Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Patent
1988-08-29
1991-04-09
Walberg, Teresa J.
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
99328, 219492, 219521, H05B 102
Patent
active
050066900
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electric toasters, that is devices for toasting slices of bread or other toastable items of food.
Conventional electric toasters operate by heating a slice of bread or other item of food by means of one or more radiant (red hot) heating elements located close to (but spaced from) the bread or other item. Usually, the item to be toasted is positioned, with the aid of one or more grids or grilles, midway between two radiant heating elements. The degree of browning (toasting) of the item to be toasted depends upon the period of time during which the item is heated by the heating element(s). The period of time is manually adjustable to enable adjustment of the degree of browning. As is well known, the control of the degree of browning produced in this way is rather crude. Thus, the degree of browning produced for a given period of time will vary in dependence on various factors, such as: granary bread). porous or lumpy. will differ as between cases in which it is stale or fresh, pre-sliced or freshly sliced, and frozen or at room temperature. the spacing between the heating elements and the surface(s) to be toasted. the start of the toasting period.
Thus user of the toaster may, by trial and error, adjust the toasting time in an attempt to produce an optimum setting at least for a particular supply of items to be toasted (for example slices of bread from a particular pre-sliced loaf) on a particular occasion. This enables a crude form of compensation for factors (i) to (iii) above.
With regard to factor (iv) above, some toasters employ sophiscated self-centering mechanisms which hold a slice of bread centrally between two heating elements. This should ensure approximately even browning of the two toasted surfaces, though it will be appreciated that, for a given period of time, the degree of browning of the two surfaces will increase as the thickness of the bread is increased (and the spacing from the elements is therefore reduced).
Factor (v) above, which results in an inability to produce a batch of toast of consistent quality, using a supply of identical slices of bread, without constant adjustment of the toasting period during toasting of the batch, is a frequent source of complaint from toaster users. To compensate at least partly for this disadvantage, conventional toasters may be fitted with an ambient temperature compensation device which reduces the toasting period as the average temperature within the toaster increases with repeated use.
In summary, conventional toasters aim to enable the user to produce toast of a certain colour by attempting to provide a crude correlation between the toasting time, sometimes with ambient temperature compensation, and the degree of browning produced. It is left to the user to ascertain, by trial and error, which setting or settings of the toasting period is needed for a particular type of bread (or other item) to be toasted.
As well as the disadvantage mentioned above, conventional radiant toasters are subject to mechanical factors which can affect the quality of the toast. For example, a non-uniform heating element can produce non-uniform toasting, and poor design of the grids or grilles can produce "striping" of the toast, that is linear regions of a reduced degree of browning. Further, high internal temperatures associated with the use of radiant heating elements can lead to design problems.
European Patent Application Publication No. EP-A-0 187 492 discloses a toaster comprising a pair of electrically heatable plates which have toasting surfaces that are brought into contact with opposed surfaces of a slice of bread or other item to be toasted. Naturally, since the plates are brought into contact with the bread or other item, they are heated to a temperature (as little as 250.degree. C.) which is rather less than the temperature of the radiant (red hot) heating elements used in conventional toasters. According to EP-A-0 187 492, control of the degree of browning is achieved, as in conventional toasters, by adjusting the period or duratio
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Cole Graham M.
Shave Percival J.
Dreamland Electrical Applicances plc
Walberg Teresa J.
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