Method for operating dishwasher having measuring unit for measuring pH value of washing liquid

Abstract

The invention relates to a method of operating a dishwasher. The dishwasher comprises a tub (1) for loading dishes, a detergent reservoir (11) for dispensing detergent and a circulation system for circulating washing liquid. After the start of the washing process, a first amount of dishwashing detergent is added to the washing liquid. Primary measurements are taken for determining the pH value of the washing liquid. An additional amount of dishwashing agent may be added to the washing liquid, wherein the amount depends on the pH value of the washing liquid as determined by the primary measurement.

Description

Technical Field

[0001] The present invention relates to a dishwasher and to a method for operating the dishwasher. The dishwasher comprises a tub for loading dishes, a detergent reservoir for dispensing dishwashing detergent, and a circulation system for circulating the washing liquid. The invention also relates to a dishwashing detergent for use in the method and for use in the dishwasher. Background Art

[0002] Nowadays, dishwashing detergent is often provided in the form of tablets. The user inserts the tablet into a container that is often located on the inside of the dishwasher door. Alternatively, the user can fill the container with detergent in powder form or with liquid or gel detergent.

[0003] The tablets have a predetermined size. For each wash cycle, the same amount of detergent is inserted into the dishwasher, regardless of the number of dishes arranged in the tub and the soiling of the dishes. If liquid or powdered detergent is used, the user typically fills the container to the maximum mark to ensure that there is enough detergent available for the wash cycle.

[0004] In most cases, a smaller amount of dishwashing detergent will be sufficient or may achieve the same results if the amount of some components of the detergent is reduced.

[0005] definition

[0006] Unless otherwise stated, the following definitions shall apply to this specification:

[0007] As used herein, the terms "a," "an," "the" and similar terms used in the context of the invention (especially in the context of the claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[0008] As used herein, the terms "comprising," "containing," and "including" are used herein in their open, non-restrictive sense. It is understood that the various embodiments, preferences, and ranges may be combined arbitrarily. Thus, for example, a solution comprising compound A may comprise other compounds in addition to A. However, the term "comprising," as a specific embodiment thereof, also covers the more restrictive meanings of "consisting essentially of" and "consisting of," such that, for example, a "solution comprising A, B, and optionally C" may also consist (essentially) of A and B, or (essentially) of A, B, and C. As used herein, the transition phrase "consisting essentially of" (and grammatical variations) should be interpreted as including the recited materials or steps and those that do not materially affect the basis and novel characteristics of the claimed invention. Therefore, the term "consisting essentially of" should not be interpreted as being equivalent to "comprising."

[0009] As used herein, the term "about" means that the amount or value in question may be the specific value specified or some other value around it. Generally, the term "about" indicating a value is intended to indicate a range within ±5% of that value. As an example, the phrase "about 100" indicates a range of 100 ± 5, i.e., a range of 95-105. Preferably, a range indicated by the term "about" indicates a range within ±3%, more preferably ±1%, of that value. Generally, when the term "about" is used, it can be expected that similar results or effects according to the present invention can be obtained within a range of ±5% of the indicated value. Summary of the Invention

[0010] The problem addressed by the present invention is to provide a method for operating a dishwasher with optimized dishwashing detergent consumption.

[0011] This problem is solved by a method for operating a dishwasher according to claim 1. The dishwasher comprises

[0012] A tub for loading the dishes; in particular at least two baskets are arranged in the tub and can contain the dishes to be washed.

[0013] - A detergent reservoir for dispensing dishwashing detergent. In particular, the detergent reservoir may be a tank suitable for dispensing liquid detergent, solid detergent or gel detergent, in particular wherein the solid detergent is in powder form or granular form.

[0014] A circulation system for circulating the washing liquid. In particular, the washing liquid is collected at the bottom of the dishwasher, pumped to spray arms arranged in the tub and sprayed onto the dishes in the tub.

