Measuring Powdered Milk Replacers
Test results from scooping over 4,200 sample tablespoon measures of 100+ lots of 17 milk replacer products. These sample measurements indicated that scooping powder can result in significant variability between individual scoops, as high as 25+%, depending on the granularity, texture and compactibility of the specific milk powder product. Alternatively, weighing the powder removes that variability and improves the accuracy, insuring the desired amount of nutrients in the formula. If taking a little extra time to weigh the powder when measuring is not practical, some simplified measurement procedures are suggested that can help to lessen the degree of error introduced by choosing to scoop by volume.
How the directions on the package label specify to reconstitute the powder
The label instructions for PetAg®, Inc. milk replacers direct the user to “…shake 1 part powdered [product] into 2 parts warm water…”.
The Fox Valley Animal Nutrition, Inc. package label directs the user to “…shake 1 part powder into 2 parts of warm water.”
The labels for both products give further directions indicating that measuring by volume is the intent of the manufacturer. PetAg® includes a 1 tablespoon plastic scoop for this purpose. Fox Valley states “…mixing directions are based on volume, not weight, measures.” Neither label provides any volume/weight equivalencies, such as 1 Tablespoon of powder volume equals x.x grams of dry weight.
If the manufacturer’s specify simply scooping the dry powder, why would a user take the extra time and effort to actually weigh the powder prior to reconstituting with water? Does using weight rather than volume measures really make a significant difference?
How to determine which method is best for you
There are many instances where accuracy in measurement is a critical requirement when working with any powdered substance or product. From lab technicians to professional culinary instructors, all stress that weighing powder yields a superior measurement result over simply scooping by volume. For rehabilitators, it becomes a judgement decision on what level of accuracy is required when mixing milk replacer formula when working with young animals where their health and future are substantially affected.
WildAgain conducted the following tests with several powdered milk replacer products used by rehabilitators on assessing the degree to which differences in scooping versus weighing can be observed and measured.
In order to mix 1 part of powder to 2 parts of water by weight, the user needs to know the nominal weight of the ‘part’ of the powder, that corresponds to the weight of water for the same ‘part’.
A single, level (US) Tablespoon was used as the volume of the ‘part’ during the tests.
Each powdered milk replacer product was tested dry, as received from rehabilitator submissions (approx. 300 grams each), and labeled by product/lot number. Each product was individually scooped and weighed, for a total of 45 trial weights per product. Statistical evaluation on the results included calculating an average or mean value; high and low values; as well as a standard deviation, which is a measure of variability.
For test purposes, a single, level (US) Tablespoon was used as the volume of the ‘part’. Scientists have shown that 1 T of water weighs 14.8 grams (some people round the weight of a tablespoon of water to 15 grams for simplicity’s sake). The task was to determine the weights of 1 T of powder.
Observational as well as testing data showed variability between individual scooped volumes which can be influenced by several factors, including the following, and as discussed later:
1) Texture/Granularity of the powder
2) Cohesive characteristics
(influenced by 1 & 2 above)
4) Temperature of the powder
5) Individual user scooping method/technique
6) Scooping technique differences between users
Texture, Granularity and Cohesiveness of the powder
Observations indicated a continuum among the properties of the powders; simply stated as those that were more dry and free flowing to those that had a tendency to be more chunky and clumped together. As shown below, the Fox Valley products (left) exhibited the finer granularity, while the PetAg products were observed to bunch together (middle) and at times be much more chunky in texture (right).
Methods used by manufacturers for specific products, including spray drying methods used to produce a powder, can influence the cohesive characteristics and properties that can cause particles in the powder to become more sticky and clump together, such as the PetAg products shown above.
The scooping trials of the finer texture and the more free-flowing characteristics Fox Valley products produced a more consistent measurement as shown below with FV 32/40, with only slight percentage variations noted between individual scoops. Additionally, the average weights were consistent between the top, middle and bottom of the Fox Valley packages due to very low cohesiveness between dry powder particles.
When the same tests were performed on PetAg products, different results were observed. PetAg powders tend to result in about twice as much variability between individual scoops, compared to Fox Valley, since their powder is on the side of the continuum that is stickier, clumpy and less free-flowing.
Additionally, PetAg powders become noticeably more compacted as the user scoops from the top of the can or bag to the bottom. As shown below, a 28oz can of Esbilac® was opened and scooped top to bottom using a leveled, one tablespoon measure. The results showed that while the entire can had an average tablespoon dry weight of 6.0 grams per scoop, the top third of the can averaged a 5% lower weight of 5.7 grams (less compacted). By the time the bottom of the can was scooped, and had been repeatedly compacted, the average weight of a single tablespoon was 5% higher (at 6.3 grams) than the overall can average. That means, in this instance, that scoops from the top third of the can averaged a 10% lower weight than scoops from the bottom third of the can.
Shown another way below, the same data points from the Esbilac® can are plotted in the same order, from the top of the can to the bottom, but this time as a percentage variance from the can average scoop weight. It visually demonstrates how the percentage difference in scooped weight from the top half of the can when compared to the bottom half of the can totals almost 8%, or almost .5 gram per scoop.
The compaction of the powder in a can certainly has a significant influence on the variability in a single can. This can result in an even more pronounced effect between two different cans, as shown below with two cans of Esbilac. In this instance, it resulted in a 20% drop in scoop weight between finishing one can and then immediately starting a new can.
The statistics presented in the table at left provide a summary of the two measurement methods (scooping by volume and measuring by weight) for the two products specifically charted and graphed previously.
