REACTION ENGINEERING UNDERSTANDING OF BARLEY AND MALT ROASTING

0 REPORT ON ADVERSE DRUG REACTION 1 REPORTER (DOCTOR
1 COMPARE THIS REACTION TO THE ONE USED FOR
195 THE MAGIC WAND (REACTION OF POTASSIUM CHLORATE AND

198 REDOXREACTION WITH MANGANESE DESCRIPTION A MANGANESE (II) SOLUTION
1991 OCTOBER 11TH CONSULTANTS MEETING OF NUCLEAR REACTION DATA
223 THE REACTION IN A BREATHALYZER TEST SOURCE ADAPTED

Reaction engineering understanding of barley and malt roasting

Reaction engineering understanding of barley and malt roasting - AFM88


Sponsor: DEFRA


Partners: Brewing Research International, Pure Malt Products, Simpsons Malt, Omron Electronics, University of Birmingham, University of Leeds


Total Project Cost: £289,332


Start date/End date: 01/10/1999 – 30/09/2002


Project Co-ordinator: Miss Catharine O'Shaughnessy, Brewing Research International, Lyttel Hall, Nutfield, Surrey RH1 4HY

Tel: 01737 822 272 Direct Tel: 01737 824 267 Fax: 01737 822 747 Email: [email protected]


Abstract

Roasted products of raw barley, green malt and white (kilned) malt provide beverage and food manufacturers with a means of modifying the flavour and colour of their final products. Currently, control of the process is totally reliant on hand evaluation of colour during processing by artisan staff. As experienced operators retire and specifications become stricter, a better understanding of the process, leading to better control, is required. This project addressed this problem, the main aim being to gain a basic understanding of the physical processes and the patterns of colour and flavour development, together with their interactions, which take place during the roasting of cereals.


Results

Colour development proceeds by a variety of mechanisms. The simplest are pyrolysis and caramelisation. However, the most important one (for colour and flavour development) is the Maillard reaction. This is the reaction of reducing sugars (such as glucose and maltose) with amino acids and proteins. The browning of crystal malt has been successfully modelled using data on the browning of stewed endosperm. Temperature and roasting time were the critical conditions having an effect of the rate of browning. The model is applicable to crystal malts upto a colour of 250EBC. Above this colour a different reaction mechanism appears to take place.

A spouted bed roaster has been designed and built at the University of Birmingham and used to produce circa 500 grams of speciality malts. These include both dry roasted products (eg roast barley and roast malt) and wet roasted product (eg crystal malt). The products produced are representative of commercial product. In addition, pilot scale and commercial trials have been carried out to gain a better understanding of the roast process as performed by industry. To complete the pilot scale work, PEPT has been used to model the particle mixing in a replica of the pilot scale rotating drum.

A heat and mass transfer model that successfully predicts the temperature and moisture time profiles of the grains as they are roasted within the spouted bed for both dry and wet roasted products has been developed. The kinetic model for the colour development of crystal malt (produced at the University of Leeds) has been used to show good agreement between measured and predicted colour for crystal malt produced on the spouted bed. A colour model for roast barley has also been developed and fitted to measured data. Some work has been carried out to scale-up the model from the spouted bed (500 grams) to the industrial drums (2-3 tonnes), and to account for differences in colour development at the same mean grain temperature that is seen between the laboratory and industrial scales.

Flavour development during roasting has been successfully measured analytically using chemical marker compounds representing the major groups of flavour active compounds and by flavour profiling using an expert taste panel. The marker compounds chosen contribute typical flavours found in roasted products and the majority of these compounds were not detected until after an hour of roasting. Sensory data agreed well with GC data in that papery, green and malty flavour notes were replaced with burnt, bitter, smoky notes an hour into roasting. The results suggest that flavour development precede colour formation. This is not surprising, as flavour compounds are very potent colour formers. In all cases, greatest colour development occurred in the last 10-15 minutes of roasting. The sensory data showed that high colour end products were less flavour intense (bitter, burnt, harsh) than samples taken earlier in the time course. This was corroborated by the GC data, which showed a reduction in the concentration of some heterocyclics (particularly pyrazines), towards the end of roasting. Certain thiazoles and pyrazines were not detected in amber or crystal malt and their formation appears moisture and/or temperature dependent. It may be feasible therefore to promote or inhibit the formation of certain flavours just by manipulation of the air temperature entering the roaster. This in turn will affect moisture and product temperatures, which in turn will affect the formation of certain flavour compounds.

The software for the Fuzzy Logic Flavour Model has been developed. The model is 2-rule based: the first linking process conditions to ‘key’ flavours and the second linking the ‘key’ flavours to the other flavour labels. Correlation analysis established that five key flavours could be used as predictors for 11 of the others. A process model has been developed that relates the key flavours to process conditions and is capable of producing good qualitative predictions of the flavour profile achieved when roasting crystal malt. The process model is very simplistic, utilising only maximum grain temperature and germination time as model inputs.


3 BALANCING REDOX REACTIONS – USING OXIDATION NUMBERS A)
ACUTE ALLERGIC REACTIONS AN “ACUTE ALLERGIC REACTION” CAN SOMETIMES
AMMONIA IN UGI REACTIONS FOURCOMPONENT VERSUS SIXCOMPONENT COUPLINGS


Tags: barley and, roast barley, understanding, reaction, roasting, engineering, barley