[0015] The method comprises the following steps, in particular in the following order:

[0016] a) starting a first washing process, in particular wherein the washing process is initiated by a user;

[0017] b) adding a first amount of dishwashing detergent to the washing liquid; in particular, the dispensed first amount can be the same amount for each washing process. In particular, it can be different amounts if different washing programs are performed (speed program, standard program, intensive program, etc.), but the same amount of detergent can be dispensed for each washing process of the same washing program. The amount can be adjusted over time according to the user's behavior. The first amount is selected so that in most cases it is a sufficient amount for the entire washing process. In rare cases, if the pH value of the washing liquid drops below a certain pH target value during the washing process, the first amount of dishwashing detergent may be insufficient for the entire washing process.

[0018] c) Performing a main measurement for determining the pH value of the washing liquid. In particular, the main measurement is performed after a certain operating time has elapsed but before the washing process has been terminated.

[0019] d) If the pH of the wash liquid determined by the primary measurement is below the pH target, an additional amount of dishwashing detergent or an alkalinity source is added to the wash liquid. The dishwasher will not always perform this step because in most cases the measured pH will be greater than the pH target and there is no need to add an additional amount of dishwashing detergent. However, in the event that the measured pH is below the pH target, additional dishwashing detergent or an alkalinity source is dispensed into the wash liquid because an alkaline wash liquid is required to achieve good washing results. The alkalinity source can be selected from alkali metal carbonates as described herein, alkali metal hydroxides as described herein, alkali metal silicates as described herein, and mixtures thereof, and can contain from about 0.001% to about 0.5% by weight of a pH sensitive dye as described herein.

[0020] Alternatively, if the pH value of the washing liquid determined by the primary measurement is below a predetermined pH target value, at least a portion, in particular all, of the washing liquid is replaced with new washing liquid, in particular comprising fresh water. If the determined pH value is greater than the predetermined pH target value, the washing liquid is not replaced and the washing process continues.

[0021] The main measurement is carried out in particular during the initial water rinsing step and the washing liquid is replaced during the end phase of the initial water rinsing step or during the start phase of the following washing step.

[0022] e) Terminate the first washing process. This means that all steps a), b), c), d) and e) are carried out during the first washing process, ie during a single washing process. During a single washing process, the dishwasher is not unloaded.

[0023] The possibility and measurement of an additional amount of dishwashing detergent or alkalinity source has the advantage that the first amount does not have to be used in excess. Only the small first amount is added during the initial phase of the washing process (i.e., during step b) of the washing process). If the washing process is completed using only the small first amount of detergent, no additional amount is required and no detergent is wasted.

[0024] Advantageously, the method comprises an additional step f) performed between steps b) and c). A second amount of dishwashing detergent is added to the wash liquid before the main measurement is performed. In particular, the dishwashing detergent added in step f) contains a pH-sensitive dye that colors the wash liquid depending on the pH value of the wash liquid. The pH value of the wash liquid can be measured with a color sensor by measuring a parameter that depends on the transmission or reflection of the wash liquid in the visible electromagnetic spectrum at at least two, particularly at least three wavelengths. This measuring method is cost-effective because color sensors are cheap. Even if the first amount of dishwashing detergent already contains a pH-sensitive dye, adding the second amount freshens the color of the wash liquid and results in a more accurate pH measurement.

[0025] In particular, the second amount is predetermined and independent of any measurement.The second amount is only added to freshen the colour of the wash liquor and without substantially increasing the pH value of the wash liquor.

[0026] Advantageously, the second amount is added to the wash liquor not earlier than one minute, preferably not earlier than 30 seconds, more preferably not earlier than 15 seconds before step c).This ensures that the colour of the wash liquor does not fade before the main measurement, which would distort the measured pH value.

[0027] In a preferred embodiment, the second amount is added to the wash liquor no later than half a minute, preferably no later than 15 seconds, before step c). A certain minimum time span between adding the second amount and the main measurement is needed to ensure that the pH sensitive dye is mixed with the entire wash liquor by circulating it through the circulation system. If the main measurement is performed directly after adding the second amount, the wash liquor will not have uniform color and the pH measurement will be imprecise.

