The oil runs to the edge of the pan? The pan wobbles?

Perhaps you have already noticed this with a new pan: The oil runs from the middle to the edge of the pan, especially with non-stick pans. Or the cold pan wobbles a little on the glass ceramic hob surface (ceramic or induction cookers). Or the base seems to be not completely flat.

Quite a few customers think that these are signs of a manufacturing or material defect. Therefore, customer questions regarding these phenomenons are among the most frequently asked questions.

The reason for what was described at the beginning is the concave shape of the cookware bottom.

Concave bottom (hollow curvature)

Many customers think that a cookware base must be absolutely 100% flat. This is not true, because physics stands in the way: metal expands when heated, as is known. Everyone has seen old tracks running in serpentine lines under the glistening sun of Australia or Africa. The metal of the track expands and if there is no possibility of further expansion in the longitudinal direction, said serpentines are formed.

Well, a pan that gets a totally wavy bottom when heated strongly would be extremely impractical. The bottom would warp convexly, like a bowl and permanent deformations would render the cookware unusable.

The base of pots, pans and roasters is thus given a shape that anticipates the expansion in the opposite direction when heated, so that the cookware is still firmly and securely on the stove even during heavy frying. This is achieved by a concave bottom shape. This form is designed for a maximum operating temperature, so that a certain concave, hollow curvature can remain during normal frying.

This, of course, has the disadvantage, especially with low-fat frying, that the oil can drain noticeably to the edge. Depending on how pronounced the concave shape of the bottom is this can never be completely prevented and must be tolerated.

Both for the magnetic waves of an induction cooktop and for the heat radiation of a radiant heat stove (ceramic / halogen type cooktop), the deviations from perfect flatness that are technically necessary for cookware and the resulting minimal empty spaces between the cooktop and the cookware do not generally pose a problem in terms of hindering functionality.  

Bimetal-effect: special case induction-compatible aluminum cookware

It should be noted that the thermal expansion of the base and, as a result, the change in the hollow curvature varies according to the type and size of cooker and, last but not least, the base construction of the cookware. For example, in the case of induction-suitable aluminium and cast aluminium cookware, there may be a tendency to an increase in the hollow curvature during heating. Why is that? Well, aluminum is an excellent heat conductor, making it ideal for cookware, but unfortunately it is not ferromagnetic and thus not suitabe for induction cookers. To overcome that and to make aluminum cookware usable on induction cooktops, a plate of ferromagnetic stainless steel is applied to the base of the aluminum cookware. This is done by impacting or modling of a punched stainless steel disc on or in the aluminum body, or, the technologically more sophisticated and more expensive variety, by welding on a full disc stainless steel disc (Full Disc Induction), very rarely also by plasma spraying technology.

However, the two metals of the base (body made of aluminum and base plate made of stainless steel) do expand to different degrees during heating because they have different coefficients of thermal expansion. Consequently, the aluminum expands more than the stainless steel does. But since both metals are connected for good heat transfer, the aluminum basically expands "over" the stainless steel plate that limits its expansion. That causes an increase of the concave curvature and it can let the oil run to the edge more when the pan is hot than when the pan is cold. This effect is purely physical and is under no circumstance a claimable material defect!

But since this effect only occurs with aluminum cookware that is always coated anyway (either a non-stick coating or ceramic coating), and the oil used is therefore usually filled sparingly and not covering the bottom anyway, the bimetal effect does not usually play a significant role for the frying success. Simply turn the food in the oil in the pan so that it is covered all around, and you will have no problems frying. If you are frying something in the pan that requires a closed oil film (deep-frying schnitzels etc.), you will have to add a little more oil as an exception. 

If in doubt, choose a model with a particularly thick base (6-8 mm), as this effect will be less noticeable here. Of course such a thick cookware is also noticeably heavier and takes longer to heat up, but even with cookware the following applies: All good things never go together....

If you just cannot accept the inherent bimetal-effect of all-hob-capable / induction-suitable aluminum cookware, choose a stainless steel or cast iron cookware instead.

And if you do not have an induction cooktop and also do not plan to get one, you can simply choose an aluminum cookware that is not induction-suitable, so one that does not have a stainless steel plate on the base, e.g. the Granitica Extra series or Gran Sasso Plus by Barazzoni or the Granito Hard Stone series by Risolì.

