Butter Science 101: Basic Lipid Chemistry and Butter Structure
Butter consumption continues to increase in the United States. Data from the USDA Economic Research Service shows that in 2019, U.S. citizens consumed 6.2 pounds per person – a more than 26% increase from 2010.
Butter, like many dairy products, is made from only a couple of ingredients. An Act of Congress that was approved March 4, 1923 defines butter as being “made exclusively from milk or cream or both, with or without common salt and with or without additional coloring matter and contains not less than 80% by weight of milkfat, all tolerances allowed for.” In addition to salted and unsalted butter, there are two main types of butter – sweet cream butter and cultured butter. The typical composition of butter is: 80-82% fat, 16-17.5% water, 1.5% salt, and 1% milk solids (vitamins, minerals, and lactose).
While butter is a simple product made from only a couple of ingredients, the physical changes that take place during butter production are more complex.
The most important aspect of buttermaking is cream quality. If you do not have quality cream, you can’t make quality butter. Some important measures for cream are milkfat content and pH. Milkfat content should be in the range of 35-40%. If this value is too high or too low, it will negatively impact yield efficiency. The cream should have pH of 6.4-6.7. If the pH of the cream is too low (below pH 6.4), it is indicative of the presence of undesired bacteria. Other important values to monitor include standard plate count, coliform count, etc.
Since buttermaking by its very nature has the goal of concentrating the fat in cream, the quality of the fat/lipid component of the starting cream is critical. Two main reactions that can occur to fat are lipid oxidation and hydrolytic rancidity. The former involves the reaction of fat with oxygen resulting in cardboard-like off flavors. The latter is usually due to the breakdown of triglycerides by lipases (enzymes that breakdown fats), resulting in baby vomit or soapy-like flavors. Therefore, quality metrics associated with these reactions should be included during cream testing (see table below).
The lipids or fat and types of fat in milk are important to understanding the science behind buttermaking. Triglycerides make up about 97-98% of the fat found in milk. The rest of the fat content in milk is divided up of mono & di-glycerides (about 0.5%), cholesterol (about 0.3%) and phospholipids (about 0.6%). The amounts and structure of these lipids serve important roles in the emulsification effects in buttermaking, which impact melting and spreadability.
The fat in milk is found in the form of milkfat globules, which range in size from 0.1-20 microns. Milkfat globules have three layers that protect fat triglycerides - these layers protect the quality of the fat. Excessive pumping or handling of milk can breakdown and damage the layers surrounding the milkfat globules. This introduces oxygen causing oxidization or allows enzymes to get into the globules causing off flavors to develop (hydrolytic rancidity). This is why it is important to preserve cream quality for buttermaking.
Lipolysis, or the breakdown of triglycerides with the release of fatty acids, produces flavors, which in the case of buttermaking, may not be desired. Intact triglycerides do not have much flavor or taste, but enzymes like lipases can break down triglycerides into free fatty acids, which are more volatile and interact with our olfactory glands to give strong flavors, which, again are not desired in buttermaking.
The fat in milk is about 70% saturated (solid at room temperature; single bonds in the fatty acid structure) and 30% unsaturated (liquid at room temperature; double bond(s) in the fatty acid structure). The structure of the fats in butter is very important as they will impact the melting and softness of the butter. As mentioned earlier, triglycerides are the predominant fat found in milk. Triglycerides have a “tuning fork” structure that allows them to nest and form stable structures, which allows the fat to remain solid at room temperature. However, if you introduce unsaturated fatty acids (double bonds) this will cause a kink in the chain and the triglycerides won’t nest together as nicely. This causes the structure to be more unstable and “fall apart” more easily. For example, they may become liquid at room temperature. As mentioned, this impacts the melting point and spreadability of the butter.
The more double bonds you have (unsaturated fatty acid), the lower the melting point and the more likely it will be liquid at room temperature.
