2 research outputs found
Fluid-bed type coffee roaster
V procesni verigi proizvodnje in priprave kave predstavlja praženje nepogrešljiv korak, ki lahko poudari njene aromatične karakteristike in trdo delo pridelovalcev, ali pa le te prekrije z zažgano aromo ter kislim priokusom. Kakovost praženja poleg kvalitete surove kave ključno vpliva na tržno ceno končnega produkta. Zelena kavna zrna so med procesom praženja podvržena številnim fizičnim in kemičnim spremembam. Najpogosteje se odražajo kot sprememba barve, podvojitev velikosti zrn ter prepolovitev njihove gostote, pridobitev na sladkosti, povišanju nivoja kislosti in razvoju do 800 novih aromatskih spojin.
Na lastnosti pražene kave močno vplivajo procesni parametri med praženjem, bolj specifično časovno-temperaturne razmere v notranjosti kavnega zrna kot funkcija prenosa toplote. Med praženjem se toplota v kavna zrna prenaša preko mehanizmov kondukcije in konvekcije. Od teh je konvekcija najbolj efektivna in primerna za enakomerno praženje. S pražilniki, ki temelijo na tehnologiji fluidizirane plasti vročega zraka je dosežen skoraj popolnoma konvekcijski prenos toplote, kar omogoča hitro praženje in rezultira v kavi z nizko gostoto in visokim donosom. V primerjavi s temi so tradicionalni pražilniki s horizontalno vrtečim se bobnom, ki delujejo pretežno po principu kondukcijskega prenosa toplote, počasnejši, proizvedejo produkt z večjim deležem defektov zaradi neenakomernega pečenja in zavzamejo več delovnega prostora. Hitro pražena kava vsebuje več topnih trdnih snovi, manjši delež degradiranih klorogeničnih kislin, ohrani več hlapnih snovi in pridobi manj zažganega okusa v primerjavi s kavo, praženo po počasnejši metodi. Hitrejša metoda praženja torej proizvede okusnejši in bolj aromatičen končni produkt
Cilj diplomskega dela je izdelava pražilnika kave, katerega delovanje temelji na tehnologiji fluidizirane plasti vročega zraka. Visok pretok vročega zraka kavna zrna drži suspendirana nad perforiranim dnom pražilne komore, jih vrtljivo meša in konvekcijsko segreva. Pleve, ki se med procesom ločijo od zrn, ter ostale lažje smeti skupaj z izhodnim zrakom napredujejo iz pražilne komore v ciklonski ločevalnik in se zberejo v namenski posodi. Po doseženi želeni stopnji praženosti je potrebno kavna zrna ohladiti v najkrajšem možnem času, da se prepreči nadaljnje neželeno praženje. To je doseženo z vpihavanjem zraka sobne temperature v pražilno komoro. Krmiljenje naprave izvaja mikrokrmilnik Arduino Uno, opremljen z razširitvenim modulom TC4+. Termočlena za merjenje temperature kavnih zrn in izhodnega zraka sta priključena na mikrokrmilnik preko digitalno-analognega pretvornika, lociranega na razširitvenem modulu.
Za gretje zraka skrbi grelni element, povezan preko polprevodniškega releja. Visok pretok zraka zagotavlja zračna črpalka. Krmiljenje naprave poteka na osebnem računalniku s programsko opremo Artisan, ki avtomatizira proces praženja s PID regulacijo, omogoča spremljanje poteka temperature v realnem času z grafom ter podaja relevantne informacije za izboljšanje procesa.In the coffee processing chain, roasting represents an essential step that can either bring out the aromatic characteristics of the coffee or mask them with burnt aromas and acidic undertones. The quality of roasting, along with the quality of the raw coffee, significantly impacts the market price of the final product. Green coffee beans undergo numerous physical and chemical changes during the roasting process. The most significant changes include color transformation, doubling in size, halving in density, gaining sweetness, increasing acidity levels, and the development of up to 800 new aromatic compounds.
The roasted coffee\u27s characteristics are strongly influenced by the process parameters during roasting, specifically the time-temperature conditions inside the coffee bean as a function of heat transfer. Heat is transferred to the coffee beans during roasting through conduction, convection, and radiation mechanisms. Among these, convection is the most effective and suitable for even roasting. Roasters based on fluidized bed technology achieve almost purely convective heat transfer, enabling fast roasting and resulting in coffee with low density and high yield. In comparison, traditional roasters with horizontally rotating drums, which primarily operate through conductive heat transfer, are slower, produce a product with a higher defect percentage due to uneven roasting, and require more workspace. Faster roasting retains more soluble solids, a lower proportion of degraded chlorogenic acids, preserves more volatile substances, and acquires less burnt taste compared to coffee roasted using the slower method. Therefore, the faster roasting method produces a more delicious and aromatic final product.
The goal of this thesis was to create a coffee roaster based on the technology of swirling hot air. A high flow of hot air suspends the coffee beans above a perforated bottom in the roasting chamber, rotating and convectively heating them. Chaff separated from the beans during the process, along with other lighter debris, progresses with the outgoing air into a cyclone separator and collects in a dedicated container. After achieving the desired roasting level, the coffee beans need to be rapidly cooled to prevent further unwanted roasting. This is accomplished by blowing room-temperature air into the roasting chamber. The control of the device is handled by an Arduino Uno microcontroller equipped with the TC4+ expansion shield. A thermocouple for measuring the temperature of the incoming air to the roasting chamber and the temperature of the coffee beans are connected to the microcontroller via a digital-analog converter with cold junction compensation located on the expansion shield. A heating element, connected via a semiconductor relay, is responsible for heating the air, and a high airflow is facilitated by using an air pump. The personal computer and Artisan software automate the roasting process with PID regulation, monitor the real-time temperature graph, and provide useful information to the roaster for process improvement