Chronicles of a Celtic Roaster

Behind the scenes at Carvetii Coffee Roasters

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Cupping Protocols

Today was all about testing our cupping protocols.  We cup coffees to determine a lot about their quality, to help us decide whether to purchase a coffee and to check on the consistency and quality of our roasting.

Every once in a while we go back to basics to check up on our protocols.  

We always use 12g of freshly ground coffee.  We actually grind more than we need to ensure every bowl has exactly 12g.

To this we add 200g of water.  We aim to use water at 95ºC each time.

We brew the coffee for three minutes, after which we break the crust, clean the bowl and wait another five minutes before tasting.

The one variable we need to check is the grind setting.  We do this by measuring the total dissolved solids and extraction in each bowl 1.  If this is in an acceptable range we know we are tasting the coffee and the roasting.

If we feel the extraction is too high or too low we’ll start again having made an adjustment to the grind setting. 

Our aim is to ensure we are tasting a true reflection of the coffee and the roasting, and not a flaw in our brewing technique.

We filter a sample from each bowl, ensuring we take the sample from a consistent point just below the surface. ↩︎

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Blackburn Estate

This morning my coffee of choice has to be Blackburn Estate from Tanzania.  It just happens to be one of my favourite coffees - great fruitiness along the lines of plums, very juicy, lots of sweetness as it cools.  We are now in the middle of UK Coffee Week which apart from celebrating all things good about the industry, aims to raise money for clean water projects in Tanzania and Rwanda.

We’ve put together our Taste of Tanzania to help celebrate UK Coffee Week and to raise a bit of money at the same time.  Order online this week or next and you’ll receive two bags of coffee from Tanzania: Blackburn Estate and Shari AA.  We’ll give £1 from each sale to UK Coffee Week.

You can also enjoy these coffees at our Roastery this coming weekend - we’ll be opening our doors to the public on the 9th and 10th May between 10 am and 4pm.

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Roaster Service

We have a 35 year old Probat GN12 roaster which we bought in 2011, when Carvetii was formed.  We’ve slowly been customising the roasting to allow it to work in a way which suits our growing understanding of coffee roasting.  Last week, as well as a full service, we added some new gas valves and a more accurate bean probe.  

Sometimes things don’t go to plan though!  The front bearings haven’t been removed for a long time and they just didn’t want to budge.  The effort of removing them resulted in the cast iron front of the drum being cracked.  Fortunately it can all be fixed, and with the new bean probe in place we will have a more accurate picture of what is happening within the coffee beans as they roast.

If you’d like to have a closer look at roaster, and develop a better understanding of what we do at Carvetii, we’re opening the doors of our roastery to the public on the 9th and 10th May.  Please feel free to drop in for a coffee.

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New coffee, new sacks

While most of our coffee arrives in hessian sacks made from jute, this is not always the case. The coffee sacks in the photo are our recent delivery of Shari AA coffee from Tanzania, and while they look like jute sacks, they are in fact made from sisal.

Sisal is a coarse fibre, similar to jute, but made from the sinuous leaves of the agave plant. Jute bags are prohibited in Tanzania to protect the local sisal industry. The sisal bags are free of the characteristic odour of jute.

The green coffee beans are also packaged within a Grainpro bag, inside the hessian sack. The Grainpro provides an effective barrier to prolong the freshness of the coffee.

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Seasonal Changes

This week we're roasting the last batch of our Kenyan Karii AA, a coffee we've really enjoyed this season.  While we're sorry to see it end, we are also looking forward to its replacement, which will arrive at the Roastery later this week.

The coffee we have available at any time will depend on the time of year.  The main crop in Kenya is being harvested at the moment, and will be shipped in the coming couple of months.  Depending on the lot we're looking for, we should expect to have this season's Kenyan available to us from early Summer.

Our aim is to buy our coffee as fresh as possible and to use it as quickly as possible.  The longer we keep the coffee on site, the more likely it is to diminish in quality.  This makes buying coffee a bit of a challenge: we need to buy enough to get a return on the investment of time and effort to develop the roast profile.  As a general rule of thumb, we buy enough coffee to last us for around three months.

So if you've been enjoying our Kenyan, I'm sorry to disappoint as it is no longer available.  However, we have an equally delicious coffee from Bolivia arriving later this week and we're eagerly awaiting a couple of different lots of Tanzanian coffee. 

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Visit Original Link

Throughout the coffee roasting process we are monitoring the coffee beans in a variety of ways. While we utilise technology to determine the temperature within the drum and also the rate of change in temperature (read more), we also use our senses to gain an idea of how the roast is progressing. The colour change in the coffee from green through to brown is an obvious visual cue but we also make use auditory cues at various stages in the process.

As a roast progresses, there is a build up of gases within the coffee beans. Around 9 to 10 minutes into the roast, the build of pressure within the beans is too great and these gases are released, with each bean giving off a popping sound as this happens. We call this ‘first crack’ and the attached audio is a recording of one of our roasts last week. We’ll continue to roast the coffee beyond first crack to develop the flavours within the bean.

