JP3857838B2

JP3857838B2 - Insulated rice cooking method and rice cooker

Info

Publication number: JP3857838B2
Application number: JP24156299A
Authority: JP
Inventors: 真千子阿部; 崇史大宅; 篤史小室; 孝博河内
Original assignee: Osaka Gas Co Ltd; Rinnai Corp
Current assignee: Osaka Gas Co Ltd; Rinnai Corp
Priority date: 1999-08-27
Filing date: 1999-08-27
Publication date: 2006-12-13
Anticipated expiration: 2019-08-27
Also published as: JP2001061651A; KR20010066965A; KR100368451B1

Description

【０００１】
【発明の属する技術分野】
本発明は、米飯の保温方法および炊飯器の技術分野に属し、例えば、保温が開始されて既に１回、加熱器による再加熱が行われた後に長時間保温機能がセットされた場合であっても、１８時間、２４時間等の長時間にわたり米飯中の好熱性バチルス菌の増殖を抑制し黄変や異臭等の発生を防止するものである。
【０００２】
【従来の技術】
最近の炊飯器は、炊飯時に炊飯釜を加熱する加熱器とは別に、炊き上がった米飯を炊飯釜内で一定の温度に保温して長時間にわたり温かい米飯を提供できるように電気ヒータやハロゲンランプ等による保温加熱器を備える。そして、近年、ライフスタイルの多様性から、このような炊飯器として、いつでも美味しい米飯が食べられるように１８時間、さらには２４時間の長時間保温機能が求められるようになってきた。これまでの知見から、美味しく感じる米飯の最適温度は、炊き上がり直後の９０℃以上であるが、保温温度が高ければ高い程、米飯の乾燥が顕著に認められるため、通常は保温温度を７０℃程度まで下げている。
【０００３】
【発明が解決しようとする課題】
しかしながら、前記保温加熱器によって米飯の保温温度を７０℃程度に保っていると、米に混入している好熱菌（好熱性バチルス菌）が増殖し、保温開始から１４〜１５時間後には前記好熱性バチルス菌の増殖によって米飯から異臭を放ってくる。この好熱性バチルス菌は、炊飯温度の約１００℃では死滅せず、炊飯器の保温温度である６０℃〜７０℃で増殖する。また、この好熱性バチルス菌は、胞子型と栄養型とが存在し、８０℃以上にすると栄養型の形態にある好熱性バチルス菌は減少するが、胞子型として生き残る。そのため、保温温度が６０〜７０℃になると、この胞子が再び発芽し栄養型となって増殖する。しかも、この好熱性バチルス菌は、増殖するにつれて生菌数の約１０％という高い割合で胞子型を順次形成する。また、栄養型の好熱性バチルス菌が米飯中で増殖し、その生菌数が約１０⁷個／ｇ以上となると異臭を放ってくる。そのため、炊飯終了後の長時間にわたり米飯を保温するには前記好熱性バチルス菌の増殖を抑制するような温度管理が必要であった。
【０００４】
特開平９−２７６１３４号公報においては、米飯の保温を開始してから約５時間後に炊飯器の加熱器を作動させ、炊飯釜内の米飯を８０℃以上に再加熱することにより、栄養型にある好熱性バチルス菌の増殖を抑制させる保温方法が提案された。これは、米に混入していた前記好熱性バチルス菌が、炊飯直後に約７０℃で保温を開始した場合に約５時間経過後から増殖が始まることに対応したものである。このものによると、例えば、夕食で余った米飯を翌日の朝食に食する場合のように炊飯終了後から１４〜１５時間は、米飯中の好熱性バチルス菌の増殖を抑え、美味しい米飯のまま保温できた。
【０００５】
ところが、このものでは、炊飯終了後から１８時間、あるいは、２４時間の長時間保温を考えると、好熱性バチルス菌の増殖による異臭や黄変の防止が不十分なため、同公報には、米飯の保温を開始してから約５時間毎に炊飯器の加熱器を作動させる保温方法も提案されている。これによると、保温米飯中の好熱性バチルス菌が増殖し始める時点で再加熱するから、米飯の長時間保温において好熱性バチルス菌の増殖が抑制されて米飯からの異臭や黄変を防止させることができた。
【０００６】
前記のような数回米飯を再加熱する長時間保温機能は、一般に、炊飯開始前に長時間保温スイッチを入れることによりセットされるが、遅くとも保温を開始するまでにセットされてあれば、この長時間保温機能が働き出す保温動作と同時にタイマーを作動させ、このタイマーにより時間を計測して保温開始時点から所定時間経過した後に加熱器が作動されるものである。
【０００７】
しかしながら、炊飯終了後、保温が開始されてから所定時間後に１回再加熱する保温機能を有するものにおいて、既に前記再加熱が行われた後に、長時間保温スイッチが入れられる場合がある。例えば、食事した後に多くの米飯が残ってしまったり、炊飯したもののしばらくの間は食べないという状況になった場合において、保温が開始されて既に１回、加熱器による再加熱が行われた後に前記長時間保温スイッチが入れられることがある。このような場合は、長時間保温スイッチが入れられた時点で長時間保温機能が働き出すから、この長時間保温スイッチが入った時点からタイマーが駆動されて所定時間経過した後に前記加熱器を作動させることとなる。そのため、２回目の再加熱は、１回目の再加熱が行われてから本来予定された２回目の再加熱時間よりかなりオーバーした時刻で加熱器が作動することとなるから、すでに米飯中の好熱性バチルス菌の増殖が進行し、最悪の場合、１８時間目、２４時間目の時点で異臭を放つ程に増殖していることがある。
【０００８】
本発明は、『炊飯時に炊飯釜を加熱する炊飯加熱器と、保温時に前記炊飯釜を加熱する保温加熱器とを具備』するものにおいて、保温が開始されて既に１回、加熱器による再加熱が行われた後に、長時間保温機能がセットされた場合であっても、長時間にわたり美味しい米飯が食べられるように保温することをその課題とする。
【０００９】
【課題を解決するための手段】
前記課題を解決するために講じた技術的手段は、次のようである。
【００１０】
米飯の保温方法として、『米飯の炊飯終了後、前記保温加熱器によって米飯を約７０℃に保温する一方、前記炊飯加熱器を、前記保温を開始してから所定時間後の再加熱時刻に一時的に作動させ、米飯を８０℃〜１１０℃の温度範囲内で再加熱する米飯の保温方法において、
前記再加熱を数回行わせる長時間保温スイッチを入れた時間が、前記再加熱を行ってから約４時間経過以前であれば２回目以後の再加熱を前記１回目の再加熱から約４時間毎に行い、前記再加熱を行ってから約４時間経過以後であれば２回目の再加熱を直ちに行い、３回目以後の再加熱を前記２回目の再加熱から約４時間毎に行うことを特徴とする。』
前記技術的手段は、次のように作用する。
【００１１】
