VST baskets are not a new piece of equipment by any means. Since their release around 2-3 years ago, many cafes and home espresso enthusiasts have been sold on the idea of a precision-engineered, optimised filter basket and have switched their standard, machine-included baskets for shiny new VST. Read this article by A. Easthope of Five Senses in Australia.
For a seemingly simple set of changes, VST baskets carry plenty of claims which seem to justify investing in them. They address the lack of quality and consistency in the filter-basket manufacturing process and they are designed as a filter basket with precise dimensions, standardised filter holes and a target dose mass for each basket.
In the time that I've been using them I've encountered mixed responses from those who have made the switch. Some users claim greater consistency and the ability to extract their shots in greater volumes without negative effects on flavour; other users have switched back to their old baskets, disappointed with their results and often citing inconsistency, shot-channelling, sloppy coffee-pucks and confusing extraction flow rates as good reasons to stop, cease and desist. Still others really can't see any difference at all, and wonder why they've just spent over $90 replacing their three filter baskets.
So what's the deal here? Are they better, or aren't they? Do we really need them in order to get excellent results?
Well, the quick answer is no. The definition of what constitutes a great espresso is not universally agreed upon. That being said, the above questions and the ‘no' conclusion might also be a little out of context when it comes to VST baskets.
As we have found, the real benefits of using VST baskets comes about when we start to measure, record and experiment with our brewing parameters and are thus able to assess what they can and cannot do for a coffee programme. So we set out to test VST baskets in terms of what sort of consistency they produce over a range of extractions, and whether they are as finicky and inconsistent to use as some have claimed.
Testing the VSTs Using Richard Muhl's crazy shot brewing device and a Synesso Sabre in our Victorian Training facility, we set about testing just how consistent VST baskets are and found it was easy to obtain consistency and repeatability in our results by exercising due care and employing repeatable practices.
To put this in context, we need to define exactly what we are testing. Filter baskets act as the environment where it all takes place to produce the filtered, emulsified, diffused beverage we know as espresso coffee. VST baskets are designed with specificity in mind in terms of how much coffee mass we should be dosing, and have filter holes which are sized and distributed specifically to result in a particular extraction yield range of 18 - 22%, across a range of brew ratios when we adjust our grind particle size to match.
"Whuh?" you may exclaim!
Dose mass This is the amount of coffee we use, expressed as weight. VST baskets are designed to work within a 3 - 4 gram range of dose weights and are manufactured in several sizes. Most filter baskets are purposely or inadvertently designed with this attributed, but VSTs also have filter holes which match the target coffee mass and particle size to deliver specific results.
Brew ratio This is the amount of coffee mass that goes into the basket vs. the beverage mass that comes out. For example, a fairly standard espresso shot uses a 1 : 1 ratio. (This is considered to be a ristretto shot by VST standards.) Or you can think of it as 20 grams of coffee mass vs 20 grams of extracted beverage. Different brew ratios will have different levels of concentration or strength.
Yield % This is the total amount of diffused elements obtained from coffee during extraction. Put simply, it is the maximum amount of a coffee's mass which is removable. It's usually around 28%, but we don't want all of that.
Generally with espresso, a reading of the Total Dissolved Solid % (the amount of solids present in our brew) is attained using refractometery. Using the initial dose mass, we can then calculate how much of our coffee's diffusible content has been removed. Historically, a range of 18 - 22% of the coffee mass has been deemed to be the spot to hit in terms of flavour. The TDS % differs depending on how diluted the espresso is, and directly correlates to concentration or strength.
Filter holes Filter baskets have holes which allow brewed liquid to pass through them. The more total surface area these holes provide as an escape route for water, the faster our flow rate will become.
Think of it like this: if we have two filter baskets filled with equal amounts of coffee which are tamped in exactly the same way and one of the baskets has more holes than the other, then in that basket the water will have more chance of escaping during the extraction process, and the overall flow rate of our beverage (weight over time) will increase. If all other parameters are stable, then dose mass, distribution and grind size should be the only factors influencing the amount of beverage mass we achieve over time.
Or not? Judging by the feedback I've heard so far, results are up and down with VSTs. Thankfully, our testing on VSTs shows that stable brewing parameters are very easy to achieve using VSTs. In fact, after using them for a few weeks of training I am more than convinced that they are delivering more consistent results than our previous baskets, not to mention some amazing tasting shots.
In both VIC and WA, we found that keeping the parameters consistent was the key to ensuring they behave in the same way each time we extract. Furthermore, the way we initially dialled in our parameters (in terms of dose volume, mass and particle size) was critical to ensuring that they behaved in a stable fashion.
If the way we set these baskets up determines what sort of results we can attain, then it's crucial we understand what we are looking to achieve.
Filter baskets are just a small part of making espresso coffee. So let's look at some of the brew parameters which are directly affected by a filter basket. Let's put things in context in an unashamedly complex fashion.
Dose mass, volume, headroom and saturation. Simply put, the dose is the mass of coffee we end up with in our portafilter for an extraction. This can be a fairly accurate and repeatable parameter if we weigh it while dialling in the grinder. Also, there are suitable and unsuitable doses for each individual filter basket, a concept which is based on the idea that the relationship between the following parameters is commonly linked:
Ground coffee volume vs. grind particle size The finer we grind coffee, the more efficiently it will fit together when compressed and the less space it will take up. Put another way, if we are measuring and setting the dose by weight, this means that when we adjust our grind finer, the level at which the coffee sits in the basket will drop even though the weight of coffee has not changed. Of course, it works in the opposite way if we are grinding coarser. We principally use the size of our grinds to affect the rate at which our espresso flows. However, the same extraction process is also affected by the depth at which coffee sits in a portafilter due to saturation and headroom (see below).
So why does this matter? Well, water behaves in interesting ways during the extraction process and those effects become fairly evident when we analyse the effects of headroom.
Headroom Headroom is the space above where the coffee sits level in the basket. Headroom ultimately dictates how much or little space coffee has to expand during the extraction process.
Coffee tends to expand considerably when it is extracting, and it needs a little space to do so without impacting or restricting the water flow. If we use too much coffee when dosing, then we limit the space that coffee can expand in, which conversely affects how evenly the saturation process (see ‘Saturation and Resistance' below) can occur. If we use too little, we allow the coffee to expand to a point where water can easily bypass the grounds below, also affecting how evenly water flows throughout the extraction process.
This means that for every filter basket, there is a volume of coffee which will allow a homogenous saturation, and a matching grind setting which will provide us with extraction flow rates and yields that are most desirable. There is a tipping point when saturation becomes inconsistent, but it's also worth noting that a range of dose volumes work well for a given basket.
Saturation and resistance Saturation and resistance are other factors which are affected by the dose mass, volume and grind. Within the extraction process, water generally travels around the edges of the basket and eventually makes its way through the centre of the shot as resistance is built up from extraction pressure and the coffee itself. The more depth we create from our dose volume, the more we exaggerate this effect; the less depth we create, the faster this process can occur.
The best way to use VSTs If you've been following the gist of this article so far, you can probably tell I'm in favour of VST baskets. My only advice would be to experiment when setting them up to get optimal results.
We've found that VST baskets produce impressive results in terms of repeatability, attainability and flavour, but it all comes back to our ability to adjust and refine in order to achieve these results. The variables involved in espresso can often outweigh the ease of practice: if a filter basket can help us attain specificity and repeatability, then using them makes our goal of producing amazing espresso easier to accomplish.