Butter Processing Overview
Butter processing starts with processing milk in a milkfat separator to separate the cream from the skim milk. Cream is then pasteurized. The minimum time/temperature parameters for pasteurization are 30 minutes at 165°F or 15 seconds at 185°F. These are higher pasteurization temperatures than typically used for fluid milk processing or cheesemaking. These higher temperatures are necessary for cream pasteurization because cream is higher in total solids and the hotter temperatures are needed to ensure proper heat treatment. The higher pasteurization temperatures are also needed to inactivate certain enzymes like lipases, which can cause off flavors in butter made from raw cream.
Once the cream is pasteurized, it is cultured (if making a cultured butter) and then tempered. This step involves gently increasing the cream temperature over time and controls fat loss during the buttermaking process. After tempering, the cream is then ready for churning, working, salting (if applicable), packing, and chilling.
While sweet cream butter is the predominant butter type in the U.S., more consumers are looking for European-style high fat or cultured butter. Butter is cultured by adding bacteria, like Streptococcus cremoris, Streptococcus lactis sub diacetylactis and Lueconostoc to the cream. Similar to cheesemaking, by adding culture, the bacteria ferment or breakdown lactose and citric acid and form
end products like lactic acid and aroma compounds like diacetyl, which has a buttery aroma typically associated with microwave popcorn. The fermentation-produced lactic acid results in cultured butter typically having a pH around 4.4 to 5.0, while sweet cream butter usually has a pH similar to that of cream/milk (~6.0 to 6.7).
Tempering & Crystallization
After pasteurization (and culturing if applicable), the next step is tempering. During pasteurization, there will be liquid fat in the milkfat globules because the fat will be above its melting point. As the milkfat cools, some of the fat, beginning on the exterior of the fat globule, will become solid again. During this cooling step, the crystallization of the milkfat is impacted. In buttermaking it is very important to achieve the desired balance of solid (crystalized) milkfat and liquid milkfat. As the milkfat cools, you will get regions within the globules of crystalized milkfat and regions of liquid milkfat. This ratio of crystalized and liquid milkfat dictates how soft and spreadable the butter is going to be. The more solid or crystalized milkfat, the harder, less spreadable the butter will be. Cream temperature will increase as a result of giving up the latent heat of crystallization. For ideal churning with a minimal fat loss, the liquid fat must be on the exterior of the fat globule. During this migration, or inversion, temperature increases. It is important to note that this process takes time – ideally 18-24 hours. This is a simplified version of the chemistry involved. The take-home message is that the interplay between solid/liquid
fat in the milkfat globules has a tremendous impact on final butter texture and spreadability.
The next step in buttermaking is churning, which can occur in either a batch or continuous process. During churning, “phase inversion” is taking place. Cream is being transformed from an oil-in-water emulsion to butter, a water-in-oil emulsion. The cream is churned to encourage the fat globules to coalesce, aggregate, come together, and form solid butter granules/clumps. As this process continues, a more solid structure is formed made up of these butter granules, all the while buttermilk is being released and drained from the churn.
Working, Salting, Packaging, & Chilling
The final steps are working, salting, packaging, and chilling. Working the butter encourages the butter to form nice cohesive mass and further buttermilk removal. At this point, salt (if producing a salted butter) is worked into the butter as well. The final steps are packaging and chilling. There is a slow decrease in temperature as the butter is cooled. During cooling, the nuclei formed in the cream during tempering grow and may decrease spreadability. Chilling too rapidly can promote a short, brittle body and texture. Ideal spreadability develops somewhere in between.
Butter Short Courses
This was a quick look at some of the science behind buttermaking. If you want to learn more about buttermaking, CDR offers several short courses o butter: Buttermaking Fundamentals (online and in-person options), Buttermaking Comprehensive as well as a Buttermakers License Apprenticeship. For more information visit the CDR Short Courses webpage.
Note: This article first appeared in the Dairy Pipeline.