前記再加熱を数回行わせる長時間保温スイッチを入れた時間が、１回目の再加熱を行ってから約４時間経過以前であれば２回目以後の再加熱を前記１回目の再加熱から約４時間毎に行う。これにより、２回目以後の再加熱は、前記長時間保温スイッチを入れてから約４時間後に行われることなく、１回目の再加熱を行ってから約４時間毎に行われるから、１回の再加熱でも生存している胞子型の好熱性バチルス菌がその後次々と発芽、増殖する時間帯にあわせて再加熱されるため、２４時間にわたり栄養型にある好熱性バチルス菌の生菌数を効果的に減少させることができる（図４参照）。
【００１２】
また、前記長時間保温スイッチを入れた時間が、１回目の再加熱を行ってから約４時間経過以後であれば２回目の再加熱を直ちに行い、３回目以後の再加熱を前記２回目の再加熱から約４時間毎に行う。これにより、２回目の再加熱は、１回の再加熱でも生存している胞子型の好熱性バチルス菌がその後次々と発芽、増殖する時間帯から大幅に遅れることなく前記時間帯に近い時刻で再加熱することができる。
【００１３】
このように、１回目の再加熱が行われた後において、長時間保温スイッチを入れた時間に関係なく、１回の再加熱でも生存している胞子型の好熱性バチルス菌がその後次々と発芽、増殖する時間帯、あるいは、この時間帯に近い時刻で再加熱するから、当該好熱性バチルス菌に対する増殖抑制効果が大きい。
【００１４】
また、前記炊飯加熱器の再加熱時における加熱温度と加熱時間との関係は、炊飯釜内の米飯を８０℃〜１１０℃の温度範囲内で１秒〜５分間とする。これは、胞子型にある好熱性バチルス菌は、炊飯温度の１００℃、約２０分の加熱でもその数を維持しているが、異臭や黄変の原因となる栄養型の好熱性バチルス菌は、その加熱温度が８０℃以上になると数が減少するから、米飯中から異臭や黄変をもたらす好熱性バチルス菌の増殖を確実に抑制することができる。また、米飯の加熱温度の上限を１１０℃以下とするから、米飯の乾燥を抑制でき、特に炊飯釜内底部の米飯がぱりぱりに乾燥し堅くなってしまうようなこともない。さらに、加熱時間を１秒〜５分間とするのは、１秒間の加熱でも前記栄養型の好熱性バチルス菌を減少させることができる一方、５分間以内の加熱であれば米飯の乾燥を進めることもない。そして、炊飯加熱器の作動を停止するとほぼ１時間半以内に保温温度の約７０℃まで低下する（図３参照）。このことから、米飯が乾燥する程の余分な熱が加わらずに好熱性バチルス菌へのダメージに必要な加熱ができる。
【００１５】
そして、炊飯器として、『前記保温加熱器を、炊飯終了後の米飯を約７０℃に保温するように作動制御する保温加熱器制御部と、
前記炊飯加熱器を、前記保温加熱器による保温を開始してから所定時間後の再加熱時刻に一時的に作動させ、米飯を８０℃〜１１０℃の温度範囲内で再加熱するように作動制御する炊飯加熱器制御部と、
前記炊飯加熱器による前記再加熱動作を数回行わせるための長時間保温スイッチと、
１回目の再加熱時刻を記憶させる記憶部と、
前記長時間保温スイッチを入れた時間が前記記憶部における炊飯終了時刻から起算して前記再加熱を行ってから約４時間経過以前であれば２回目以後の再加熱を前記１回目の再加熱から約４時間毎に行わせ、前記再加熱を行ってから約４時間経過以後であれば２回目の再加熱を直ちに行い、３回目以後の再加熱を前記２回目の再加熱から約４時間毎に行わせる保温制御部とを備えた』ものでは、米飯の保温時に前記保温制御部によって炊飯加熱器を作動制御することにより、前記保温方法と同様の作用を奏する。
【００１６】
前記技術的手段において、『前記再加熱時刻は、保温を開始してから６〜８時間後である』ものでは、１回目の再加熱を、米飯の保温時に黄変や異臭を発生させる原因菌の好熱性バチルス菌が、米飯の保温に適した７０℃くらいで発芽、増殖し、保温を開始してからこの好熱性バチルス菌の増殖が最も盛んになる６〜８時間（図４参照）の時間帯にあわせたから、この１回目の再加熱における当該好熱性バチルス菌に対する増殖抑制効果が大きい。
【００１７】
そして、前記炊飯器において、『前記再加熱時刻は、保温を開始してから６〜８時間後である』ものでも、この保温方法と同様の作用を奏する。
【００１８】
【発明の効果】
本発明によれば、保温が開始されて既に１回、加熱器による再加熱が行われた後に長時間保温機能がセットされた場合でも、１回の再加熱でも生存している胞子型の好熱性バチルス菌がその後次々と発芽、増殖する時間帯、あるいは、この時間帯に近い時刻で再加熱するから、米飯中の好熱性バチルス菌の増殖を効果的に抑制することができ、その結果、炊飯終了後長時間にわたり美味しい米飯が食べられるようになる。
【００１９】
【発明の実施の形態】
以下に、本発明の実施の形態について図面を参照しながら説明する。
【００２０】
図１は、本発明の実施の形態によるガス炊飯器の構成を示す断面図である。図１に示すように、実施の形態によるガス炊飯器１は、米等を収容して加熱調理する炊飯釜２と、この炊飯釜２を収容する外容器３と、前記外容器３に開閉可能に取付けられた蓋体４と、前記炊飯釜２の底部下方に設けられる炊飯加熱器としてのガス加熱器５と、このガス加熱器５を構成するガスバーナ６を囲むようにして設けられる電気ヒータ７と、炊飯釜２の底面に接触するように設けられた温度センサ８とを備える。また、前記ガスバーナ６の近傍には、点火装置９が配置されており、上部には炊飯を実行させる炊飯スイッチ１６と、炊飯終了後に前記ガス加熱器５による再加熱動作を数回行わせるための長時間保温スイッチ１７とが配置されている。また、このガス炊飯器１は、保温時間を計測するためのタイマーを備えている（図示せず）。
【００２１】
前記ガス加熱器５及び電気ヒータ７は、マイクロコンピュータを備える制御装置１０によって作動が制御される。この制御装置１０は、炊飯制御部１１と、保温加熱器制御部１２と、ガス加熱器制御部１３と、炊飯終了後の１回目の再加熱時刻を記憶するメモリー１４と、保温制御部１５とを備える。
【００２２】
前記炊飯制御部１１によって、設定された炊飯パターンに従って前記ガス加熱器５の作動を制御して、点火時期、消火時期、火力等をコントロールしながら炊飯動作を行う。
【００２３】
前記保温加熱器制御部１２によって、炊飯動作終了後、前記電気ヒータ７を作動制御して、炊飯釜２内を一定温度に保温制御する。本実施の形態においては、保温温度を約７０℃に設定している。
【００２４】
前記ガス加熱器制御部１３によって、前記ガス加熱器５を、前記電気ヒータ７による保温を開始してから所定時間後の再加熱時刻に一時的に作動させ、米飯を８０℃〜１１０℃の温度範囲内で再加熱するように作動制御する。本実施の形態においては、前記所定時間を７時間に設定している。
【００２５】
前記保温制御部１５によって、前記長時間保温スイッチを入れた時間が前記メモリー１４における炊飯終了時刻から起算して前記再加熱を行ってから約４時間経過以前であれば２回目以後の再加熱を前記１回目の再加熱から約４時間毎に行わせ、前記再加熱を行ってから約４時間経過以後であれば２回目の再加熱を直ちに行い、３回目以後の再加熱を前記２回目の再加熱から約４時間毎に行わせる。
【００２６】
なお、本実施の形態では、保温加熱器として、前記電気ヒータ７を用いるが、ハロゲンランプ等他熱源を採用しても良い。
