How we test kitchen knives
By Matt Stevens
Article 4 of 7
How we test kitchen knives
The best kitchen knives don’t just cut food brilliantly, they also stay sharp for longer. Read on to find out how we test kitchen knives.
At Which? we go to great lengths to rigorously test kitchen knives to help you avoid buying one of the really poor ones that fail to cut the mustard – or much else – in our tests. You can trust that any kitchen knife we recommend really is the best for you and your home.
Our reviews answer the most crucial questions about kitchen knives – a Best Buy kitchen knife will be sharp when you buy it and will stay sharp, but a Don’t Buy won’t be very sharp when you get it home and will quickly lose any sharpness it had. Spending a lot of money in the shops doesn't necessarily get you a good kitchen knife, and we’ve found Best Buys available for under £30.
Our independent tests look at more than just how sharp the knife is when you buy it, they answer all the most important kitchen knife questions including:
- How well will it chop and slice meat and vegetables?
- How easy is the knife to use?
- How well does the knife retain its sharpness?
- How corrosion-resistant is it?
- Can I wash my kitchen knife in the dishwasher?
- How safe is my kitchen knife?
- Should I buy it?
Only the knives that do brilliantly across all of our tests can join the ranks of our Best Buy kitchen knives.
How well will it chop and slice meat and vegetables?
The most important thing about a kitchen knife is that it makes preparing food a pleasure not a chore. So each knife goes through a series of cutting tests to check how well it slices, dices and chops.
Three experienced knife users slice their way through a pile of potatoes, cucumber, tomatoes and ham; they cube carrot, swede and steak, and chop spring onions and parsley, then rate how effectively the knife cuts each item.
How easy is the knife to use?
We’re looking for knives that are easy to use. So our experts also rate the suitability of the knife for each chopping task. They check how comfortable the handle is and how secure their grip is with wet or dry hands.
The weight and balance of each knife also comes under scrutiny. Check out our Best Buys for easy-to-use kitchen knives.
How well does it retain its sharpness?
Each kitchen knife blade we test is straight out of the box. We use an automatic computer-controlled testing rig to check the initial sharpness of each knife. The knife is clamped into the testing rig with the blade upwards and makes three 4cm forward and backwards cutting strokes across a pack of highly abrasive synthetic card made from a blend of cellulose and quartz powder.
The machine automatically measures the depth of the first three cutting strokes to calculate the blade’s initial cutting performance (ICP). The deeper the cut, the sharper the knife.
The knives then make 60 forward and backward strokes, and the machine automatically measures every stroke to see how quickly the sharpness of the blade deteriorates. The blades cut less each time, as the blades get blunter.
How corrosion-resistant is it?
We check each knife for manufacturing faults that will adversely affect how well the steel stands up to corrosion.
The knife is placed in an automatic machine that dips it, two or three times each minute, into hot salty water (1% sodium chloride at 60°C). This goes on for six hours. We then inspect the blade for cracks, and measure how much of the blade has rusted.
Can I wash my kitchen knife in the dishwasher?
Some manufacturers claim that their knives are dishwasher-safe, while others don’t specify, so we run all knives through 100 washing and drying cycles at 60°C.
The knives are secured carefully in the washer racks so that they don’t touch each other and cause contact erosion. At the end of the test we scrutinise them for corrosion and damage. Our full kitchen knife test results page shows which of the knives that we have tested are safe to wash in the dishwasher.
How safe is my kitchen knife?
Aside from numerous drop tests, we also subject the knives to bending and twisting tests to check for any permanent deformation or cracking of the handle or blade.
Should I buy it?
70%the score a kitchen knife needs to earn our Best Buy recommendation
All of the assessments listed above go into making the final overall score for each kitchen knife that we review. Because we know what's most important to you, some elements are more important than others, so carry different weights:
- 60% Sharpness and cutting performance
- 25% Ease of use
- 15% Safety and durability
A kitchen knife needs to score more than 70% to be considered a Best Buy kitchen knife. Those scoring below 40% are highlighted as Don't Buy kitchen knives – they are so bad that we think you should avoid them altogether.