[0028] In particular, the additional amount depends on the difference between the predetermined pH target value and the pH value of the washing liquid determined in step c). After measuring the pH value of the washing liquid, it is determined whether to add an additional amount of dishwashing detergent or alkalinity source, and if so, it is determined to add an additional amount of dishwashing detergent or alkalinity source. For example, if the predetermined pH target value is 11 and the measured pH value is 7, dishwashing detergent or alkalinity source has to be added to the washing liquid to increase the pH value from 7 to 11. The amount of detergent or alkalinity source to be distributed depends on the composition of the detergent / alkalinity source and the total volume of the washing liquid. If the composition of the detergent / alkalinity source is unknown, a conservatively large amount of detergent is added to the washing liquid.

[0029] In particular, the predetermined pH target value depends on the temperature of the wash liquid.

[0030] In particular, the predetermined pH target value depends on the washing program. For example, a washing program for washing glass should have a lower pH target value (e.g., pH=10) than a strong washing program for washing kitchen equipment. Washing programs with lower pH values ​​for washing glass avoid or reduce glass corrosion.

[0031] Thus, the pH target value can be predetermined individually for each washing program and independently of the temperature of the wash liquid. Alternatively, the pH target value can be predetermined only in dependence on the temperature of the wash liquid or in dependence on both the washing program and the temperature.

[0032] Advantageously, the method comprises a further step g) carried out between steps a) and f), in particular between steps a) and b) or between steps b) and f). A pre-measurement for determining the pH value of the washing liquid is carried out, preferably not earlier than five minutes, preferably not earlier than two minutes, preferably not earlier than one minute before step f). In particular, the additional amount of detergent depends on the pH value of the washing liquid determined by the pre-measurement and the pH value of the washing liquid determined in step c).

[0033] In particular, the same measuring unit, in particular a color sensor, is used for both the pre-measurement and the main measurement.

[0034] The pre-measurement measures the color of the wash liquid before adding the second amount. The wash liquid can be stained by dyes from dishwashing soil, which would distort the primary measurement. To avoid this, a pre-measurement is performed and the result is used to correct the primary measurement. This is possible because the color spectra of the added detergent and dye are known.

[0035] In a preferred embodiment, dishwashing detergent is used in step d). Preferably, the composition of the dishwashing detergent used in step b) is the same as the composition of the detergent used in steps d) and / or f). If only a single detergent reservoir containing a single dishwashing detergent is provided in the dishwasher, this reduces costs. The first, second, and additional amounts are dispensed from the same detergent reservoir.

[0036] A further problem to be solved by the present invention is to provide a dishwasher with optimized dishwashing detergent consumption.

[0037] This problem is solved by a dishwasher according to claim 15. The dishwasher comprises a tub for loading dishwashing, a detergent reservoir for dispensing dishwashing detergent into the wash liquid and a circulation system for circulating the wash liquid. The dishwasher is adapted to carry out the method as described above.

[0038] According to a further aspect the invention relates to a dishwashing detergent for use in a dishwasher and in a method for operating a dishwasher as claimed and described herein, wherein the detergent comprises:

[0039] about 10% to about 20% by weight, preferably about 10% to about 15% by weight, of an alkalinity source selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal silicates, and mixtures thereof;

[0040] About 0.001 wt % to about 0.5 wt %, preferably about 0.01 wt % to about 0.1 wt % of a pH sensitive dye; and one or more functional additives, preferably selected from water softeners (e.g., builder or complexing agent), surfactants, anti-redeposition agents, enzymes (e.g., proteases, amylases), bleaching agents (e.g., sodium percarbonate), bleach activators, corrosion inhibitors (e.g., zinc acetate), and perfumes.

[0041] The dishwashing detergent of the present invention can be liquid, gel or solid, preferably gel or solid, more preferably solid. The solid can be powder, tablet or granule.