【００２７】
次に、本実施の形態によるガス炊飯器１の保温動作を説明する。
【００２８】
図２は、保温動作開始後の制御の流れを示したフローチャートである。図３は、炊飯釜２の再加熱を３分間行った場合の温度変化を示し、実線は炊飯釜２内の米飯下部の温度変化、鎖線は炊飯釜２内の米飯上部の温度変化をそれぞれ示している。図４は、再加熱による好熱性バチルス菌の生菌数（個／ｇ）の変化を示している。
【００２９】
本実施の形態においては、炊飯動作を行う際に、炊飯釜２内が所定の温度に達する加熱時間等から米量を検出し、これを保温動作時の情報として利用する。この米量検出は、前記制御装置１０の炊飯制御部１１が行う。まず、炊飯動作を終了した後、保温動作に入る。この保温は、前記保温加熱器制御部１２において温度センサ８によって炊飯釜２の底部の温度を検出しながら電気ヒータ７に間欠的に通電して、炊飯釜２内を約７０℃に保持する。なお、この電気ヒータ７による保温は、以下に説明するガス加熱器５の動作中においても有効に働いている。
【００３０】
図２に示すように、保温動作に入ると、保温制御部１５において保温を開始してから７時間が経過したか否かを監視する（Ｓ１０１）。７時間が経過すると、このときの時刻を１回目の再加熱時刻として前記制御装置１０内のメモリー１４に記憶させ（Ｓ１０２）、続いて、保温制御部１５にてガス加熱器５を作動させて炊飯釜２の温度を急激に上昇させる。このとき、本実施の形態においては、まず、炊飯制御部１１が炊飯動作で検出した米量に応じて、ガス加熱器制御部１３によって加熱時間を決定する（Ｓ１０３，Ｓ１０４）。その後、ガス加熱器５を作動させて（Ｓ１０５，Ｓ１０６，Ｓ１０７）、米量「小」の場合には１分間加熱し（Ｓ１０８）、米量「中」の場合には２分間加熱し（Ｓ１０９）、米量「大」の場合には３分間加熱するように制御する（Ｓ１１０）。本実施の形態では、この米量が「大」の場合を説明する。すると、米飯温度は、米飯上部が約８５℃で、米飯下部（炊飯釜２の底付近）が約１００℃となり（図３の７時間目参照）、炊飯釜２内の米飯の温度は８０℃〜１１０℃の範囲になる。このときの米飯中における好熱性バチルス菌の生菌数は、再加熱直前に約１０⁴個／ｇであったものが、再加熱により１００個／ｇ以下に減少する（図４の７時間目参照）。
【００３１】
なお、米量「小」および「中」の場合にも、各々の加熱時間によって米飯の温度が８０℃〜１１０℃の範囲内となるように構成している。このように保温時の米飯の温度を８０℃〜１１０℃の範囲内とするのは、１１０℃を超えると、炊飯釜２内の米飯の下部の方ではぱりぱりに乾燥し、一方、８０℃未満であれば、米飯中に混入し異臭や黄変の原因となる栄養型の好熱性バチルス菌を減少させることができない。すなわち、好熱性バチルス菌の生菌数を減少させて、増殖の停止時間を長くするには、米飯の加熱温度を高めるとともに、その加熱温度に保持する時間を長く設定するのが望ましい。しかしながら、米飯の加熱温度が高すぎたり、加熱時間が長すぎると、米飯の乾燥を早め、却って食味を低下させることになる。一方、米飯からの異臭や黄変を防止するには、栄養型にある好熱性バチルス菌の生菌数を少なくとも１０⁶個／ｇ以下に減少させれば足りる。したがって、米飯の温度を８０℃まで上昇させて、前記好熱性バチルス菌の生菌数を減少させれば、米飯からの異臭や黄変を停止することができる。また、加熱時間も１秒〜５分間で好熱性バチルス菌の生菌数を減少させることが期待できる。特に本実施の形態の如くガス加熱器５によると、電気加熱に対するガス加熱の特性として、ガス火によると短時間で設定温度に昇温することができ、例えば、３分間の加熱によって最も熱の加わりやすい炊飯釜内底部の米飯で約１００℃まで昇温し、熱の加わりにくい米飯上部で約８５℃まで昇温する（図３参照）。これにより、米飯中から異臭や黄変をもたらす好熱性バチルス菌の増殖を抑制することができる。このことから、米飯が乾燥する程の余分な熱が加わらずに好熱性バチルス菌へのダメージに必要な加熱ができる。
【００３２】
そして、前記ガス加熱器５による再加熱が所定時間（本例では、３分間）経過すると（Ｓ１１０）、ガスバーナ６を消火してガス加熱器５の作動を終了させ（Ｓ１１１）、電気ヒータ７による通常の保温動作に戻る。すると、ガス加熱器５による再加熱を終了して約１時間半経過後の８時間半経過時点には炊飯釜２内の米飯が約７０℃に保持される。
【００３３】
次に、２回目以後の再加熱動作を説明する。
【００３４】
前記１回目の再加熱が行われた後に、再加熱を数回行わせる長時間保温スイッチ１７が入れられると（Ｓ１１２）、前記メモリー１４において記憶させた１回目の再加熱時刻から起算して４時間が経過したか否かを判別する（Ｓ１１３）。まだ４時間が経過していない場合は前記ステップＳ１１３の監視動作を繰り返し、４時間が経過するまで待機状態が続く。そして、この待機状態を続けながら１回目の再加熱を行ってから４時間が経過するか、前記ステップＳ１１２で長時間保温スイッチがＯＮされた時点で既に４時間が経過していると、タイマーを駆動させた後（Ｓ１１４）、保温制御部１５にてガス加熱器５を作動させて炊飯釜２の温度を急激に上昇させる（Ｓ１１５）。このときの加熱時間として、前記１回目の再加熱のときと同じく３分間作動させる（Ｓ１１６）。本例では、前記１回目の再加熱が保温を開始してから７時間目に行われた場合とし、長時間保温スイッチ１７は１回目の再加熱を行ってから４時間経過以前にＯＮされたとする。よって、この２回目の再加熱は保温を開始してから１１時間目に行われたこととなる。すると、図３中、１１時間目の米飯温度を見ると、７時間経過時点の１回目の再加熱のときと同様に、炊飯釜２内の米飯は、８０℃〜１１０℃の温度範囲内に昇温される。このとき、米飯中の好熱性バチルス菌は、図４中の１１時間目付近を見ると、１回目の再加熱終了後から徐々に増殖し、この２回目の再加熱直前には１０³個／ｇ近くに増えていたが、再加熱によって再び１０個／ｇ以下に減少したことが判る。この２回目の再加熱が所定時間（本例では３分間）経過すると（Ｓ１１６）、ガス加熱器５の作動を終了させ（Ｓ１１７）、通常の保温動作に戻る。
【００３５】
次に、前記再加熱が保温を開始してから３回実行されたか否かを判別する（Ｓ１１８）。つまり、本実施の形態では、炊飯終了後、保温を開始してからガス加熱器５による再加熱を３回行うように設定されている。そして、現時点では、再加熱は２回しか行っていないので、この場合、前記ステップＳ１１３の前に戻される（Ｓ１１８）。すると、３回目の再加熱として、前記タイマーで計測している時間を監視し、２回目の再加熱を開始してから４時間が経過すると（Ｓ１１３）、タイマーをリセットしてからＯＮした後（Ｓ１１４）、再びガス加熱器５を３分間作動させて炊飯釜２の温度を急激に上昇させる（Ｓ１１５，Ｓ１１６）。この３回目の再加熱は、前記２回目の再加熱が保温を開始してから１１時間目に行われるので、保温を開始してから１５時間目となる。すると、図３中、７時間経過時点の１回目の再加熱、それから４時間後の１１時間経過時点の２回目の再加熱のときと同様に、炊飯釜２内の米飯は、８０℃〜１１０℃の温度範囲内に昇温される。これにより、米飯中の好熱性バチルス菌は、図４中、１５時間目付近を見ると、２回目の再加熱終了後から徐々に増殖し、この３回目の再加熱直前には１０²個／ｇ近くに増えていたが、再加熱によって１０個／ｇ以下に減少したことが判る。そして、この３回目の再加熱が所定時間（本例では３分間）経過すると（Ｓ１１６）、ガス加熱器５の作動を終了させる（Ｓ１１７）。
