To grind peanuts into peanut butter, various types of equipment are used, such as disk mills, homogenizer mills, tooth mills, and colloid mills. Most of these mills allow for adjustment of the grinding gap, enabling process conditions to be tuned based on hourly production output and grinding requirements.
Peanut butter production typically involves using two mills in combination. The first mill breaks down the peanuts to a medium particle size, and the second mill further grinds them until a smooth, delicate texture is achieved. For fine grinding, the gap between the grinding plates is typically adjusted to between 0.81 mm and 0.076 mm.
Sometimes, the largest ground peanut particles are about one-eighth the size of a whole peanut kernel. These are mixed with peanut butter of other particle sizes to create chunky-style peanut butter. Alternatively, specially designed grinding plates can be used instead of standard plates for processing peanuts.
Additives, comprising approximately 2% of the total weight and including ingredients such as salt, sweeteners, and others, can be uniformly fed into the grinder along with the peanuts. The heat generated during grinding can melt hydrogenated oil, or the fat can be pre-warmed and melted before being added to the grinder. To prevent overheating, the mills are water-cooled. These grinders are adjustable and offer advantages such as automatic feeding (for both salt and peanuts) and easy cleaning.
Throughout the processing, a consistent pressure must be maintained to prevent air from being incorporated into the peanut butter, which can cause bubbles to form. Using gravity and a screw feeder to introduce peanuts into the grinder, along with continuously removing air from the peanut butter, helps prevent oil oxidation and extends the product’s shelf life.
Liquid additives can be introduced into the grinder using a peristaltic pump. Stabilizers for peanut butter can include hydrogenated vegetable oil, mono-glycerides, di-glycerides, or a mixture of mono- and di-glycerides. Dry additives like salt and sugar can be proportionally fed into the grinding machine using a vibratory feeder or screw feeder. Alternatively, other additives can be uniformly blended into the peanut butter after mixing.
The ground peanut butter is then conveyed to the packaging machinery. Between these stages, it’s necessary to incorporate a scraped surface heat exchanger, equipped with spiral scraper blades that propel and grind the product, facilitating cooling.
The stabilizer dosage generally does not exceed 5.5%, with 3.5% being the typical amount. The exact amount can vary based on the peanut’s oil content and the mixing method. Stabilizers are often added separately through a dedicated device at the top of the system. The optimal temperature for mixing stabilizers is between 60°C and 90°C.
When mixing additives in a container, avoid overfilling; a load of around 115 kg is suitable for achieving a homogeneous mix. For filling, the recommended temperature, depending on the stabilizer and filling equipment, is between 30°C and 44°C.
The grinding and mixing processes generate heat. Using a spiral heat exchanger before packaging can directly promote fat crystallization. Typically, peanut butter needs to be cooled from about 77°C down to 50°C or lower. Within 48 hours after packaging, and if stored at a temperature of around 15°C or below, crystallization continues within the container. Poor cooling control can lead to inadequate crystallization, potentially causing thermal degradation or shrinkage at the center of the container.
For chunky peanut butter, peanut granules are added and mixed into the smooth peanut butter just before filling. Producing varieties like chocolate, peanut butter, or strawberry jelly peanut butter requires specialized filling equipment.
A concave surface forming on the peanut butter after packaging might be due to entrapped air (if the product wasn’t deaerated) contracting at lower temperatures. Fat also contracts upon cooling, forming unstable crystals which then transition into more stable forms with higher melting points. A convex surface can result from overfilling and subsequent temperature increase. Therefore, containers should be filled slightly less than full capacity.
The presence of solid fats influences crystallization. Preventing oil separation in peanut butter is improved by the crystallization of hydrogenated oils. The best method to avoid oil separation is cooling under agitation, which facilitates the formation of finer crystals.
If the fat stability in peanut butter is good, it can prevent spoilage caused by oil rising and oxidizing. Properly stabilized peanut butter can have a shelf life of up to two years when stored at a temperature below 26°C, even under visible light. Oil oxidation at the top can destabilize the product, a process that can continue even after the jar is sealed.
Additive blends for peanut butter stabilization can also consist of edible plastic fats, flavorings, sucrose, fructose, glucose, or corn syrup combined. Some peanut butters use hydrogenated peanut oil (with a melting point of around 64.4°C and an iodine value of 8) blended into the butter for stabilization. Other methods involve combining hydrogenated peanut oil, salt, and an equal amount of other fats before adding them to the peanut butter. Hydrogenated rapeseed oil is also used for stabilization.
The U.S. Food and Drug Administration (FDA) recommends that peanut butter contain at least 90% peanuts, with the remaining 10% consisting of other ingredients. The total fat content in the final product should not exceed 55%.
Depending on its intended use, peanut butter can have different roast color requirements, categorized as light roast, medium-light roast, medium roast, or dark roast. Color assessment can be done by comparing against standard color charts or by using colorimetric instruments. Precise color comparison can be achieved using the Lovibond Tintometer for fats and oils.