[0042] A typical cleaning process for removing food soil in a dishwasher often includes an initial water rinse step to remove water-soluble soil, a wash step with an aqueous solution containing dishwashing detergent, and a final fresh water rinse step. The dishwasher and dishwashing detergent according to the present invention enable precise dosing of dishwashing detergent in response to the amount of acidic soil present on the dishes during the wash step.

[0043] Standard dishwashing detergents typically contain from about 40% to about 50% by weight of an alkalinity source selected from alkali metal carbonates, alkali metal hydroxides, and alkali metal silicates. Advantageously, the amount of alkalinity source present in the dishwashing detergents claimed and described herein is significantly lower than in currently available dishwashing detergents. Thus, the dishwashing detergents of the present invention are more environmentally friendly and have lower manufacturing costs than currently available dishwashing detergents without impairing the quality of dishwashing.

[0044] As used herein, the term "alkali metal carbonate" includes alkali metal carbonates (eg, sodium carbonate, potassium carbonate), bicarbonates (eg, sodium bicarbonate, potassium bicarbonate), and sesquicarbonates (eg, sodium sesquicarbonate, potassium sesquicarbonate).

[0045] As is well known to the skilled person, the term "alkali metal hydroxide" includes sodium hydroxide, potassium hydroxide and lithium hydroxide.

[0046] As used herein, the term "alkali metal silicate" includes alkali metal silicates (eg, sodium silicate, potassium silicate), alkali metal disilicates (eg, sodium disilicate, potassium disilicate), and alkali metal metasilicates (eg, sodium metasilicate, potassium metasilicate).

[0047] Preferably, the source of alkalinity is a mixture of alkali metal carbonates and alkali metal silicates.

[0048] The pH-sensitive dye is preferably selected from malachite green, thymol blue, water blue (disodium hydroaminomethyl[[4-[(sulfonic acid phenyl)amino]phenyl][4-[(sulfonic acid phenyl)imino]cyclohexa-2,5-dien-1-ylidene]methyl]benzenesulfonate), neutral red (3-amino-7-dimethylamino-2-methylphenazine hydrochloride), phenolphthalein, thymolphthalein, alizarin (1,2-dihydroxyanthraquinone), Alizarin Yellow R (sodium 2-hydroxy-5-[(E)-(4-nitrophenyl)diazenyl]benzoate), Alizarin Red S (3,4-dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2-sulfonic acid), indigo carmine, bromothymol blue, Nile Blue A, hematoxylin and 2-naphthol orange. A particularly preferred pH sensitive dye is Alizarin Red S (3,4-dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2-sulfonic acid).

[0049] The pH sensitive dye preferably exhibits a color change at a pH between about 8 and about 12, more preferably between about 9 and about 11, and most preferably between about 9 and about 10.5.

[0050] Dishwashing detergents also contain one or more functional additives. The functional additives provide the desired properties and functions to the detergent. As used herein, the term "functional additive" includes materials that provide beneficial properties in a specific application when dispersed or dissolved in an aqueous solution. Suitable functional additives for dishwashing detergents are known in the art and can therefore be used in the context of the present invention.

[0051] The one or more functional additives are preferably selected from water softeners, surfactants, anti-redeposition agents, enzymes, bleaching agents, bleach activators, corrosion inhibitors and perfumes.

[0052] In a preferred embodiment according to the present invention, the detergent comprises:

[0053] At least about 45 wt. %, preferably at least about 50 wt. %, more preferably at least 60 wt. % water softener; and / or

[0054] At least about 10%, preferably at least about 12.5%, more preferably at least about 15.0%, by weight, of a bleaching agent; and / or

[0055] At least about 3 wt%, preferably at least about 4 wt%, more preferably at least about 5 wt% surfactant; and / or

[0056] • At least about 2 wt%, preferably at least about 3 wt%, more preferably at least 4 wt% enzyme.