"But my other frying pan is perfectly flat."

Often we have already heard such and similar sentences when explaining the topic of the concave cookware base. Be assured, however, that no modern cookware is 100% flat. The reason why some cookware seems completely flat to the layman at first glance is simply due to the fact that there are two typical courses of the hollow curvature of concavely shaped bottoms: concentric and longitudinal courses.

In case of a concentric course, the base of the cookware lies flat all around and without wobbling; the holow space (YELLOW) in the center between the hob surface and the base of the cookware is not visible.

In case of a longitudinal course, there are usually two edges along a longitudinal axis of the bottom sitting on the hob. A slight wobbling of the cold cookware is particularly noticeable on flat and expansion-neutral glass ceramic surfaces. The slight wobbling usually subsides during heating.

Both types of concave shape are common in industry. Price and brand of the cookware per se are no indication for one way or the other. However, the hollow curvature of a thick base can often be concealed better by clever shaping and is therefore less noticeable. 

Oval or rectangular frying pans, pots and casseroles

Things get particularly difficult with cookware that is not round, e.g. oval or rectangular. Since the size of the cooking zone rarely corresponds exactly to the size of the base of such cookware, the thermal expansion in the base of the cookware is correspondingly uneven; this can lead to considerable tension in the structure of the base. The course of the concave shape usually runs longitudinally here and is slightly larger so that the bottom does warp like a bowl when frying on high heat.

Yet still, especially with large oval or rectangular cookware, whether made of cast iron or of aluminum, whether it is suitable for induction or not, whether it may be inexpensive or price-intensive, there will always be a certain amount of unevenness, not only when cold but also at operating temperature, which is of course escpecially noticeable on an expansion-neutral glass ceramic surface.

Please adapt your approach to cooking to account for that and please take special care to heat rectangular / ovale cookware slowly and gradually so that the heat can be better distributed throughout the cookware.

Not a reason for a complaint

Please note that the presence of a proper concave bottom shape proper does not constitute a defect and therefore we do not accept this as a reason for a complaint.

Recommendation

For customers placing extra value on cookware where the bottom's concave shape is as small as possible and hardly noticeable we recommend round cast aluminium or (especially for induction) stainless steel cookware with a very thick base (> 5 mm).

If you have any further questions in this regard, please contact us if possible before purchasing in order to obtain advice on product selection, as the type and design of the concave bottom shape are in no way dependent on the brand or price of the cookware, but only on model-dependent material and technical production factors.

First check, then use!

If the cookware item has already been delivered, please check, if necessary, BEFORE using the cookware, whether the bottom curvature of the item is okay for you. Carefully remove the product packaging so that if you do not like the item, you can return it without any possible deductions as part of the revocation.

There are distinct advantages of coated cookware which we would like to explain to you below. We also want to explain the clear differences in the properties. You should choose the right coating for the intended purpose, e.g. a high non-stick effect for fat-free cooking of pancakes and other egg-based dishes.
 

Non-stick coating

BERNDES usually uses strong triple-layer coatings comprising the following layers: primer, middle layer and top layer. Non-stick coating is based on a plastic, more precisely polytetrafluorethylene (PTFE). Since its discovery about 40 years ago, there have been no signs of health risks from its processing or use. This PTFE can be used up to a maximum sustained temperature of 260 °C/500 °F. That's much too hot for cooking foods, and most fats and oils burn off well below this temperature.
We won't go into PFOA or PFOS because we don't use either of these hazardous substances in our coatings.
After the coating is applied to the cookware, it is fused on in a sintering furnace at approx. 430 °C/806°F. This process must be very precise because the temperature control in the furnace is a decisive factor for the quality of the finished article. First, slow heating ensures the water in the coating evaporates before the start of the high-temperature drying and hardening process. The properties of the middle and top layers (hardness and non-stick effect) combine during the drying process. In this way, BERNDES guarantees:
·High non-stick properties
·Long life with correct care
·High and lasting colour-fastness
·Hardwearing quality in practical use
 