【００３６】
その後、この３回目の再加熱が実行された後は（Ｓ１１８）、前記１回目の再加熱時刻をメモリー１４からクリアし（Ｓ１１９）、電気ヒータ７による通常の保温動作に戻る。
【００３７】
このようにして炊飯終了後２４時間保温した米飯の２４時間目のものについて評価したところ、堅くなっていたり、炊飯釜２の底にくっつく等の不具合も見られなかった。しかも、米飯のにおい、色、味のいずれも特に気にかかる点はなかった。この点は好熱性バチルス菌の生菌数が約１０⁷個／ｇ以上になると異臭等を放つが、本例の場合、図４中の２４時間目を見ると、１０個／ｇ程度であったことからも米飯の品質保持が裏付けられる。しかも、最後の再加熱である３回目の加熱時点から２４時間目までは２回目、３回目の時間間隔である４時間以上の間隔があるが、前記３回の再加熱によって米飯中における全好熱性バチルス菌の個数が効果的に減少するから、２４時間目の時点においても好熱性バチルス菌が異臭等を放つ程の個数に増殖していないことが判る。
【００３８】
以上のように、本実施の形態においては、保温が開始されて既に１回、加熱器による再加熱が行われた後に長時間保温機能がセットされた場合でも、米飯中の好熱性バチルス菌の増殖を効果的に抑制することができ、その結果、炊飯終了後２４時間にわたり美味しい米飯が食べられるようになる。すなわち、米飯中では好熱性バチルス菌の増殖に伴ってその生菌数の約１０％が胞子型となって存在しており、１回の再加熱の後、この胞子型のものが次々と発芽して栄養型となる時間帯が約４時間後であることから、２回目と、３回目の再加熱の時間間隔を４時間毎とすることにより、好熱性バチルス菌の急激な増殖を抑制することができる。本実施の形態では、長時間保温スイッチ１７が１回目の再加熱を行ってからまだ４時間経過していないときにＯＮされた場合を示すが、すでに４時間経過していた場合であっても直ちに前記ガス加熱器５による再加熱を行うから、再加熱は、米飯中の好熱性バチルス菌の増殖が最も盛んになる時間帯より大きく遅れることなく前記時間帯に近い時刻で再加熱することができる。
【００３９】
また、保温中のガス加熱器５による再加熱は、２４時間保温において３回で済み（７時間後、１１時間後、１５時間後）、５時間毎に４回の再加熱が行われる従来方法（特開平９−２７６１３４号公報）と比べ、米飯の乾燥を防止でき、且つ、再加熱１回分の省エネを図ることができる。
【００４０】
なお、前記実施の形態においては、ガス加熱器５による再加熱時間として、１分間、２分間または３分間とするが、１秒から５分間の間で適宜に決定しても良い。また、１回目の再加熱として、保温を開始してから７時間後をこの１回目の再加熱時刻とするが、６〜８時間後の間で適宜に決定しても良い。
【００４１】
また、前述の如く再加熱時間を規定しているが、米量により炊飯釜２底の米飯が焦げるような場合もあり得るので、再加熱時間内に設定温度（炊飯消火温度、または炊飯消火温度より低い温度たとえば１１０℃）に達した場合は設定温度を優先して、加熱動作を終了させれば良い。
【００４２】
また、米量を大中小の３段階に分けてガス加熱器５の加熱時間を選択するように制御したが、炊飯器の容量、米量、ガス加熱器の容量等に応じてさらに細かく分けたり、あるいは、米量大と小の２段階に分ける等、適宜に決定しても良い。
【００４３】
また、前記のような米量によってガス加熱器５の加熱時間を選択することなく、炊飯釜２内下部の米飯温度が１１０℃に達した時点でガス加熱器５の動作が終了するように制御しても良い。これは、下部の米飯温度が１１０℃に達していれば上部の米飯温度も８０℃以上に達していると推定され、炊飯釜２内の米飯温度としては、全体として８０℃〜１１０℃の範囲内に収まるからである。
【００４４】
また、前記再加熱は、ガス加熱器５を用いているが、この再加熱用に電気ヒータを使用しても良く、この場合、通常保温を行わせていた前記電気ヒータ７と兼用しても良いし、これとは別個に専用の電気ヒータを備え付けても良い。さらには、本例の如くガス炊飯器ではなく、電気炊飯器において適用しても良く、この電気炊飯器の場合は炊飯を行わせる電気ヒータや通常保温を行わせる電気ヒータを前記再加熱に兼用しても良いし、また、別個に再加熱専用の電気ヒータを備え付けても良い。ただし、電気加熱よれば、ガス加熱に比べて昇温速度や米飯に対する熱の廻りの点でやや劣るものの米飯中の好熱性バチルス菌の増殖を抑えるには十分である。
【００４５】
一方、２回目、３回目の再加熱時間を１回目と同じ再加熱時間となるように設定しているが、１回目の再加熱のときの炊飯釜２底における最高温度を制御装置１０内等のメモリに一時記憶し、２回目、３回目の再加熱は、この一時記憶した最高温度に達したときに終了するように制御しても良い。
【図面の簡単な説明】
【図１】実施の形態のガス炊飯器の構成を示す断面図である。
【図２】実施の形態における保温動作開始後の制御の流れを示したフローチャートである。
【図３】実施の形態における炊飯釜２の再加熱を３分間行う場合の温度変化を示し、実線は炊飯釜２内の米飯下部の温度変化、鎖線は炊飯釜２内の米飯上部の温度変化をそれぞれ示している。
【図４】実施の形態における再加熱による好熱性バチルス菌の生菌数（個／ｇ）の変化を示している。
【符号の説明】
１炊飯器
２炊飯釜
３外容器
４蓋体
５ガス加熱器
６ガスバーナ
７電気ヒータ
８温度センサ
９点火装置
１０制御装置
１１炊飯制御部
１２保温加熱器制御部
１３ガス加熱器制御部
１４メモリー
１５保温制御部
１６炊飯スイッチ
１７長時間保温スイッチ[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the technical field of cooked rice warming methods and rice cookers, for example, when the warming function has been set for a long time after the warming has been started and reheating has already been performed once by the heater. In addition, the growth of thermophilic Bacillus in the cooked rice is suppressed over a long period of time such as 18 hours and 24 hours, thereby preventing yellowing and off-flavors.
