For peanut butter production, peanuts must be free from mechanical impurities such as soil, sand, stems, and leaves. The presence of aflatoxin is strictly prohibited.
In the production of both stabilized and flavored peanut butter, various additives are required, which can amount to up to 12% of the total formulation. These include stabilizers, antioxidants, sweeteners, flavor enhancers, and proprietary secret ingredients.
1. Peanut Shelling
Common peanut shelling (dehulling) methods include the following two types:
- Manual Shelling: This involves manually separating shells and kernels. It is suitable for small-scale production or when producing high-grade peanut kernels for premium food products.
- Mechanical Shelling: Common machinery includes disc shellers, centrifugal shellers, blade shellers, and high-speed air-stream shellers.
After shelling, the kernels and shells need to be separated. The primary methods used are screening (sieving) and air separation (winnowing). Consequently, shelling equipment often integrates screening and air separation systems, enabling shelling and kernel-shell separation in a single process.
2. Peanut Grading
(1) Purpose of Grading
The purpose of peanut grading is to achieve uniform size and specifications, which is essential for producing high-quality peanut products.
(2) Grading Standards
A widely used grading standard is the “count” system, which refers to the number of peanut kernels per ounce.
Peanut kernels are generally divided into four grades:
- Small Kernels: 60-80 count per ounce.
- Medium Kernels: 40-60 count per ounce.
- Large Kernels: 30-40 count per ounce.
- Extra-Large Kernels: 20-30 count per ounce.
A variance of 10 kernels is allowed for the small grade, five kernels for the medium and large grades, and only two kernels for the extra-large grade.
(3) Grading Methods
- Manual Grading: Kernels (or pods) of consistent size and uniformity are sorted by hand in accordance with the grading standards. The advantage is high-quality grading; the disadvantages are low efficiency and high cost.
- Mechanical Grading: The main working component of mechanical graders is the grading screen/sieve. These screens are manufactured to specifications based on the standards for different peanut kernel (or pod) grades and are fixed to a frame to form the screening surface. The advantages are labor savings, high grading efficiency, and low cost. The disadvantage is that the quality may not be as high as manual grading.
(4) Peanut Kernel Grading Equipment
Peanut kernel grading equipment typically consists of a frame, particle selection/grading screens, a fan/blower, a transmission device, and control mechanisms.
Simple sorting machines typically have two or three layers of screens with varying aperture sizes, enabling kernels to be sorted into three distinct grades. For export purposes, machines with screens featuring multiple aperture specifications are used to sort kernels into more grades.
Commonly used peanut kernel cleaning and grading machines are mainly composed of a feed hopper, a vibrating feed table, a specific gravity destoner screen, upper and lower fans, a cylindrical grading screen, three hoppers (for large, medium, and small kernels), and a frame.
These machines operate primarily by exploiting differences in the physical and mechanical properties (such as density and suspension velocity) and geometric dimensions between peanut kernels and impurities. They perform cleaning by leveraging the different aerodynamic characteristics and densities of kernels and impurities, using air streams in combination with vibrating screens. Grading by kernel thickness is achieved using an inclined cylindrical screen.