Ceramic coating

This kind of coating has only been in use for a few years and is currently very popular because it can be used for white or coloured surfaces. Like PFTE non-stick coatings, this type of coating is also safe to health. In contrast to non-stick coating, ceramic coating is extremely hard and scratch-resistant. However, similar to enamel, the hard coating is vulnerable to impacts, especially on the edges of pots and pans! If you use an induction or gas cooker, you will benefit from the high heat-resistance. Ceramic coatings usually consist of several components blended together. They are burned on at a temperature of 220 °C/428 °F, which triggers a chemical process that produces the final hardness. You should know the following about ceramic-coated cookware from BERNDES:
·The production process produces extremely hard and scratch-resistant coating and non-stick properties, however these decline over time and are not comparable with the non-stick properties of a PTFE coating.
·CAUTION: Although other manufacturers suggest in their marketing that you can fry fat-free in ceramic-coated cookware, this is not true. Many customers believe these claims and have been disappointed.
The sustained heat resistance is much higher at 400 °C/752 F, and overheating does not cause any risk to health. However, this property is actually irrelevant because nobody should work with temperatures above 200 °C/392 °F when most oils and fats have already burned away.
·The sustained heat resistance is much higher at 400 °C/752 F, and overheating does not cause any risk to health. However, this property is actually irrelevant because nobody should work with temperatures above 200 °C/392 °F when most oils and fats have already burned away.
·The BERNDES ceramic coating is ideal for searing or browning e.g. fried potatoes, steaks, turkey strips and other meat
·Easy to clean
·No PFOA is used in the manufacturing process
·Almost all colours are possible
 

"Non-coated"/stainless steel

BERNDES also supplies non-coated cookware with stainless steel as the basic material, which is also safe to health. There are no limits to its heat resistance, similar to ceramic coatings. However, high temperatures are not really useful because oils and fat burn away from temperatures of 210-220 °C/410-428 °F. Stainless steel itself is a poor heat conductor. That's why stainless steel cookware often features a capsule base with a copper or aluminium plate inside (see Cookware bases). Stainless steel does not come with non-stick properties, so food can burn on at high temperatures and is difficult to clean off afterwards. For this reason, when you use stainless steel cookware, always add oil or fat for frying or water for boiling. This prevents the food from sticking. It is important to add salt to the water only when it is boiling, otherwise salt deposited on the bottom of the pan can cause pitting of the stainless steel surface. Any blue stains may be caused by minerals in the food and are completely safe. You can remove them with a little citric acid.

Different bases for different cooker types

Cookware needs to function on as many types of cooker as possible. Induction cookers, which are becoming more and more popular, are a special case. All our products are suitable for electric, gas and glass-ceramic hobs. For induction cookers, the base must have a ferro-magnetic layer. We always indicate on our products what types of cooker they are suitable for.
 

BERNDES CD-Boden®

What's special about this base is that after it has been ground flat it receives a light texturing that allows it to expand towards the hob plate when hot so it sits on the hob plate perfectly flat. No energy is wasted heating air and the cookware rests firmly on the cooker. Another advantage is that the base heats up evenly, something which is incidentally true of all BERNDES cookware! These bases are regularly tested in our lab according to DIN 44 094 and DIN EN 12 983-1. This involves heating the empty product to 200 °C/392 °F then immersing it in cold water up to 50 times. The base must retain its shape without any deformation!
 

Induction capsule base

This kind of base is used very commonly for stainless steel cookware. Today, pan bodies are usually made of chrome-nickel-steel and the bases consist of ferritic stainless steel that reacts to magnetic force and is therefore suitable for induction cookers. Stainless steel itself is a poor heat conductor. That is why a material with good heat conducting qualities such as aluminium or copper is integrated in the base.
 

Pressed induction bases

A magnetisable plate is pressed onto the aluminium body on a press applying a force of up to 3,000 tons. The energy applied here fuses the two materials together. To ensure a long service life, we advise you not to use a dishwasher because aggressive cleaning agents wash out the aluminium and the plate eventually comes loose. Please also note our care instructions
 

Premium induction:

In 2009 we upgraded the cast aluminium products in our PROFESSIONAL series with a special premium induction base featuring a unique non-distorting, smooth and very hard surface. In a cold gas injection process, we spray ferritic stainless steel powder at high kinetic force onto the aluminium base. This micro-welds the fine particles to the base. That's why the bases in the PROFESSIONAL series are extremely durable and do not scratch the cooker surface. Furthermore, these products are suitable for all types of cooker!