[0057] When the water used in the aqueous liquid is very hard (e.g., more than 12° dH; 1° dH corresponds to 17.8 ppm of alkaline earth metal ions), dishwashing detergents containing at least 45% by weight, preferably at least about 50% by weight, and more preferably at least 60% by weight of a water softener are particularly useful. When the water used for dishwashing is soft or medium hard or an ion exchange column is used in the dishwasher, it is cost-effective and environmentally friendly to reduce the weight percentage of water softener in the dishwashing detergent (e.g., by a factor of 2, 3, or 4) and increase the weight percentage of other functional additives contained in the detergent.

[0058] Further advantageous embodiments are listed in the dependent claims and in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The present invention will be better understood from the following detailed description, and objects other than those set forth above will become apparent. Such description refers to the accompanying drawings, in which:

[0060] Figure 1 shows a dishwasher according to the present invention; and

[0061] Figure 2 A timeline showing a single dishwasher process.

[0062] Mode of invention

[0063] Figure 1 A household dishwasher is shown having a tub 1. Three baskets are arranged in the tub 1: a lower basket 2a, an upper basket 2b, and a cutlery basket 2c. The baskets can contain cutlery. Various spraying tools 3 are arranged in the tub 1: a lower spraying tool 3a, an intermediate spraying tool 3b (in the form of spray arms), and an upper spraying tool 3c for spraying washing liquid onto the cutlery. A circulation system with a circulation pump 4 circulates washing liquid from a bottom area 5 of the tub 1 via a circulation channel to the spraying tools 3. A heating device 6 is arranged in the circulation channel to heat the washing liquid to a certain temperature.

[0064] The dishwasher further comprises a discharge pump 7 for draining wash liquid from the bottom region 5 of the tub 1 and a fresh water inlet 8 for feeding fresh water into the dishwasher.

[0065] The various components of the dishwasher, particularly pumps 4 and 7 and heating device 6, are controlled by a control unit 9. Input and output devices 10 are connected to the control unit 9, allowing the user to input commands to the dishwasher and output information to the user. The control unit 9 contains various wash programs for operating the dishwasher. These include a speed program, a standard program, and an intensive program.

[0066] The dishwasher also includes a detergent reservoir 11 for dispensing dishwashing detergent into the tub 1. Detergent reservoir 11 can be filled with liquid or powdered detergent. A measuring unit 12 is arranged in the bottom area 5. Measuring unit 12 is a color sensor, specifically a multi-channel spectral color sensor, such as the AMS AS7341-11-Channel Spectral Color Sensor, which is an optical device for measuring a parameter that depends on the transmission or reflection of the wash liquid in the visible electromagnetic spectrum at eleven different wavelengths. The transmitted or reflected light is generated by a white LED with a broadband spectrum.

[0067] Alternatively, multi-color detection is possible through different color LEDs and broadband light sensors.

[0068] The method of operating the dishwasher will now be described. Figure 2 The timeline for a single dishwasher cycle is shown. At time 0, the user starts a standard dishwasher program, and the dishwasher cycle begins with an initial water rinse. Fresh water, or waste water from the final fresh water rinse of a previous wash cycle, is added to tub 1 via fresh water inlet 8, and pump 4 begins circulating fresh water through the circulation system. Sprayers 3a, 3b, and 3c spray fresh water onto the dishes arranged in baskets 2a, 2b, and 2c, removing water-soluble dirt.

[0069] After five minutes, at time 1, the circulating water is discharged by the discharge pump 7 and new clean water is added to the tub 1. The washing step begins. Clean water (hereinafter referred to as washing liquid) circulates in the circulation system and is heated by the heating device 6 to a certain temperature, for example 50°C.

[0070] At time 2 (which is three minutes after the wash liquid is added to tub 1), 10 g of powdered detergent is dispensed from detergent reservoir 11 to bottom area 5. This is the first amount of powdered detergent, which contains a small amount (e.g., about 0.001 wt% to about 0.5 wt%) of Alizarin Red S as a pH-sensitive dye. It is mixed into the wash liquid and washed for a while.