[0002]
[Prior art]
In recent rice cookers, apart from the heater that heats the rice cooker during rice cooking, the cooked rice is kept at a certain temperature in the rice cooker to provide warm rice for a long time. Equipped with a warming heater. In recent years, due to the diversity of lifestyles, such rice cookers have been required to have a long-time heat retention function of 18 hours or even 24 hours so that delicious rice can be eaten at any time. From the knowledge so far, the optimal temperature of cooked rice to be delicious is 90 ° C or more immediately after cooking. However, the higher the heat retention temperature, the more noticeably dry rice is cooked. It is lowered to the extent.
[0003]
[Problems to be solved by the invention]
However, when the temperature of the cooked rice is kept at about 70 ° C. by the heat retaining heater, thermophilic bacteria (thermophilic Bacillus) mixed in the rice grow and the temperature is 14 to 15 hours after the start of heat retention. A strange odor is emitted from the cooked rice by the growth of thermophilic Bacillus. This thermophilic Bacillus is not killed at a cooking temperature of about 100 ° C., but grows at a temperature of 60 ° C. to 70 ° C., which is the heat retaining temperature of the rice cooker. Moreover, this thermophilic Bacillus bacterium exists in a spore type and a vegetative type. When the thermophilic Bacillus bacterium is at 80 ° C. or higher, the thermophilic Bacillus bacterium in the form of the vegetative type decreases, but survives as a spore type. Therefore, when the heat retention temperature reaches 60 to 70 ° C., these spores germinate again and grow as a vegetative type. Moreover, the thermophilic Bacillus bacteria sequentially form spores at a high rate of about 10% of the number of viable bacteria as they grow. In addition, vegetative thermophilic Bacillus bacteria grow in the cooked rice and the number of viable bacteria is about 10 ⁷ When it becomes more than 1 piece / g, a strange odor is emitted. Therefore, temperature control is required to keep the cooked rice warm for a long time after cooking, so as to suppress the growth of the thermophilic Bacillus.
[0004]
In Japanese Patent Application Laid-Open No. 9-276134, the rice cooker heater is activated about 5 hours after the start of the heat insulation of the cooked rice, and the cooked rice in the rice cooker is reheated to 80 ° C. or higher to make it a nutritional type. A heat-retaining method was proposed that inhibits the growth of certain thermophilic Bacillus bacteria. This corresponds to the fact that the thermophilic Bacillus bacteria mixed in the rice starts to grow after about 5 hours when the heat retention is started at about 70 ° C. immediately after cooking. According to this, for example, as in the case of eating the surplus rice at dinner for breakfast the next day, the growth of thermophilic Bacillus bacteria in the cooked rice is suppressed for 14 to 15 hours after cooking, and the rice is kept warm. did it.
[0005]
However, in this case, considering the long-time heat retention for 18 hours or 24 hours after the end of cooking, it is insufficient to prevent off-flavors and yellowing due to the growth of thermophilic Bacillus bacteria. There has also been proposed a heat retaining method for operating the heater of the rice cooker approximately every 5 hours after the start of the heat retaining. According to this, since the thermophilic Bacillus bacteria in the heated cooked rice is reheated when it begins to grow, the growth of the thermophilic Bacillus bacteria is suppressed during the prolonged incubation of the cooked rice to prevent off-flavors and yellowing from the cooked rice. I was able to.
[0006]
The long-time heat retention function that reheats cooked rice several times as described above is generally set by turning on the heat retention switch for a long time before starting rice cooking. A timer is activated at the same time as the heat retention operation in which the long-time heat retention function is activated, and the heater is activated after a predetermined time has elapsed from the time when the heat retention was started.
[0007]
However, in the case of having a heat retaining function of reheating once after a predetermined time from the start of heat retention after the completion of rice cooking, the heat retention switch may be turned on for a long time after the reheating has already been performed. For example, when a lot of cooked rice remains after eating, or when the rice is cooked but not eaten for a while, after the heat insulation has been started, it has already been reheated once by the heater. The long-time heat retention switch may be turned on. In such a case, since the long-time heat insulation function starts working when the long-time heat insulation switch is turned on, the timer is driven from the time when the long-time heat insulation switch is turned on and the heater is operated after a predetermined time has elapsed. Will be allowed to. For this reason, the second reheating operation is performed at a time that is considerably longer than the originally scheduled second reheating time after the first reheating, so that it is already preferable in the cooked rice. The growth of thermophilic Bacillus bacteria progresses, and in the worst case, the bacteria may have grown to give off a bad odor at the 18th and 24th hour.
[0008]
The present invention includes a “rice cooker that heats the rice cooker during rice cooking and a heat insulation heater that heats the rice cooker during heat retention”. Even if the long-time heat retention function is set after the cooking is performed, the problem is to keep the heat so that delicious rice can be eaten for a long time.
[0009]
[Means for Solving the Problems]
The technical measures taken to solve the above problems are as follows.
[0010]
As a method of keeping the cooked rice, “After cooking the cooked rice, while keeping the cooked rice at about 70 ° C. with the warming heater, the cooked rice heater is temporarily turned on at a reheating time after a predetermined time from the start of the warming. In the method for keeping rice cooked, the rice is reheated within a temperature range of 80 ° C. to 110 ° C.
If the time for which the long-time heat-retaining switch for performing the reheating is performed several times is before about 4 hours have elapsed since the reheating, the second and subsequent reheatings are performed for about 4 hours from the first reheating. Every time, after about 4 hours from the reheating, the second reheating is immediately performed, and the third and subsequent reheating is performed about every 4 hours from the second reheating. Features. ]
The technical means operates as follows.
[0011]
If the time for which the heat retention switch for a long time to turn on the reheating is turned on is about 4 hours after the first reheating, the second and subsequent reheating will be performed after the first reheating. Perform every 4 hours. As a result, the second and subsequent reheating is performed about every 4 hours after the first reheating without being performed about 4 hours after the long-time heat insulation switch is turned on. Since the spore-type thermophilic Bacillus surviving even after reheating is reheated according to the time of germination and growth, the viable count of thermophilic Bacillus in the vegetative type is effective over 24 hours. (See FIG. 4).
[0012]
Also, if the time for which the long-time heat retention switch is turned on is about 4 hours after the first reheating, the second reheating is immediately performed, and the third and subsequent reheating is performed for the second time. About every 4 hours after reheating. As a result, the second reheating is performed at a time close to the time zone without much delay from the time zone in which the spore-type thermophilic Bacillus bacteria that survive even after the first reheating germinate and grow one after another. It can be reheated.
[0013]
In this way, after the first reheating, the spore-type thermophilic Bacillus that survives even after one reheating is germinated one after another regardless of the time for which the heat retention switch is turned on for a long time. Since it is reheated at the time of growth or at a time close to this time zone, the effect of inhibiting the growth of the thermophilic Bacillus is great.