Over the ages, humankind has used many different materials for cookware. Each material has different requirements and properties. Apart from clay vessels, copper kettles or uncoated aluminium cookware, above all cast steel pots and pans have been used in more recent human history. Ever higher requirements relating to cooking and cleaning triggered the development of stainless steel, aluminium and cast aluminium cookware as well as non-stick coatings. Today, BERNDES focuses on cookware made of stainless steel, aluminium and cast aluminium.
 

Stainless steel

The starting point for stainless steel products is a stainless steel blank (flat disc). This is greased, placed in a hydraulic drawing press and shaped over a so-called deep-drawing die. Next, the edge of the raw body is punched so that the finished cookware has a clean pouring edge. For better heat conduction, stainless steel bodies are fitted with a capsule base. Aluminium is integrated in the capsule base to optimise the absorption and transfer of heat.
 

Aluminium

A circular aluminium disc (blank) is used for the pan or frying pan. BERNDES uses discs between 3 and 5 mm thick. We use two different production methods and exclusively process aluminium alloys approved for contact with food.
 

Deep-drawing

Similar to stainless steel processing, the aluminium blank is greased and placed into a hydraulic drawing press where it is shaped over a deep-drawing die. Depending on the product size and blank thickness, a weight of up to 200 tons is applied for this forming process. The advantage of deep-drawn parts is an even thickness of base and walls. This ensures good heat conductivity.
Impressing die forging (also called closed-die forging)
Again, this involves forming an aluminium disc. The press works with two dies (top and bottom tools) which it slams together, applying pressing forces of up to 4,000 tons. The finished cookware produced in this way has an almost identical appearance to cast parts (see Cast aluminium), however, the two types differ in heat conductivity and heat retention.
 

Cast aluminium

Aluminium has only been used for about 200 years. That may seem a long time, but compared to the above materials it is a very young addition! What makes cast aluminium ideal for cookware is its optimal heat conductivity und heat retention as well as its light weight. The casting process involves injecting liquid aluminium into a pre-shaped casting mould under vacuum. This ensures there are no air bubbles. The advantage of this process is that even complex shapes are possible which can not be made from aluminium blanks, e.g. frying pans with grilling ridges, rectangular shapes or deep casseroles with cast-on handles. The result is perfect material distribution for every product.

Cookware is much more complex than it appears at first glance. There are many factors that influence the quality and service life of pots and pans! What makes the difference are not only the materials we use, but also our expertise and experience. All this, combined with our high quality standards, defines each one of our products. Over its long corporate history, BERNDES has not only acquired know-how, but also developed many innovations. That is why BERNDES is today a leading specialist in non-stick-coated cast aluminium cookware.
Before you buy a new item of cookware, it is a good idea to find out a few facts so that you can choose the best products for your needs! Here is some more detailed information to help you make your decision.

To keep your high-quality cookware in good condition, we recommend using wooden or plastic utensils. All cast aluminium cookware with non-stick coating on the market contains plastic (PTFE). Due to its nature, plastic is more vulnerable than stainless steel or other metals. Scratching, scouring and cutting damage all non-stick coatings! Some manufacturers claim that their coatings are completely resistant. But they are coated with only a very thin non-stick layer. That means the non-stick effect wears off very quickly.

No! Neither the pan's functions nor your health will be adversely affected by a few knife scratches or stains. No coating is absolutely non-porous. That's why microscopically tiny fat residues get trapped and can cause stains. We recommend careful cleaning and the use of plastic or wooden utensils. Our tip: You can lighten stains caused by fat by cleaning with lemon juice. Deposits that are burned on again and again can no longer be removed and negatively affect the non-stick properties.

An optimal life of the cookware is achieved if you dispense with a cleaning in the dishwasher. The cleaning agents are often too aggressive and attack the material in the long term.
For cleaning, hot water, detergent and a soft sponge are sufficient. For sealed cookware, wiping with a kitchen towel is not enough. Fat remnants must be completely removed as otherwise they may burn into the seal on renewed heating and cause overheating damage.

All products with S.S handles are completely oven-proof because the handles are made of the same heat-resistant S.S material. In contrast, all products with plastic handles are only oven-proof up to a temperature of 160 °C/320 °F. We advise against using cookware with wooden handles in the oven because this causes the wood to dry out and become porous.