[0071] Ten minutes after dispensing the first amount of powder detergent, a series of several actions begins. Figure 2 The wash liquid is designated by reference numerals 3, 4, 5 and 6. At time 3, the measuring unit 12 measures the color of the wash liquid. This is a pre-measurement.

[0072] At time 4, the powder detergent of the second amount is distributed in the bottom area 5 from the detergent reservoir 11. Once again, the powder detergent comprises a small amount of Alizarin Red S (for example, about 0.001 % by weight - about 0.5 % by weight) as a pH sensitive dye. The second amount is about 3g of powder detergent. In each washing process, the powder detergent of the same amount is distributed at time 4 and the amount is independent of the predicted amount. The addition of the second amount is only intended to make the color of the washing liquid new.

[0073] At time 5, 30 seconds after time 4, a main measurement is performed by measuring unit 12. Both the pre-measurement and the main measurement generate signals at multiple different wavelengths. The difference in signal between the pre-measurement and the main measurement is calculated and the pH value is determined by least squares fitting of the difference. The fitting function is known from spectral calibration measurements of the components of the detergent.

[0074] At time 6, immediately after the pH value of the wash liquid has been determined by the primary measurement, if the pH value of the wash liquid is too low, an additional amount of powdered detergent or alkalinity source is dispensed into the wash liquid. For example, if a pH target value of 11 is required for effective washing, and the determined pH value is 7, an additional amount of, for example, 10 g is dispensed. The greater the difference between the pH target value and the determined pH value, the more additional detergent has to be dispensed into the wash liquid.

[0075] The washing process continues and at time 7, the washing liquid is drained by drain pump 7. New clean water is added to tub 1 and heated by heating device 4 for a final clean water rinse. A color sensor can also be used to determine the turbidity of the rinse water. Depending on the turbidity, the rinse step can be repeated.

[0076] At time 8, the circulating water is again discharged by the discharge pump 8. The drying process begins. The barrel 1 is cooled so that the moist air condenses on the cold walls of the barrel 1.

[0077] At time 9, the washing process ends.

[0078] Comments:

[0079] The first measurement for determining the pH value may have already been taken during the initial water rinse step. The amount of dishwashing detergent added during the initial phase of the main wash step may depend on the determined pH value. If a high pH value is determined during the initial water rinse step, only a small amount of dishwashing detergent may be added during the initial phase of the main wash step, and if a low pH value is determined, a larger amount may be added to the wash liquid.

Claims

1. A method of operating a dishwasher, wherein the dishwasher comprises - a bucket (1) for loading cutlery, - a detergent reservoir (11) for dispensing dishwashing detergent, - a circulation system for circulating the washing liquid, The method comprises the following steps a) starting the first washing process, b) adding a first amount of dishwashing detergent to the wash liquid, c) performing a primary measurement for determining the pH value of the wash liquid, d) adding an additional amount of dishwashing detergent or an alkalinity source to the wash liquid if the pH value of the wash liquid determined by the primary measurement is below a predetermined pH target value, or - replacing at least a portion of the washing liquid with new washing liquid, in particular comprising fresh water, if the pH value of the washing liquid determined by the primary measurement is below a predetermined pH target value, and e) terminating the first washing process.

2. The method according to claim 1, further comprising step f) performed between steps b) and c). f) adding a second amount of dishwashing detergent to the wash liquor.

3. The method according to claim 2, wherein the dishwashing detergent added in step f) comprises a pH sensitive dye, The pH of the wash liquor is preferably determined by measuring the colour of the wash liquor which has been coloured by the pH sensitive dye.

4. A method according to claim 2 or 3, wherein the second amount is predetermined and independent of any measurement.

5. The method according to any one of claims 2 to 4, wherein the second amount is added to the wash liquor not earlier than one minute, preferably not earlier than 30 seconds, more preferably not earlier than 15 seconds before step c).