[0014]
Moreover, the relationship between the heating temperature at the time of the reheating of the said rice cooking heater and heating time shall be 1 second-5 minutes for the cooked rice in a rice cooking pot within the temperature range of 80 to 110 degreeC. This is because the thermophilic Bacillus bacteria in the spore type maintain the number even when the cooking temperature is 100 ° C. and heating for about 20 minutes, but the vegetative thermophilic Bacillus bacteria causing the off-flavor and yellowing are Since the number decreases when the heating temperature is 80 ° C. or higher, it is possible to reliably suppress the growth of thermophilic Bacillus bacteria that cause off-flavors and yellowing in the cooked rice. Moreover, since the upper limit of the heating temperature of cooked rice is 110 ° C. or less, drying of cooked rice can be suppressed, and especially the cooked rice at the bottom of the rice cooker does not dry out and become hard. Furthermore, the heating time of 1 second to 5 minutes can reduce the vegetative thermophilic Bacillus even when heated for 1 second, while proceeding with the drying of cooked rice if heating is performed within 5 minutes. Nor. Then, when the operation of the rice cooker is stopped, the temperature is lowered to about 70 ° C. within approximately one and a half hours (see FIG. 3). From this, heating necessary for damage to thermophilic Bacillus bacteria can be performed without applying excessive heat to dry rice.
[0015]
And, as a rice cooker, “the above-mentioned heat-retaining heater, a heat-retaining heater control unit that controls the operation so that the cooked rice is heated to about 70 ° C. after cooking,
Operation control so that the rice cooker is temporarily operated at a reheating time after a predetermined time from the start of the heat retention by the heat retaining heater, and the cooked rice is reheated within a temperature range of 80 ° C to 110 ° C. A rice cooker controller to perform,
A long-time heat retention switch for causing the reheating operation by the rice cooker to be performed several times,
A storage unit for storing the first reheating time;
If the time for which the long-time heat-retaining switch is turned on is before about 4 hours from the time when the reheating is started from the rice cooking end time in the storage unit, the second and subsequent reheating is performed from the first reheating. About every 4 hours, and after about 4 hours since the reheating, the second reheating is immediately performed, and the third and subsequent reheatings are performed every about 4 hours from the second reheating. In the case of “equipped with a heat retention control unit to be performed”, the same operation as the heat retention method is achieved by controlling the operation of the rice cooking heater by the heat retention control unit when the cooked rice is warmed.
[0016]
In the above technical means, in the case of “the reheating time is 6 to 8 hours after the start of heat retention”, the first reheating causes the yellowing and the off-flavor when the cooked rice is warmed. The thermophilic Bacillus germinates and grows at about 70 ° C. suitable for heat preservation of cooked rice, and after the heat insulation starts, the thermophilic Bacillus fungus grows most actively for 6 to 8 hours (see FIG. 4). Since it matches with the time zone, the growth suppression effect on the thermophilic Bacillus in the first reheating is large.
[0017]
In the rice cooker, even if “the reheating time is 6 to 8 hours after the start of heat retention”, the same effect as that of the heat retention method is exhibited.
[0018]
【The invention's effect】
According to the present invention, the spore type that has survived even after one reheating even when the heat retaining function is set for a long time after the reheating by the heater has already been performed once after the heat retaining is started. Since the time when the thermophilic Bacillus germinates and grows one after another, or reheats at a time close to this time zone, the growth of the thermophilic Bacillus in the cooked rice can be effectively suppressed, and as a result, After cooking, you can eat delicious rice for a long time.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
FIG. 1 is a cross-sectional view showing a configuration of a gas rice cooker according to an embodiment of the present invention. As shown in FIG. 1, a gas rice cooker 1 according to an embodiment can be opened and closed to a rice cooker 2 that contains rice or the like and cooks it, an outer container 3 that contains the rice cooker 2, and the outer container 3. , A gas heater 5 as a rice cooker provided below the bottom of the rice cooker 2, an electric heater 7 provided so as to surround the gas burner 6 constituting the gas heater 5, And a temperature sensor 8 provided to come into contact with the bottom surface of the rice cooker 2. Moreover, the ignition device 9 is arrange | positioned in the vicinity of the said gas burner 6, and the reheating operation | movement by the said gas heater 5 is performed several times after the rice cooking switch 16 which performs rice cooking in the upper part, and rice cooking is completed. A long-time heat retention switch 17 is arranged. Moreover, this gas rice cooker 1 is provided with the timer for measuring heat retention time (not shown).
[0021]
The operations of the gas heater 5 and the electric heater 7 are controlled by a control device 10 including a microcomputer. The control device 10 includes a rice cooking control unit 11, a heat retaining heater control unit 12, a gas heater control unit 13, a memory 14 that stores the first reheating time after the completion of rice cooking, and a heat retaining control unit 15. Is provided.
[0022]
The rice cooking control unit 11 controls the operation of the gas heater 5 in accordance with the set rice cooking pattern, and performs the rice cooking operation while controlling the ignition timing, the fire extinguishing timing, the heating power, and the like.
[0023]
After the rice cooking operation is finished by the heat retaining heater control unit 12, the electric heater 7 is controlled to keep the inside of the rice cooker 2 at a constant temperature. In this embodiment, the heat retention temperature is set to about 70 ° C.
[0024]
The gas heater control unit 13 causes the gas heater 5 to temporarily operate at a reheating time after a predetermined time from the start of heat insulation by the electric heater 7, and the cooked rice is heated to a temperature of 80 ° C. to 110 ° C. Control the operation to reheat within the range. In the present embodiment, the predetermined time is set to 7 hours.
[0025]
If the time for which the long-time heat-retaining switch is turned on by the heat-retaining control unit 15 is before about 4 hours have elapsed from the time when rice cooking is completed in the memory 14 and the re-heating is performed, the second and subsequent re-heating is performed. The reheating is performed about every 4 hours after the first reheating, and if about 4 hours have elapsed after the reheating, the second reheating is immediately performed, and the reheating after the third is performed for the second time. Allow approximately 4 hours after reheating.
[0026]
In the present embodiment, the electric heater 7 is used as a heat-retaining heater, but other heat sources such as a halogen lamp may be employed.
[0027]
Next, the heat insulation operation | movement of the gas rice cooker 1 by this Embodiment is demonstrated.
[0028]
FIG. 2 is a flowchart showing a flow of control after the start of the heat insulation operation. FIG. 3 shows the temperature change when reheating the rice cooker 2 for 3 minutes, the solid line shows the temperature change at the bottom of the cooked rice in the rice cooker 2, and the chain line shows the temperature change at the top of the cooked rice in the rice cooker 2. ing. FIG. 4 shows the change in the viable cell count (cells / g) of thermophilic Bacillus by reheating.
[0029]
In this Embodiment, when performing rice cooking operation | movement, the amount of rice is detected from the heating time etc. in which the inside of the rice cooking pot 2 reaches predetermined | prescribed temperature, and this is utilized as information at the time of heat retention operation | movement. This rice amount detection is performed by the rice cooking control unit 11 of the control device 10. First, after finishing the rice cooking operation, the heat insulation operation is started. In this warming, the warming heater controller 12 energizes the electric heater 7 intermittently while detecting the temperature of the bottom of the rice cooker 2 by the temperature sensor 8 to keep the inside of the rice cooker 2 at about 70 ° C. The insulation by the electric heater 7 works effectively even during operation of the gas heater 5 described below.
