Published: Jan 30, 2017

Espresso Recipes: Measuring Yield

After Strength, the 2nd step to every good espresso recipe is yield.

Yield is the amount of espresso in the cup after extraction. It’s measured by weight though—definitely not volume. Before we delve too deeply into yield, I’m going to explain why it’s best to use weight to measure your espresso.

This is probably old news to a fair few of you, but I really want to drive this one home. The time has come. Throw out your measuring cups, 30ml jiggers and shot glasses. Volume is out. Weight is in. Get a scale, and start weighing those espressos!

Using volume to measure espresso is fraught with error and inconsistency. There’s a few reasons why it should be avoided.

 

Shot Glasses Are Small

A small vessel doesn’t leave much margin for error when making a reading. This means that any measurement errors are amplified. A misread of 1mm in a regular shot glass could mean an error of up to 5% of the total volume.

Usually, one should measure a liquid by lining their eye up with the base of the meniscus.

It’s quite difficult to measure the depth of a liquid by eye. It’s even harder with an opaque liquid like espresso. You can’t see the meniscus, which adds another level of inaccuracy.

 

Crema Changes Daily

This is the most pressing reason not to use shot glasses for espresso.

When coffee is fresh, the crema is much thicker. This is because there is still a lot of carbon dioxide in the beans that hasn’t escaped.

As a coffee ages after roasting, that carbon dioxide dissipates and the espresso has much less crema.

Crema is mostly air and its density is far lower than the espresso liquid below, which makes volume measurements close to meaningless.

If you make the same coffee on day 3 and day 14 after roast, the amount of crema it produces will be significantly different. If you used a shot glass to control the size of those two espressos, they would be completely different. The error here can be enormous.

Get Some Proper Scales

Most espresso bars use cheap almost-disposable scales from eBay or wholesalers. They last a few weeks and are reasonably accurate. If water gets in, they’ll probably die or see problems until dried. Initially cheap, but wasteful and potentially expensive if they’re replaced regularly.

Luckily, it seems like manufacturers are finally starting to listen to the baristas of the world. At SCAA this year, acaia launched a water-resistant scale called the Lunar. Initial reports are all positive and following the success of their Pearl scale, I’m comfortable recommending this as the best option without hesitation. Pricey yes, but for form and function in a drip-tray scale, it looks hard to beat.

(Not paid to say that, we swears. I mean, just look at the sucker! And it feels so nice and hefty in the hand… like some iPhone 1 vs iPhone 5 type stuff – AB)

Here’s the announcement and detailed blog post from acaia.

 

How to Weigh Your Yield

If you’ve never made espresso to weight before, here’s a very quick guide:

  • Grind, weigh, distribute and tamp your usual dose into the basket.
  • Tare/zero your cup on a small set of scales.
  • Start the espresso shot and place the cup beneath the spouts.
  • Raise the cup and slide the scales beneath.
  • Make sure the scales are level and reading correctly.
  • Stop the shot when the screen reads a few grams below your yield target weight. This varies from 2-8g due to portafilter retention and scale refresh speed.

Don’t weigh single espressos and multiply by 2. That can be very inaccurate. If you have to split, weigh both cups under both spouts.

Scales Are Best-Practice

The best chefs, bakers, chemists and jewellers all use scales to weigh their stuff. This is because they require both accuracy and precision.

Both accuracy AND precision you ask? What’s the difference? Here’s a great video explaining:

Here’s the team at ChefSteps comparing scales to measuring cups and spoons:

Head to acaia to check out the Lunar—they’ll be in stock and shipping mid-July.

Do you have a favourite set of scales? Let me know in the comments. I’m keen to see what everyone is using!

 

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2 Comments

  1. andrew.taylor

    Thanks for this, folks! Been wondering since we’ve been weighing every pull and I’ve been wondering if I’m introducing too much of a bottleneck. I’d imagine gauging by line could work IF you’ve dialed in for the same bag and marked where the line should be for that bag, though I’d imagine there’s more gas-off at the top of the bag than at the bottom.

    • BHLearn

      Well done you, for paying so much care and attention to your shots. For sure it’s a little time consuming using scales for every pull. If your machine doesn’t have any volumetric (or gravimetric) capabilities built in, then our policy is that it’s essential to weigh every pull. But if you do have some automation available, don’t rule out the possibility that these may be acceptably precise. Many modern machines are surprisingly good in this area, usually with less than a 5% margin of error. Moreover, a gram of water at the end of a shot has a lot lower TDS than at the start of a shot. That can mean that shots that differ by a gram or two in weight may not be appreciably different in a blind taste test. It’s worth testing the machine out over several cycles, and doing some blind taste tests to determine what level of precision and accuracy you really require in your business. If your volumetrics turn out to be ‘inaccurate’, but are still ‘precise’, you can easily work around that by creating a slight offset when you program them. That might help to avoid any bottle neck. But if there’s no volumetrics, or if they are neither precise nor accurate, then you must boldly weigh those shots 😀

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