6. The method according to any one of claims 2 to 5, wherein the second amount is added to the wash liquor not later than 30 seconds, preferably not later than 15 seconds before step c).

7. A method according to any one of the preceding claims, wherein the additional amount is dependent on the difference between the predetermined pH target value and the pH value of the wash liquor determined in step c).

8. The method according to any of the preceding claims, wherein the predetermined pH target value depends on the washing program or on the temperature of the washing liquid.

9. The method according to claim 2 and according to one of the preceding claims, further comprising a step g) carried out between steps a) and f), in particular between steps a) and b) or between steps b) and f), g) performing a pre-measurement of said washing liquid, The pre-measurement is preferably performed no earlier than five minutes, preferably no earlier than two minutes, more preferably no earlier than one minute before step f).

10. The method of claim 9, wherein the additional amount depends on the predicted amount.

11. A method according to claim 9 or 10, wherein the additional amount depends on the difference or quotient between the predicted amount and the primary measurement.

12. The method according to any one of the preceding claims, wherein the dishwashing detergent added in step b) and the dishwashing detergent added in step d) have the same composition.

13. The method according to claim 2 and according to one of the preceding claims, wherein the dishwashing detergent added in step b), the dishwashing detergent added in step f) and the dishwashing detergent added in step d) have the same composition.

14. The method according to claim 1 , wherein the washing process further comprises an initial water rinse step and the first measurement for determining the pH value is carried out during the initial water rinse step, in particular at the latest two minutes, in particular at the latest one minute after the start of the washing process.

15. Method according to any of the preceding claims, wherein step c) is carried out during an initial water rinsing step and the washing liquid is replaced according to step d) during the end phase of the initial water rinsing step or during the start phase of a subsequent washing step.

16. A dishwasher for washing dishes, comprising - a bucket (1) for loading said tableware, - a detergent reservoir (11) for dispensing dishwashing detergent into the wash liquid, - a circulation system for circulating the washing liquid, - a measuring unit (12) for determining the pH value of the washing liquid, Wherein the dishwasher is adapted to carry out the method according to any one of the preceding claims.

17. The dishwasher according to claim 16, wherein the measuring unit (12) is an optical device for measuring a parameter that depends on transmission or reflection in the visible electromagnetic spectral range at at least two, in particular at least three wavelengths.

18. Dishwashing detergent for use in a method according to any one of claims 1 to 15, or for use in a dishwasher according to claim 16 or 17, wherein the detergent comprises: about 10% to about 20% by weight, preferably about 10% to about 15% by weight, of an alkalinity source selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal silicates, and mixtures thereof; About 0.001 wt% to about 0.5 wt%, preferably about 0.01 wt% to about 0.1 wt% of a pH sensitive dye; and One or more functional additives, preferably selected from water softeners, surfactants, anti-redeposition agents, enzymes, bleaching agents, bleach activators, corrosion inhibitors and perfumes, wherein the weight % is based on the total weight of the detergent.

19. The detergent according to claim 18, wherein the detergent is a gel or a solid, preferably a solid.

20. The detergent according to claim 18 or 19, wherein the pH sensitive dye is selected from malachite green, thymol blue, water-soluble blue, neutral red, phenolphthalein, thymolphthalein, alizarin, alizarin yellow R, alizarin red S, indigo carmine, bromothymol blue, Nile blue A, hematoxylin and 2-naphthol orange.

21. The detergent according to any one of claims 18 to 20, wherein the detergent comprises: At least about 45 wt. %, preferably at least about 50 wt. %, more preferably at least 60 wt. % water softener; and / or At least about 10%, preferably at least about 12.5%, more preferably at least about 15.0%, by weight, of a bleaching agent; and / or At least about 3 wt%, preferably at least about 4 wt%, more preferably at least about 5 wt% surfactant; and / or • At least about 2 wt%, preferably at least about 3 wt%, more preferably at least 4 wt% enzyme.

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