[0030]
As shown in FIG. 2, when the warming operation is started, the warming control unit 15 monitors whether or not 7 hours have elapsed since the start of warming (S101). When 7 hours have elapsed, the time at this time is stored as the first reheating time in the memory 14 in the control device 10 (S102), and then the gas heater 5 is operated by the heat retention control unit 15. The temperature of the rice cooker 2 is rapidly increased. At this time, in this Embodiment, first, according to the rice quantity which the rice cooking control part 11 detected by rice cooking operation | movement, the gas heater control part 13 determines heating time (S103, S104). Thereafter, the gas heater 5 is operated (S105, S106, S107). When the amount of rice is “small”, it is heated for 1 minute (S108), and when the amount of rice is “medium”, it is heated for 2 minutes (S109). ), When the amount of rice is “large”, it is controlled to heat for 3 minutes (S110). In the present embodiment, the case where the amount of rice is “large” will be described. Then, the cooked rice temperature is about 85 ° C. at the top of the cooked rice and about 100 ° C. at the bottom of the cooked rice (near the bottom of the cooker 2) (see the seventh hour in FIG. 3), and the temperature of the cooked rice in the cooker 2 is 80 ° C. It will be in the range of ~ 110 ° C. The viable count of thermophilic Bacillus in the cooked rice at this time is about 10 immediately before reheating. ^Four The number per piece / g is reduced to 100 pieces / g or less by reheating (see the seventh hour in FIG. 4).
[0031]
In addition, even when the amount of rice is “small” and “medium”, the temperature of the cooked rice is configured to be within a range of 80 ° C. to 110 ° C. depending on each heating time. As described above, the temperature of the cooked rice is kept within the range of 80 ° C. to 110 ° C. When the temperature exceeds 110 ° C., the lower portion of the cooked rice in the rice cooker 2 is crisply dried, whereas it is less than 80 ° C. If so, it is not possible to reduce vegetative thermophilic Bacillus bacteria that are mixed in cooked rice and cause odor and yellowing. That is, in order to reduce the number of thermophilic Bacillus bacteria and prolong the growth stop time, it is desirable to increase the heating temperature of the cooked rice and to set a longer time for maintaining the heating temperature. However, if the heating temperature of the cooked rice is too high or the heating time is too long, the cooked rice is dried earlier, and on the contrary, the taste is lowered. On the other hand, in order to prevent off-flavor and yellowing from cooked rice, the viable count of thermophilic Bacillus bacteria in the nutritional form is set to at least 10 ⁶ It is sufficient to reduce the number to pieces / g or less. Therefore, if the temperature of the cooked rice is raised to 80 ° C. to reduce the number of viable bacteria of the thermophilic Bacillus, the off-flavor and yellowing from the cooked rice can be stopped. In addition, it can be expected that the number of viable bacteria of thermophilic Bacillus is reduced in the heating time of 1 second to 5 minutes. In particular, according to the gas heater 5 as in the present embodiment, as a characteristic of gas heating with respect to electric heating, the temperature can be raised to a set temperature in a short time with a gas fire. The temperature is raised to about 100 ° C. with the cooked rice at the bottom of the rice cooker, which is easy to add, and raised to about 85 ° C. at the top of the cooked rice, which is not easily heated (see FIG. 3). Thereby, the proliferation of the thermophilic Bacillus bacteria which brings out a strange odor and yellowing from cooked rice can be suppressed. From this, heating necessary for damage to thermophilic Bacillus bacteria can be performed without applying excessive heat to dry rice.
[0032]
When the reheating by the gas heater 5 elapses for a predetermined time (in this example, 3 minutes) (S110), the gas burner 6 is extinguished and the operation of the gas heater 5 is terminated (S111). Return to normal warming operation. Then, the cooked rice in the rice cooker 2 is kept at about 70 ° C. at the time when 8 hours and a half have passed after the reheating by the gas heater 5 has been completed.
[0033]
Next, the second and subsequent reheating operations will be described.
[0034]
After the first reheating is performed, when the long-time heat retention switch 17 for performing the reheating several times is turned on (S112), 4 is calculated from the first reheating time stored in the memory 14. It is determined whether or not time has elapsed (S113). If 4 hours have not yet elapsed, the monitoring operation in step S113 is repeated, and the standby state continues until 4 hours have elapsed. Then, if 4 hours have passed since the first reheating while continuing this standby state, or if 4 hours have already passed when the heat retention switch is turned on for a long time in step S112, the timer is set. After driving (S114), the gas heater 5 is operated by the heat retention control unit 15 to rapidly increase the temperature of the rice cooker 2 (S115). As the heating time at this time, it is operated for 3 minutes as in the first reheating (S116). In this example, it is assumed that the first reheating is performed 7 hours after the start of heat retention, and the long-time heat retention switch 17 is turned on 4 hours after the first reheating. To do. Therefore, the second reheating is performed 11 hours after the start of heat retention. Then, in FIG. 3, when the cooked rice temperature at the 11th hour is seen, the cooked rice in the rice cooker 2 is within the temperature range of 80 ° C. to 110 ° C. as in the first reheating at 7 hours. The temperature is raised. At this time, when the thermophilic Bacillus in the cooked rice is seen around the 11th hour in FIG. 4, it gradually grows after the end of the first reheating, and immediately before the second reheating, ^Three Although it increased to the number per piece / g, it turns out that it decreased to 10 piece / g or less again by reheating. When this second reheating elapses for a predetermined time (3 minutes in this example) (S116), the operation of the gas heater 5 is terminated (S117), and the normal heat retaining operation is resumed.
[0035]
Next, it is determined whether or not the reheating has been executed three times since the start of heat retention (S118). That is, in this Embodiment, after the completion of rice cooking, it is set to perform reheating three times by the gas heater 5 after the start of heat retention. At this time, since reheating is performed only twice, in this case, the process is returned to before step S113 (S118). Then, as the third reheating, the time measured by the timer is monitored, and after 4 hours have elapsed from the start of the second reheating (S113), the timer is reset and turned on ( S114), the gas heater 5 is operated again for 3 minutes, and the temperature of the rice cooker 2 is rapidly increased (S115, S116). The third reheating is performed 11 hours after the second reheating is started, so that the third reheating is the 15th hour from the start of the heating. Then, in FIG. 3, as in the case of the first reheating after 7 hours and the second reheating after 11 hours after 4 hours, the cooked rice in the rice cooker 2 is 80 ° C. to 110 ° C. The temperature is raised within a temperature range of ° C. As a result, thermophilic Bacillus bacteria in the cooked rice gradually grew after the second reheating, when the vicinity of the 15th hour in FIG. 4 was observed, and 10 immediately before the third reheating. ² Although it increased to the number per piece / g, it turns out that it decreased to 10 piece / g or less by reheating. Then, when this third reheating elapses for a predetermined time (3 minutes in this example) (S116), the operation of the gas heater 5 is terminated (S117).
[0036]
Thereafter, after the third reheating is executed (S118), the first reheating time is cleared from the memory 14 (S119), and the normal heat retaining operation by the electric heater 7 is resumed.
