What is a burr grinder
A burr grinder consists of 2 blades with their contact adjustable for the fineness of the resulting ground coffee. There are 2 types, steel burrs and ceramic burrs with 2 different designs, flat burrs and conical burrs. The difference between a burr grinder and a blade grinder is that a burr grinder doesn’t add heat to the coffee during grinding, ensuring the coffee flavour not affected.
Steel vs Ceramic burrs and heat generation
Points to consider in brief:-
- Ceramic burrs are harder than steel, lasting (on average) about twice as long as steel burrs.
- Ceramic burrs are more brittle than steel. A very hard foreign matter, such as rock in beans, could damage it.
- Ceramic burr are less thermally conductive than steel, transferring less heat than steel burrs
- Ceramic burrs are ideal for heavy duty such as commercial applications.
- The material of the burr has no bearing on the speed it must rotate, this is a function of the design of the teeth.
- The noise generated during grinding is due to the design of the grinding ridges not the material of the burr.
- Ceramic and steel burrs both handle all roasts equally.
- Steel burrs may be more durable than ceramic if a stone is encountered, but the steel burr can dent or be damaged aw well.
Heat and grinding coffee beans:
Thermal conductivity of the burrs has no influence on the cause of heat built up in grinders which comes from a combination of internal friction as the coffee bean is crushed, and from minor friction in the actual grinding of the bean by the burrs.
The sharper the burrs, the less heat is generated in grinding coffee beans. The majority of heat generated in due to crushing the beans and then transferred to the burrs. For steel burrs, they will transfer this heat away from the coffee to the housing of the grinder. The actual surface temperature of the grinding surface will be similar whether the burr is steel or ceramic, except for that heat which is able to transfer through the burr and away from the coffee.
In large coffee grinders for industry application, the burrs are mounted to a metal plate with water cooling. The burrs conduct the heat away from the beans (and the grinding surface) to the water via the metal plate. Another source of heat in ground coffee comes from heat stored in the burrs and grinder housing from preceding grinding(from coffee ground earlier or immediately preceding) and transferred back into the coffee being ground.
The rotation speed of the grinding burrs and the effect of heat accumulated in the ground coffee
Poorly designed burrs, both steel and ceramic burrs, will result in inefficient grinding of the coffee and generating more heat in the coffee beans. The actual speed of rotation of the burrs is not the leading variable. A well-designed conical burrs can rotate at 3400 rpm, grinding 10+ grams per second, with the coffee coming out cool. Most conical burr grinders rotates at 300-500 rpm.
The surface of the burrs obtain heat from preceding grinding and the hot surface of the burrs can then conduct this heat back into the new coffee. A well-designed coffer grinder with sharp burrs and a good design of grinding chamber, the coffee passes through the grinding ridges rapidly. The contact duration is negligible. The only heat encountered by the coffee is from crushing and cutting of the coffee beans not from the latent heat in the burrs nor the grinding housing.
Flat Burr vs Conical Burr
What is a Conical Grinder
A conical grinder contains two cone-shaped “burrs”, the grinding mechanisms. The ridges on the burrs grind or crush coffee beans to the desired fineness. One burr remains in place while the other turns to expedite the crushing or grinding functions.
A conical grinder rotates slower than a flat burr grinder, producing less noise, in parallel, creating less friction. The latter is important because less heat building up inside the grinder chamber. In long operation, this will help to preserve the flavor of coffee, because fewer oils will vaporize during grinding.
Other advantages include:
- Fewer clumps accumulated
- Producing less mess because static charge is greatly reduced
- Offering greater control over the level of fineness
What is a Flat Burr Grinder
A flat burr grinder contains two flat “burrs”, the grinding plates facing each other. As with conical grinders, one burr remains stationary while the other rotates. Instead of having ridges to crush and to grind the beans, the grinding functions are performed by the “teeth” on the edges of the flat plates.
Flat Burr Grinder Advantages
When comparing a flat burr vs. conical grinder, the biggest advantage is price. These grinders tend to cost less than conical burr grinders, making them ideal for anyone who is on a budget. Other advantages include:
- Costs less than conical burr grinder
- Provides more consistent results than a manual or blade grinder
- Easy to adjust for various levels of coarseness or fineness
- Requires little maintenance
Flat Burr Grinder Disadvantages
- Burrs may easily become clogged on grinding large quantities of beans
- More heat is generated compared to conical burr grinders
- Possibly create more mess on account of the increased static charge
Flat burrs are assumed largely enhancing the fruity tones of coffee beans while conical burrs may improve the sweetness and draw out chocolate flavors.
Coffee Burr Grinder Overview
Quick Tip: Burrs for Coffee Grinders
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