Posted Sun Dec 23, 2012, 6:55pm Subject: Hacking an AutoDrip - helping an old brewer make better coffee.
Here's the best method I found to hack a brewer to produce near "gold cup" standard.
Gold cup is essentially producing a target strength of 1.25% coffee with a brew ratio around 17.4 Water:Coffee.
There's several variables that these machines have buried into an automated process, and lots of opinions of why they fall short or produce inferior coffee.
I pulled out an ancient Hamilton Beach/Procter-Silex 1000W brewer and decided to try it out. Haven't used the thing in prolly 10 years or so.
I tried to fill the basket with 85g of coffee (for about 1500g of brew water). Not good, the basket was pretty full. Then I started the brew cycle, and knew it was bound for failure when I was going past 6 minutes. After almost 8 minutes the brewer started pushing steam (the stuff in the reservoir was gone), and the basket temp quick check was at 206°F.
Most of the time, I've heard that home auto-drip brewers just "don't reach the recommended 205°-195°F temperature", but I figured there was more to it than this. Many times, I've tasted clearly overextracted and bitter coffee from an auto-drip brewer, so if it was an undertemp problem then it would be underextracted, not over.
The strength in the pot that I made was almost 1.45%, implying strongly extracted coffee.
So, after hundreds of experimental cups over the last few years, I've come to learn a few things, and I thought I'd apply it to this brewer before I tossed it.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Sun Dec 23, 2012, 7:10pm Subject: Re: Hacking an AutoDrip - helping an old brewer make better coffee.
A look at the "ideal" drip:
-Decent temperature (>185°F) throughout the percolation session.
-Delivery rate approximately equal to the percolation rate.
-Overall Delivery time (by experience) >3:00, <4:00. That seems like a narrow window, but it does seem to make the best coffee.
Regarding temperature:
Many of the Bunn brewers handle the temperature by a heated reservoir. This is a very clever way to do it, but these brewers start at ~$100, too.
The typical cheap AutoDrip takes water, heats small bits of it to boiling, and the expanding bubbles push the water against a small check valve or check ball up the delivery tube to the top of the brew basket.
The issue is that any water in the tube is essentially room temperature - and this shows in the basket temperature, which starts at ambient, and slowly climbs to boiling. Smaller brewers mean this tube is shorter and therefore the temperature of the delivery water rises more quickly. The 12-cup brewers may take up to a minute to reach delivery water temperature >185°F. This, by itself, isn't strictly a problem - many a decent cup of coffee is made with lower temperature water (if not lacking character).
But, there is some of the explanation. In essence, it's possible to think of this initial slug of cool water as a cool temperature pre-soak. It does help some to reduce bloom.
Eventually, the delivery water in the tube is heated up to temperature, the cycle of boiling bits of water happens quicker, and the delivery rate usually increases toward the end of the brew cycle.
More on that later. We can use this to manipulate parts of the cycle to hit our ideal targets.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Sun Dec 23, 2012, 7:24pm Subject: Re: Hacking an AutoDrip - helping an old brewer make better coffee.
The next part is the percolation rate and the delivery rate.
The percolation rate is determined by the grind fineness, and the depth of the grounds bed. There is an ideal, but it turns out that if the percolation hasn't stalled, there is a fairly large range of grind that works, so long as the ground depth isn't too deep.
The thing we need to know is the delivery rate - and this depends on a one primary factor:
-Temperature of the brew water.
Most of the time, this is around 60-70°F - we take tap water, toss it into the brewer, and click it on. Heat from the brewer bleeds back to the water in the reservoir, and the average temperature is only slightly higher that
So, load up the empty brewer and brew some water-only. Measure the time it takes to brew 1000g or 1500g. Divide by the number of seconds, and the delivery rate is in g/sec.
In my case, it was about 8 minutes for 1600g, or 3 1/3 grams/second.
However, I can reach almost 9 g/sec if I put 170°F water into the reservoir - but if I do, I must use a fairly coarse grind or I overrun the brewer.
This is the starting point - decide what temperature water you will use. Use the delivery rate to set the total delivery time to 4 minutes.
In my case, 800g if I decide to use room temperature water.
To match this with coffee, divide by 17.4 (or 46g of coffee in this example). To start out, use an "auto drip" grind, which is coarser than manual pourover. This is approximately the granularity of something like maxwell house or folgers (except these are ground using roller mills, and will be significantly better control over particle size, shape, and distribution than any of us can achieve with burr grinders).
Set it up, toss in 800g of brew water, check with a timer (in my case, just a bit longer than 4 minutes delivery time), and BINGO. A perfect couple of mugs of coffee out of a $20 brewer. Strength, approximately 1.26%.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Sun Dec 23, 2012, 7:42pm Subject: Re: Hacking an AutoDrip - helping an old brewer make better coffee.
If I want more coffee, I just need to know how hot to make the reservoir water (to jumpstart the delivery and speed up the cycle of boiling, bubble forcing, etc. to deliver hot water).
I found out that I'm around 6-7g/second if I use approximately 150°F reservoir water. Yes, ya need to heat water separately, but this is if you're not willing to drop a Benjamin on a reservoir brewer.
That lets me use about 1500g of brew water delivered in about 4 minutes. Toss in 85g of coffee and 1500g of hot water into the reservoir.
In my case, it took about 4:25 to brew, but the result was still pretty darn good - about 1.3% strength, but this time about four mugs of well-brewed coffee. It looks like fairly fresh Guat Antiqua just touched the top of the brew basket, so I'm at the limit of how much coffee I can put into the basket anyways. Looks like this is the max capability for this little guy.
The key to understanding the autodrip is understanding the delivery rate. Once you understand how to control that, just set the delivery time to 4 minutes and work the grind to work with that delivery rate.
My BCM-4C has a reservoir capacity of around 720g, but the delivery rate with room temp water is only 2g/second. So, I only have a couple of choices:
-4 minutes is about 480g of brew water. I can do around 600g, but the brew time is on the edge of 5 minutes. I've flirted with overextraction doing this. -I can make double strength coffee with 480g brew water, then dilute to two full mugs (four 6oz cups)
Any time I try and brew to full capacity with room temp water in the BCM-4C, I'm pretty much over 22% extraction. The overall brew cycle goes over 6 minutes, which is a bit much even for the maximum grind size of the Bodum Bistro grinder.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
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