[0037]
Thus, when the thing of the 24th hour rice cooked 24 hours after completion | finish of rice cooking was evaluated, the problem which became hard or stuck to the bottom of the rice cooking pot 2 was not seen. Moreover, none of the smell, color or taste of the cooked rice was particularly worrisome. In this respect, the viable count of thermophilic Bacillus is about 10 ⁷ In the case of this example, the quality of the cooked rice is supported by the fact that it was about 10 pieces / g in the case of 24 hours in FIG. In addition, there is an interval of 4 hours or more, which is the second and third time intervals, from the third heating time point of the last reheating to the 24th hour. Since the number of thermophilic Bacillus bacteria is effectively reduced, it can be seen that the thermophilic Bacillus bacteria have not grown to a number that gives off a bad odor even at the 24th hour.
[0038]
As described above, in the present embodiment, even if the heat retention function is set for a long time after the reheating by the heater has already been performed once after the heat retention is started, the thermophilic Bacillus bacteria in the cooked rice Proliferation can be effectively suppressed, and as a result, delicious cooked rice can be eaten for 24 hours after the end of cooking. That is, in the cooked rice, about 10% of the number of viable bacteria is present in the form of spores as the thermophilic Bacillus bacteria grow, and after one reheating, these spores are germinated one after another. Since the time zone for becoming a vegetative type is about 4 hours later, the rapid growth of thermophilic Bacillus is suppressed by setting the time interval between the second and third reheatings every 4 hours. be able to. In the present embodiment, the case where the long-time heat retention switch 17 is turned on when four hours have not elapsed since the first reheating is shown is shown, but even when four hours have already elapsed, Since the gas heater 5 is immediately reheated, the reheating can be reheated at a time close to the time zone without much delay from the time zone in which the thermophilic Bacillus in the cooked rice is most proliferated. it can.
[0039]
In addition, the reheating by the gas heater 5 during the heat retention may be three times in the heat retention for 24 hours (7 hours, 11 hours, and 15 hours later), and the conventional method in which reheating is performed 4 times every 5 hours. Compared with Japanese Patent Laid-Open No. 9-276134, drying of cooked rice can be prevented and energy saving for one reheating can be achieved.
[0040]
In the embodiment described above, the reheating time by the gas heater 5 is 1 minute, 2 minutes, or 3 minutes, but may be appropriately determined between 1 second and 5 minutes. In addition, as the first reheating, the first reheating time is 7 hours after the start of the heat retention, but may be appropriately determined between 6 and 8 hours later.
[0041]
Moreover, although the reheating time is prescribed | regulated as mentioned above, since the cooked rice of the bottom of the rice cooking pot 2 may be burnt according to the amount of rice, the set temperature (rice cooking fire extinguishing temperature or rice cooking fire extinguishing temperature) is reached within the reheating time. When the temperature reaches a lower temperature (for example, 110 ° C.), the heating operation may be terminated by giving priority to the set temperature.
[0042]
In addition, the amount of rice is controlled to be divided into three stages of large, medium and small, and the heating time of the gas heater 5 is selected. However, depending on the capacity of the rice cooker, the amount of rice, the capacity of the gas heater, etc. Alternatively, it may be determined appropriately, for example, divided into two stages of large and small rice.
[0043]
Moreover, it controls so that operation | movement of the gas heater 5 will be complete | finished when the rice temperature of the lower part in the rice cooker 2 reaches 110 degreeC, without selecting the heating time of the gas heater 5 with the above rice quantity. You may do it. It is estimated that if the lower cooked rice temperature reaches 110 ° C, the upper cooked rice temperature also reaches 80 ° C or higher, and the cooked rice temperature in the rice cooker 2 is generally in the range of 80 ° C to 110 ° C. Because it fits inside.
[0044]
Moreover, although the gas heater 5 is used for the reheating, an electric heater may be used for the reheating, and in this case, the electric heater 7 that is normally kept warm may be used. A dedicated electric heater may be provided separately from this. Furthermore, it may be applied to an electric rice cooker instead of a gas rice cooker as in this example. In the case of this electric rice cooker, an electric heater that performs rice cooking or an electric heater that performs normal heat retention is also used for the reheating. Alternatively, an electric heater dedicated to reheating may be provided separately. However, electric heating is sufficient to suppress the growth of thermophilic Bacillus bacteria in cooked rice, although it is slightly inferior in terms of the rate of temperature rise and heat around the cooked rice compared to gas heating.
[0045]
On the other hand, the second and third reheating times are set to be the same as the first reheating times, but the maximum temperature at the bottom of the rice cooker 2 at the first reheating is set in the control device 10 or the like. The second and third reheatings may be controlled so as to end when the temporarily stored maximum temperature is reached.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a gas rice cooker according to an embodiment.
FIG. 2 is a flowchart showing a control flow after the start of a heat retaining operation in the embodiment.
FIG. 3 shows the temperature change when reheating the rice cooker 2 in the embodiment for 3 minutes, the solid line shows the temperature change at the bottom of the cooked rice in the rice cooker 2, and the chain line shows the temperature change at the top of the cooked rice in the rice cooker 2. Respectively.
FIG. 4 shows a change in the viable cell count (cells / g) of thermophilic Bacillus by reheating in the embodiment.
[Explanation of symbols]
1 Rice cooker
2 Rice cooker
3 Outer container
4 lid
5 Gas heater
6 Gas burner
7 Electric heater
8 Temperature sensor
9 Ignition device
10 Control device
11 Cooking rice control part
12 Insulation heater controller
13 Gas heater controller
14 memory
15 Thermal insulation control unit
16 Rice cooker switch
17 Long-time insulation switch

Claims

A rice cooker that heats the rice cooker during rice cooking, and a heat insulation heater that heats the rice cooker during heat insulation,
After the cooking of the cooked rice, the cooked rice is heated to about 70 ° C. by the warming heater, while the cooked rice heater is temporarily operated at a reheating time after a predetermined time from the start of the warming. In the heat-retaining method for cooked rice that is reheated within a temperature range of 80 ° C to 110 ° C,
If the time for which the long-time heat-retaining switch for performing the reheating is performed several times is before about 4 hours have elapsed since the reheating, the second and subsequent reheatings are performed for about 4 hours from the first reheating. Every time, after about 4 hours from the reheating, the second reheating is immediately performed, and the third and subsequent reheating is performed about every 4 hours from the second reheating. A characteristic method of keeping cooked rice.

In the heat-retaining method of cooked rice according to claim 1,
The reheat time is 6 to 8 hours after the start of the heat retention.

In a rice cooker comprising a rice cooker that heats the rice cooker during rice cooking, and a heat insulation heater that heats the rice cooker during heat insulation,
A warming heater controller that controls the warming heater so that the cooked rice is warmed to about 70 ° C. after cooking,
Operation control so that the rice cooker is temporarily operated at a reheating time after a predetermined time from the start of the heat retention by the heat retaining heater, and the cooked rice is reheated within a temperature range of 80 ° C to 110 ° C. A rice cooker controller to perform,
A long-time heat retention switch for causing the reheating operation by the rice cooker to be performed several times,
A storage unit for storing the first reheating time;
If the time for which the long-time heat-retaining switch is turned on is before about 4 hours from the time when the reheating is started from the rice cooking end time in the storage unit, the second and subsequent reheating is performed from the first reheating. About every 4 hours, and after about 4 hours since the reheating, the second reheating is immediately performed, and the third and subsequent reheatings are performed every about 4 hours from the second reheating. A rice cooker characterized by comprising a heat-retaining control unit.

In the rice cooker according to claim 3,
The reheating time is 6 to 8 hours after the start of heat insulation.