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, acaialaunched 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)
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 jewelers 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 favorite set of scales? Let me know in the comments. I’m keen to see what everyone is using!
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