As shown, when scooping by volume, measurement variability is introduced and is as quantified below in terms of minimum/maximum scoop results (both in terms of weight in grams/TBSP as well as percentage variations from the can average scoop weight).
Another statistical measure of variability is also shown in the table, known as standard deviation, which is a measure of variability from an average value. It shows that the Esbilac® has twice the expected variability in the average (mean) value than the Fox Valley product tested.
Another graphical depiction of the standard deviation is shown below. This chart shows the results of scooping measurement error in 25 product/lots produced from each manufacturer. This involved measuring almost 2,200 tablespoon scoops. It confirms that the measurement variation in scooping the powder is twice as pronounced in the Pet Ag products when compared to the Fox Valley products.
Temperature of the powder at time of mixing
WildAgain conducted the measurement tests using powders at room temperature (70°F). However, a common practice is to store dry powder either in a refrigerator or a freezer, or sometimes both depending on short or long-term use requirements.
It stands to reason that since all of the powders tested had a tested moisture (water) content ranging from 4-6%,that powder stored at 0°F would likely contain ice crystals. If this occurs, those ice crystals could cause some of the dry powder particles to be frozen or bound together. This could cause some degree of clumping or stickiness in the powder that could impact scooping, such as creating small unseen voids in the scoop of powder.
While not impacting measurement, the rehydration process could be negatively impacted when the powder is introduced to warm water, as it would accelerate a decrease in water temperature. Taking 40°F powder from a refrigerator and adding it directly water would accelerate a decrease in water temperature, but to a lesser extent. Removing the powder from either a freezer or refrigerator ahead of the time to mix and allowed to attain a room temperature in the range of 70°F helps mitigate the predictable drop in water temperature.
The WildAgain measurement testing had a single person performing all of the scooping, while others monitored the measuring and recorded the weighed scoop results. These measurements were conducted in a controlled setting, with the focus on nothing other than attempting to obtain a consistent scoop weight over a series of 45 scoops per product/lot. These results were influenced by the manner and technique of the single person.
It seems improbable that any two people would scoop powder in the exact same manner. Some would likely have a slightly softer or heavier touch. Some would take more or less care in leveling off the top of the scoop. Others may stir the dry powder prior to scooping and some may scoop directly from the package or can, which could contain compacted powder. When multiple users are involved in this type of measurement process, variability is likely.
“Variations in measurement can have a significant effect on baked goods. To prove this point, we asked 10 home cook volunteers to measure out 1 cup of flour and 3 tablespoons of water. The weights of the measured flour and water varied by as much as 20 percent!”
(Excerpted from Weighing in on Weights and Measures, from The Complete America’s Test Kitchen Cookbook.)
Tools and information needed for weighing ingredients
Once a decision is made to weigh the ingredients, two key items are required.
First, a gram scale. For most applications, a scale with an accuracy to at least a tenth of a gram (e.g. 5.6 grams) is needed. Once very expensive, these devices can now be found inexpensively at a cost of only $10-20.
Many of the tests performed and described on this website utilized a pocket-sized scale with accuracy to one-hundredth of a gram (e.g. 5.69 grams) and handling a maximum weigh of 500 grams. The cost was under $15 at a popular online retailer. Make sure that the scale has a Tare function to zero the weight of the measuring vessel.
Second, standard weights of the ingredients (grams/tablespoon). The easiest one to obtain is the weight of water, at approximately 15 grams/tablespoon.
The dry weights of many of the powders and some other commonly used ingredients can be found as part of the WildAgain Wildlife Formula Calculator listed under the “TNA” tab of the speadsheet.
Suggestions to minimize measurement error when scooping powder
If weighing is simply not an option, here are some suggestions to minimize error when using volume measurements
Focus on the task at hand. Slow down and try to be as precise and consistent between scoops as possible.
Use a scooping measuring vessel (tablespoon, ½ cup, cup, etc.) with a smooth and level rim. Level off the amount of the powder with something flat, such as the back of a table knife.
When possible, have a single person perform the dry measures. When multiple users are required to accommodate shift schedules, for example, discuss protocols to be consistent and minimize differences between users.
To minimize the effects of compaction, consider rolling the can to redistribute the powder that may have settled during shipment, storage, or repeated scooping. If packaged in a bag, turn the bag over from top to bottom to accomplish the same redistribution.
Though not specifically tested, use room powder that has been allowed to attain room temperature. (store powder below 40°F.)
Scooping or weighing when measuring – which is correct, or better? Both actually, depending on the user’s objective. If time availability is short and accuracy may be less critical, measuring by volume may be acceptable. Measuring by weight takes a bit longer, but yields a more consistent and accurate result, especially in instances where a high accuracy is desired.
As shown below, the range of volume measurement error (lowest and highest data points) was observed as almost three times as great in the PetAg products when compared to the Fox Valley products. This appears to be due in large part to the texture, granularity and compaction described earlier. Yet even in the Fox Valley products, the error rate can be in the 3-5% range.
Lastly, remarkably the extremes of the observed measurement error most always was on the low side, 1.5 to 2 times the error on the high side. This is likely caused by small voids caused by clumpy or sticky powder. The unintentional result of this could be preparing a formula that is lighter in the powder and accompanying nutrients, and thus underfeeding an animal inadvertently.
See Mixing Guide for more suggestions.
The Complete America’s Test Kitchen Cookbook. The Editors at America’s Test Kitchen, 2017. Random House, Boston MA.
Mechtly, E. A: The International System of units, NASA-SP=7012, 1964, 1973. (The reference indicates the exact conversion to cubic metres is 14.78676478125 mL . One ml is as equivalent to 1 gram.)