Introduction
Butter is a dairy product composed of up to 80% butterfat as well as milk proteins and water. Butterfat is a mixture of triglyceride, an ester derived from glycerol and fatty acids which vary in different types of triglycerides. Butter can become rancid when oxidation occurs and breaks the triglyceride chains into smaller compounds, such as butyric acid and diacetyl. Proper packaging and storage are vital to prevent oxidation of butter. Other ingredients which are sometimes added include salt, various flavorings, and preservatives. Butterfat can also be known as milk fat and is defined as the fatty portion of milk. It is made by churning fresh or fermented cream or milk to separate the butterfat from the buttermilk. Although mostly made from cow milk, other types of milk can be used, such as sheep, goat, and buffalo. Butter remains solid when refrigerated, turns soft and spreadable at room temperature, and typically melts to liquid around 90°F. It has a variety of uses, such as a spread on bread products, a condiment on cooked vegetables, a dipping sauce for bread and some types of seafood, and cooking uses like pan-frying and baking. Butter is typically light yellow in color but can vary depending on the source animal and food coloring can be used to modify color as well. Butter can be both cultured and non-cultured. If cultured butter is desired, bacteria are added to create lactic acid from sugars in the milk by fermentation. Cultured butter is typically not washed or salted.
Butter Manufacturing
The origin of butter goes back about 10,000 years to when humans first began to domesticate animals. Most butters were made by hand on farms until the middle of the 19th century when the first butter factories began to appear. Today’s butter manufacturing is usually done as a continuous process, but batch processing is done on a smaller scale as well. The first step is procuring and preparing the cream, which can be provided directly by the milk dairy or separated from whole milk by the butter manufacturer. Sweet cream at a pH above 6.6 without rancidity or oxidation is preferable. If separation is required, the whole milk is pasteurized and passed through a separator. After cooling, the cream is stored and fat content is adjusted to the proper level, if necessary. Leftover skim milk is pasteurized, cooled, and stored for concentration and drying. The cream is pasteurized at a minimum temperature of 95°C to destroy enzymes and microorganisms. Mixed cultures are added to the cooled cream at this stage if fermentation is desired. pH will drop to 5.5 at 21°C and 4.6 at 13°C and most flavor development related to ripening occurs in between these two pH levels.
Whether cultured or non-cultured, the cream is then moved to an aging tank and subjected to controlled cooling to give the fat the required crystalline structure. The exact aging process can vary and is modified based on factors like the composition of the butterfat in terms of iodine value, which is a measure of unsaturated fat content. Butter contains fat in three separate forms: free butterfat, butterfat crystals, and undamaged fat globules. The proportion of these forms affects the consistency and hardness of the butter. More crystals will result in harder butter than those dominated by free fats. Typical aging length is twelve to fifteen hours. Once aging is complete, the cream is pumped to the churn (or continuous butter maker in a continuous process) through a plate heat exchanger which brings it to the desired temperature. This temperature is normally around 55°F although it can vary from 50°F to 62°F depending on conditions. If the temperature is too high, the butter will be made in a very short time but there will be a substantial loss of fat in the buttermilk. If the temperature is too low, churning will take a long time and the butter produced will be excessively hard. During churning, the cream is violently agitated to break down the fat globules, which causes the fat to coagulate into butter grains. As coagulation occurs, the fat content of the buttermilk liquid decreases.
After the cream is split into butter grains and buttermilk, the buttermilk is drained off. In traditional batch churning, the buttermilk is drained off when the grains reach a certain size. If a continuous butter maker is used, the draining is continuous during the churning process. Additional washing can occur at this stage to remove residual buttermilk and milk solids. The grains are pressed and kneaded together, consolidating the butter into a solid mass and breaking up embedded pockets of buttermilk and water into small droplets. This liquid phase is drained off and if added, the butter is ready for salting at this point. Salt improves flavor and acts as a preservative. In batch production, salt is spread over the surface in an amount of 1% to 3% of the total butter weight. In continuous production, a salt slurry at a concentration of 10% is added. It is important to work the butter and salt vigorously to ensure a homogenous blend of butter granules, salt, and water. The fat moves from globule to free fat during working. Water droplets will decrease in size and should not be visible after the working Is complete. Some water can be added to standardize the moisture content. Proper working is essential to obtain maximum yield and get the desired characterization of aroma, taste, shelf-life, appearance, and color. After working is complete, the finished butter is discharged, packaged, and moved to cold storage.
Conclusion
NIR spectroscopy has emerged as a tool for rapid, non-invasive, and cost-effective analysis of parameters of interest in butter that could potentially replace traditional reference methods. As is the case with all dairy products, fat content is of paramount importance at all stages of the butter manufacturing process, from the initial stage of cream measurement all the way to the final working (and salting in the case of salted butter). Solid Fat Content (SFC) is of particular importance during the aging stage as optimized crystallization conditions are crucial for product quality. The fat analysis involves time-consuming and expensive wet chemistry methods and in the case of SFC, NMR spectroscopy is used which requires a sixteen-hour delay before tempering of the sample to meet approved reference standards. Moisture is also important, and water is known as one of the most detectable compounds using NIR spectroscopy due to its high absorbance of NIR light. Although salt does not directly absorb NIR light, it does change other compounds that absorb in the NIR spectrum and the feasibility of this indirect measurement has been proven in studies. As is the case with most food products, there are different grades and quality levels in butter that make it a target for adulteration. Misrepresentation of a region of origin or animal of milk source is two potential methods of butter adulteration. Another is adding a less valuable product to butter. One such potential adulterant for butter is tallow, a hard-fatty substance made from rendered animal fat. NIR spectroscopy has been used as a method to detect tallow adulteration in butter. All of these parameters and measurements have been studied using NIR spectroscopy with results showing the potential to replace traditional reference methods.
References
Overview of The Buttermaking Process
https://www.uoguelph.ca/foodscience/book-page/overview-buttermaking-process
The Steps Involved in Butter Production Process
http://food-beverage.ezinemark.com/the-steps-involved-in-butter-production-process-7d35275213af.html
How to Make Butter
http://www.countryfarm-lifestyles.com/how-to-make-butter.html#.XGcCb_ZFxRd
What Is Cultured Butter
https://www.leaf.tv/articles/what-is-cultured-butter/
Aged Butter
http://nordicfoodlab.org/blog/2016/1/21/aged-butter-part-1-background-and-basics
http://nordicfoodlab.org/blog/2016/1/29/aged-butter-part-2-the-science-of-rancidity
At-Line Near-Infrared Spectroscopy for Prediction of the Solid Fat Content of Milk Fat from New Zealand Butter – Meagher, Holroyf, Illingworth, et al., Journal of Agricultural and Food Chemistry, 2007, 55, 2791-2796 https://pubs.acs.org/doi/abs/10.1021/jf063215m?journalCode=jafcau
Robust New NIRS Coupled With Multivariate Methods for the Detection and Quantification of Tallow Adulteration in Clarified Butter Samples – Mabood, Abbas, Jabeen, et al., Food Additives & Contaminants: Part A, 35:3, 404-411
https://tandfonline.com/doi/abs/10.1080/19440049.2017.1418090?journalCode=tfac20