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In my cup . . .

This time it isn’t coffee but a tisane, or herbal tea infusion, made from dried coffee cherries. Once the coffee bean has been removed from the cherry, the waste material is normally utilised as fertiliser. However, in some instances, this cherry pulp is dried on patios and sold as cascara.

We’ve been aware of cascara for a couple of years now and have sampled it a few times since then. Our first batch was delivered yesterday, an organic Bolivian Cascara, and we were keen to give it a go.

Our first effort, pictured, used 17g of cascara to 200ml of water, brewed over 7 minutes in a coffee press. It had a very sweet intensity with strong cherry flavours. Our second effort was made in a teapot, using twice the quantity of water, brewed for a similar period. The resulting drink was lighter with an apple acidity and more balanced acidity. The drink was wonderfully refreshing and many more brews were made throughout the day.

You’ll can purchase a bag of cascara on our website www.carvetiicoffee.co.uk

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Dialling In

We have a barista training session at the Roastery this morning so before everyone arrives it’s time to dial-in the espresso machines and grinders. This involves pulling espresso shots and making changes to the grinder and espresso machine to ensure the coffee we serve is of the correct quality and matches a specific set of parameters.

There are three key parameters we check: the weight of the ground coffee we are going to use, the time it takes for the shot to extract and the weight of the resulting espresso.

This morning I started with an 18.6g dose of ground coffee, and pulled a 29g espresso over about 28 seconds. The 18g dose is determined by the size of the portafilter baskets I was using, the extraction time of 28 seconds is typical for all espresso we make[1], and the end beverage weight relates to the amount of water we pass through the espresso.

Whenever we set about dialling in the espresso, we always use taste as the deciding factor. We look for a bright acidity, good sweetness as the espresso cools, some body and a lingering aftertaste. We also want to be able to pick up some of the flavours in the coffee.

While this process uses up a bit of coffee, and requires a commitment of time, it is often this attention to detail that separates a good coffee shop from a mediocre one.

We have very soft water at our Roastery (sometimes as low as a TDS of 20ppm) and find that extending the extraction time can counteract the impact of this water, particularly when pulling shorter shots.  ↩

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Coffee Brewing Workshop

Although it is still technically work, we really enjoy sharing our passion for coffee through our Brewing Workshops. It was a full house at the Roastery this morning with four keen participants ready to immerse themselves into the world of hand brewing.

We always start the morning with the obligatory coffee followed by a tour of the Roastery, allowing the participants to get up close to our stock of green coffee beans. Our roaster (Mrs P) always takes centre stage and we’re happy to discuss our own philosophy on coffee roasting.

The rest of the morning is spent trying out various brewing methods, and exploring concepts such as dose, strenght, the impact of the grinder and extraction. We make the sessions as hands-on as possible and there is obviously plenty of coffee to taste. This morning we focussed on coffee cupping, the coffee press (or cafetiere), pourover filter brewing and ended with a session on the Aeropress. Our participants always walk away with a box of goodies to help them practice their new skills at home.

_We run Coffee Brewing Workshops each month at our Roastery. We limit the group size to 4, making it a very informal and fun session. You can find out more details, and book a place at our next workshop on our website. _

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Chaff

Green coffee beans have a silvery, paper thin skin which is called chaff.  When we roast coffee, the beans expand in size and and they shed this chaff.  During the roast, the chaff passes out of the drum and collects in a separate part of the roaster (picture above).

At the end of each roasting day we need to empty this drum and clean the roaster.  The accumulation of chaff can affect the airflow in the roaster (which has a negative effect on the coffee) and also poses a fire risk.  The chaff, being dry and paper thin, is very combustible.

Chaff is nitrogen rich and makes an effective fertiliser if mixed with soil or other mulch material.  Each week we produce at least a bin bag full of chaff and will happily hand it over to any local gardener who can make use of it.  Please contact us if you think you can use chaff in your garden. 

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In my cup . . .

I am a big fan of filter coffee[1] and this morning I took some time out to make a pourover of one of our coffees. I first started using this setup back in 2009, and I suppose it was one of the first brew methods I started using which took me away from the espresso machine. The paper filter in this setup absorbs any oils in the coffee, so the resulting brew has a real crispness to it which I feel lets the coffee flavours come to the fore.

This morning I chose one of our single origin coffees, Inzà. This coffee comes from Colombia and we were introduced to it by our coffee broker, Mercanta. Inzà is a region in Colombia and this microlot has been produced by selecting high scoring coffees from a group of farms in the area. It is a very easy drinking coffee with malty chocolate tones and a creamy mouthfeel.

I used 30g of coffee with 500ml of water at 93ºC. The brew time was a little quick at just over three minutes so the next time I will use a slighlty finer grind.

