Gene Cafe Difference Between Earlier And Later Models

Gene Cafe Secrets and tips for that perfect roast

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I thought I had better add this article for people to read and allow them to put the Gene Cafe vs Hottop roast offs we did into perspective

The Gene Cafes referred to in the tests vs. a Hottop were manufactured Mar 07 and later (shown by a sticker on the back). I understand that earlier Genes sold may have had different revisions of firmware and some were sold with the incorrect heating elements for the countries concerned. Both these things would actually make the earlier Genes roast differently to the later models.

One of our forum thread where the problem was discussed

1. We think the earlier firmware did seem to cause a phenomenon that meant the the heating element would start to cycle on and off before the preset temperature is reached. This actually means less heat energy is applied to the roast and the roasts take much longer. Once you start looking for this "cycling" of the element, it's quite obvious.

2. If a 230V element is used in the UK, which remember was 240V and under EU voltage harmonisation the government only changed the % they were allowed to be above and below 240V. This means that our mains voltage can be anything from around 230V up to 247V. So it might seem that a 230V element would roast faster, but again we believe that this just trips the overheat sensor at the inlet end of the Gene much earlier and actually roasts even slower (I know counter intuitive). A 230V element in the UK is also likely to have a short life.

Even worse people have been told to reduce the batch size in cold weather, in the mistaken belief the Gene will roast faster but it does not (the physics of the Gene also indicate that it would not roast faster). Unfortunately this is counter intuitive and when people put smaller batches in, the Gene gets up to temperature faster, so they think that it's going to roast better? All that is happening is that the heat is going straight through the chamber and warming up the temp sensor at the far end of the machine….if you doubt this, turn your gene on with no beans and watch how fast the temp rises.

So why doesn't it roast faster?

Well with less beans to trap the heat, less heat energy stays in the roaster, think of the beans like a heat trap. Let's do a quick armchair experiment.

We fill a Gene with 300g of beans and turn it on…the heating element supplies 100 units of heat per minute. The bulk of beans traps 70 units of heat per minute……after 12 minutes 700 units of heat are absorbed by the beans. OK so far so good, now we enter 1st crack and the beans expand by 70%, logically they will trap even more heat lets say 80 units……which is why we reduce the temperature after a minute or so of 1st crack. we are NOT reducing the temperature of the beans all we want to do is supply less than 100 units of heat to bring the trapped heat of the beans back down to 70 units or so. In cold weather with a roster loaded to 300g the preset temp may never be reached, so you simply lower it by 4 degrees or so, from the highest temperature it did reach (don't worry the beans are still getting as hot as with a smaller load).

We fill a Gene with 100g of beans and turn it on…the heating element supplies 100 units of heat per minute. The bulk of beans traps 23 units of heat per minute……after 12 minutes 276 units of heat should be absorbed by the beans. obviously in this scenario, though, the roaster will get hot fast, less heat is being absorbed by the beans….BUT, once the roaster is up to temp it will start cycling the heating element on and off, greatly reducing the overall heat input to the roast (the roaster could be up to temp before 1st crack is reached?).

In the above scenarios we are just using the heat more efficiently and in the first scenario, it's possible that the preset temperature may not be reached….so how can this be the case that it will roast faster?

The exit thermocouple is simply measuring the heat leaving the roaster and is not really the bean temp. In the roaster with 300g the thermal gradient across the roasting chambers length is quite steep, in the roaster with 100g it's very shallow.

So why not use 300g routinely?

Well the steep thermal gradient can cause bean charring except in very cold weather (6C or less when 300g of beans can roast quite dark in as little as 15m 30s). If in doubt check out the shared roast logs here and the entries for 2/7/07 where 300g was roasted and you can see how much faster the roasts were. I also think the life of the heating element might be reduced and the Gene seems happiest at 250g, whether the coffee is chaffy or not.

Conclusions & Recommendations

  1. If you have a 230V element in your Gene and you are in the UK, get a 240V one, it will roast better and have a much longer life (you may have had one or more 230V elements fail already)
  2. Know what your countries true voltage is and get the right Gene
  3. Understand the physics of the Gene cafe….you will get much better roasts
  4. If you have a pre March 07 Gene and it roasts slow (I don't mean a minute or so slower), there is not much you can do except contact your vendor and see if they will help you out. (check out our online roasting logs to see how fast it should roast and we often have ambient temp and mains voltage recorded).
  5. You may read the basic Hottop is superior to the Gene…hmm remember when those comparisons were probably done, were they were on earlier versions of the Gene and possibly done by people who didn't understand the physics of the roaster! You might want to be a little more sceptical of their statements.
  6. The Gene is at least as good as the basic Hottop (in my personal opinion, its far better), but you do have to use it properly
  7. In hot weather you have to use lower preset temps to avoid charring (because the temp gradient in the roaster gets very steep) and definitely need to reduce temp after a minute or so of 1st crack, normally by 4 or 5C. I find that in cold weather 6C you might use a preset of 240 and in hot weather 23C you might be reducing your preset temp to 234 (rough rule of thumb for every 2.5C change in external temp = changing the preset by about 1C
  8. If in cold weather your roasts are too slow move from 250g batch to 260 or 270g….I haven’t had this problem with post March 07 Genes in temps as low as 6C
  9. Weigh your beans, forget using the measuring scoop that comes with the roaster

More hints and tips to come

For a full update on roast times and types of coffee check out our online-roastlog-application