth to bottle (ABM, 2017). Many moms find storing milk in smaller quantities can help reduce waste if baby does not finish the bottle.

Is it safe to store my milk in a shared refrigerator?

Expressed milk can be kept in a common refrigerator at the workplace or in a day care center. The US Centers for Disease Control and the US Occupational Safety and Health Administration agree that human milk is not among the body fluids that require special handling or storage in a separate container (CDC, 2015).

I have thrush; is my milk safe?  

If you or your baby has a thrush or yeast/fungus infection, continue to breastfeed during the outbreak and treatment. While being treated, you can continue to express your milk and give it to your baby. Label any milk stored while you or baby is undergoing treatment. Be aware that refrigerating or freezing milk does not kill yeast. The safest, most conservative option is to discard pumped milk during thrush treatment. Some research shows using frozen milk pumped during thrush treatment should not pose any risk to healthy babies especially if the milk is boiled prior to use (Morbacher, 2010; Newman & Pitman, 2014). Read our post on thrush.

References

Academy of Breastfeeding Medicine. (2017) Clinical Protocol Number #8: Human Milk Storage Information for Home Use for Healthy Full Term Infants.  Breastfeeding Medicine, 12(7), 390-395.

Centers for Disease Control and Prevention (CDC). (2015). Breastfeeding: Frequently Asked Questions. Retrieved from https://www.cdc.gov/breastfeeding/faq/index.htm

Centers for Disease Control and Prevention (CDC). (2017). Proper Handling and Storage of Human Milk. Retrieved from https://www.cdc.gov/breastfeeding/recommendations/handling_breastmilk.htm

Lawrence, R.A. & Lawrence, R.M. (2010). Breastfeeding: A Guide for the Medical Profession (7th ed.). Elsevier Mosby, Philadelphia

Mohrbacher, N. (2010). Breastfeeding Answers Made Simple. Texas: Hale Publishing.

Newman, J. & Pitman, T. (2014). Dr. Jack Newman’s Guide to Breastfeeding, Revised Edition. UK: Pinter & Martin, Ltd.

Module 6. Common dairy operations

Lesson 17

CHILLING AND STORAGE OF MILK

17.1 Introduction

The first operation in a dairy plant is reception, chilling and storage of milk. Raw milk is pumped from the dump tank to the storage tank through a filter and chiller. The purpose of storage tank is to hold milk at low temperature so as to maintain continuity in milk processing operations and prevent any deterioration in quality during holding and processing period.

The milk may arrive at a chilling center or dairy plant in cans. After unloading the cans, milk is chilled and stored in storage tanks. Storage tanks are used to store raw or even pasteurized milk. Milk may be held in chilled condition (< 5°C) in the tank for up to 72 hours between reception and processing. Normally the milk storage capacity should be equivalent to one day’s intake.

17.2 Objectives of Storage Tanks

• To maintain milk at a low temperature so as to prevent any deterioration in quality prior to processing/product manufacture.

• To facilitate bulking of raw milk supply, which will ensure uniform composition

• To allow for uninterrupted operation during processing and packaging

• To facilitate standardization of the milk

17.3 Storage Tank

Storage tanks enable milk to be stored for longer period of holding. They must be designed for easy cleaning and sanitization, preferably through CIP process. Storage tanks consist of a stainless steel inner shell, a layer of insulation, an outer jacket and necessary fittings for inspection control and cleaning. The tanks should be insulated or refrigerated so that they can maintain the required temperature throughout the holding period. Glass wool, Thermocol, Corkboard, Foam glass or Styrofoam can be used for insulation. Corkboard or foam glass is used in the lower portions of the tank where the insulations may carry a part of the load. Agitation must be adequate for homogeneous mixing, but gentle enough to prevent churning and incorporation of air. In many storage tanks, chilled water circulation system is provided to maintain the temperature of milk. All closed type of tanks must be equipped with a manhole round (diameter ~ 450 mm) or oval shaped to permit access to the interior for cleaning and inspection.

For foam-free entry of milk, a curved filling pipe, which guides the milk towards the wall is used. It is better to fill the tank from below, i.e., by the lowest outlet pipe. The storage tanks containing raw chilled milk or standardized pasteurized milk are usually located on the first floor. This allows feeding to the milk pasteurizers or even gravity filling of milk. Now-a-days, big sized silos, usually of > 1.0 lakh litres capacity are installed in the dairies on the ground floor only. They are very useful in storing skim milk for feeding to the powder plants. In the dairy industry, rectangular tanks are less preferred as compared to cylindrical tanks, because cleaning of sharp corners (in rectangular ones) is difficult. Secondly, the agitation effect does not reach the extreme corners of rectangular tanks.

17.4 Types of Storage Tank

Storage tanks can be classified on the basis of their shape and other features.

17.4.1 Insulated storage tanks

These tanks merely stores the milk at a temperature at which it is filled. In most cases, depending upon the quality of insulating material, there is tendency of rise in the temperature of milk with long storage. These tanks are made up of a stainless steel inner shell, a layer of insulation (thermocol and glass wool) and an outer jacket of stainless steel or mild steel ( Fig.17.1, 17.2)

17.4.2 Refrigerated tanks

It has built-in refrigerating facilities so that stored milk is chilled as and when required. This additional feature of maintaining the desired temperature is an added advantage in these tanks. In refrigerated tanks, the hollow space between the inner and outer shells is used for circulating the cooling medium (chilled water or brine solution).

Fig. 17.1 Horizontal milk storage tank

Fig. 17.2 Vertical milk storage tank

17.4.3 Horizontal or vertical tanks

Horizontal tanks require more floor space than vertical ones, but need less headspace. For handling small volumes, horizontal tanks (5,000 to 15,000 litre capacity) may be used. Now-a-days, milk is stored in vertical storage tanks of one lakh litre capacity or more, commonly known as silos. These are vertical cylindrical tanks, installed outside the building. In these silos, milk feeding is from same discharge valve installed near the bottom (Fig 17.3).

Fig. 17.3 Sectional elevation of insulated milk silo

17.5 Chilling Equipments

17.5.1 Surface cooler

It can be either an individual unit or cabinet type. The latter consists of two or more individual units, compactly assembled and enclosed in a cabinet. It is usually larger than those used on the farm/chilling centre.

17.5.2 Plate chiller

It is widely used for large scale cooling of milk of 5000 to 60,000 lit./day at the chilling centers. They are efficient, compact and easily cleanable. In chiller the gasket plates are tightly held between the plates. These plates are so arranged that milk flows on one side of plate and cooling medium (usually chilled water) on the other. There is a counter current flow between the milk and the chilled water through alternate plates. It helps in efficient transfer of heat to the cooling medium resulting in quick chilling of milk. The chilled milk flows from the plate cooler to the insulated storage tank at 4°C. A mechanical refrigeration system (IBT) is needed.

17.5.3 Internal tubular cooler

It is a continuous cooling system consisting of a stainless steel tube about 2.5 – 5.0 cm in diameter surrounded by a similar tube, forming a concentric cylinder. Several such tubes may then be connected in series to obtain sufficient cooling. The cooling medium flows counter current to the milk flow.

17.5.4 Vat/tank cooling

It is suitable for batch cooling, especially of small quantity. It consists of a tank within the tank, with the space between the two being used for circulation of the cooling medium, by either pump or main pressure. An agitator is provided to agitate the milk for rapid cooling.