If you would like to learn more about brewing techniques, we offer Coffee Brewing Workshops at our Roastery. As well as a short tour of our Roastery the three hour session includes an opportunity to try out some different brewing methods under our expert guidance. You can find out more here.

Providing the coffee has been freshly ground and has been freshly served. I am not a fan of the pre-ground filter coffees which sit stewing in glass decanters.  ↩

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Testing extraction

This week we’ve changed the components in our espresso blend which means we’ve needed to develop roast profiles for new coffees. Over the past couple of weeks we’ve been roasting and tasting each of the new components until we’re happy enough to release them into our blend.

As well as making sure the coffee tastes good, we need to ensure the roasts have been sufficiently developed. This will make sure the coffee works when served as an espresso. One way we do this is to pull espresso shots and measure the strength and extraction using a refractometer. The extraction yield, in particular, tells us how much of the coffee we have managed to ‘force’ into the cup. If the extraction yield is high enough then it is likely that the roast has been developed well. If we struggle to achieve a high enough extraction, we will have another look at the roast profile and make some alterations.

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Each and every time we roast coffee, we generate a roast profile. Our roaster is fitted with a digital temperature probe in the drum and this gives us real-time data as the roast progresses. This is plotted as a graph similar to that above.

We charge the drum to a specific temperature before we drop the beans in. We run at around 10kg batch sizes in a Probat 12kg roaster. Throughout the roast we will manually control the temperature in order to follow a roast profile which we will have determined beforehand. For the first half of the roast the beans slowly dry and they remain green in colour. Approximately 6 minutes in and we start to see a colour change. You can see a time lapse video of this in a previous post. We continue to manage the heat applied to the beans right the way through to the end when we stop the roast by dropping the beans into a cooling drum. The above roast is for Inza, a single origin coffee from Colombia.

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Espresso Machine Servicing

Part of our work involves the servicing and repair of espresso machines, grinders and other equipment used to make coffee. This morning I’ve spent a couple of hours with a customer, carrying out an interim service as part of our service contract package.

Much of the time spent working on espresso machines (and grinders for that matter), involves cleaning. Coffee grinds and oils can accumulate throughout the machine and this build up can cause problems in the long term. All the baristas we train are taught how to clean an espresso machine on a day to day basis which, combined with regular servicing, will help ensure a degree of longevity when it comes to the life of the equipment.

As part of our preventative approach to espresso machine servicing, we also test the water quality to ascertain whether there are likely to be any scale or corrosion issues. This information allows us to better inform the customer as to the most appropriate water filtration system for their establishment.

We put a lot of effort into our service contracts because, at the end of the day, a clean, well-maintained espresso machine is going to produce a better coffee.

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One of today's roast as a 27 second time-lapse, showing the change in colour from green bean through to roasted coffee.  Very little colour change happens for the first 11 seconds of the video, which is a period of drying.  After this point, the beans go through a colour change which begins with yellow and works it's way through tan, light brown and onto a darker brown.  The window empties at the end as the beans drop into the cooling tray.

Throughout the roast we use the sampler to check on the development of the beans, and you can see this happening in the video.  Alongside these visual cues we have a temperature probe inside the roasting drum which gives us real-time data on the roast.  This is connected to a computer which allows us to record every roast, which we then compare with how the coffee tastes.  In this way we can determine how  alterations we make to the roast profile affect the coffee. 

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In my cup . . .

I've just taken some time out from processing coffee orders to make myself an espresso.  This one is actually our new seasonal espresso blend which is due to be released next week.  When we change the components in the espresso blend we'll have some formal tasting sessions but I'll also throw a bag into the grinder and play around with the settings.  I often find this informal, unplanned tasting allows me to develop a better idea of the espresso.

There are two components in this blend, Fazenda Pedra Redonda, a pulped natural from Brazil, and Cyiya, a fully washed coffee from Rwanda.  The espresso has a wonderful sweetness and although I think we need to tweak the roast a little, we need to make sure we retain this aspect of it.

I've pulled this espresso as a slightly restricted shot: an 18g dose of coffee to produce a 30g espresso in around 30 seconds.  With the softness of our water I tend to push the extraction time towards the 30 second mark.

I also tend to allow my espresso to cool slightly before I drink it.  As the coffee tends towards room temperature I find it easier to pick up the more subtle flavours, and I know I can appreciate the sweetness more as it cools.

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Coffee Subscription

This week we've been dedicating a bit of time to our coffee subscription customers.  Each month we select a coffee to roast and send out as part of our coffee subscription.  Sometimes the coffee might be part of our range, often it's a pre-release coffee, and sometimes we offer a coffee which is exclusive to our subscription customers.

With each coffee subscription we produce a newsletter giving additional information about the coffee we have sent.  We try to vary the content of these newsletters and include subjects such as coffee sourcing, roasting and brewing.

Our coffee subscription can be purchased as a 6 or 12 month package through our website or a monthly direct debit can be arranged by contacting us directly on [email protected]