Introduction

This page gives additional information about some of the science that underpins the Encapsulated Pour-Over (EPO) coffee brewing method, used in the Simple Smart Coffee Brewer.

We have not repeated the detailed arguments and evidence that is available in the sources we quote.

Coffee Expansion

Coffee grounds swell relatively quickly when immersed in hot water. After about 30 seconds they will have reach 60%-80% of their final unrestrained size.

In a 2020 research paper it was reported that the diameter of coffee grounds increases by about 15% (see Swelling properties of roasted coffee particles - Verena Bernadette Hargarten, Michael Kuhn, Heiko Briesen). As the volume is proportional to the cube of the diameter, this means that coffee will expand to about 150% of its original volume in hot water, if not restrained.

If the coffee is encapsulated within a space that is less than 1.5 times the volume of the dry coffee (as it is in the SSC Brewer) it will expand to effectively fill the entire space available. The expanding coffee will create a uniformly dense coffee bed.

This gives the ideal uniform and flat coffee bed for the most even coffee extraction (see ‘Benefits of Flat-bed Extraction’ below).

The encapsulation of the coffee removes the issues associated with channeling in a “loose bed of coffee” (see The Physics of Filter Coffee, p101 - referred to as ‘TPofC’ below). See ‘Filter Plate Design’ below, for more details.

Also any micro channels that may start to be opened by carbon dioxide escaping from the ground coffee are also quickly closed off by the expanding coffee.

Coffee As the Primary Filter

As Jonathan Gagne has pointed out (TPofC, p105), “for gravity-driven brews, the bed of the coffee is our best filter to retain fines and produce a clean cup.”

The SSC Brewer has a two-stage filter process. The encapsulated coffee bed in the filter body serves as the primary filter, which controls flow-rate and therefore the extraction of the coffee flavors. Users can then apply a secondary filter, if they wish to, using the included fine-mesh metal filter or a paper filter to modify the ‘texture’ and ‘cleanliness’ of the coffee to suit their preferences. The paper filter will remove many of the coffee oils that are extracted as an emulsion rather than being dissolved by the water.

This design removes any issues associated with ‘clogging’ of the filter, as if a secondary metal or paper filter is used it does not affect the the flow-rate (unless the wrong type of paper filter is used - see FAQs).

A tertiary (or third) filter can be added by staking two of the Adaptors with paper filters in them. This is useful for dealing with ‘clogging’ or ‘choking’ of the paper filter if the ground coffee contains too many fines (or if you want an exceptionally ‘clean’ brew!).

Benefits of Flat-bed Extraction

In TPoC p103, Gagne highlights that the ideal coffee bed is a flat cylindrical one (as opposed to a cone shape) with no agitation and no water bypass. This is because it “produces an extraction that is more even … because the velocity of water remains constant across it”. This is exactly the what the SSC Brewer delivers.

Filter Plate Design

The Filter Plate performs two roles.

Firstly, it is carefully designed to fit snuggly into the Filter Body, so that the coffee is encapsulated. The plate is made of a lighter gauge steel than the body, to provide the necessary flexibility to seal the profile and so that it expands slightly faster than the filter body - due to thermal effects - enhancing the seal.

Secondly, as the water is poured onto the plate - not directly onto the coffee - it removes the risk of the water digging “a hollow at the surface of a coffee bed” which can open channels in traditional pour-over methods. This mean we can use a shallow coffee bed, not needing the “3 centimeters in depth” attributed to Scott Rao (TPofC, p102).

With its shallow coffee bed - it will have a thickness of approximately 0.7 centimeters - the SSC Brewer removes all the issues associated with unevenness of extraction through layers the coffee bed referred to in TPofC p102-3.

Preinfusion Processes (The ‘Bloom’)

The preinfusion - or ‘bloom’ - phase typical of most pour-over methods has two primary objectives:

1. To get the coffee uniformly wet before the main volume of water passes through This is to avoid overextraction through channels where the coffee is wetter (with lower hydrostatic resistance) as water passes more easily through this than drier areas.

2. To prevent carbon dioxide escaping from the coffee grounds opening micro-channels in the coffee bed. This again leads to localized over-extraction.

Neither of these are an issue for the SSC Brewer.

As the coffee bed is uniformly deep (and relatively shallow) and because the water is poured onto the filter plate - not the coffee directly - water is uniformly distributed across the entire coffee bed. The coffee is always uniformly wet within the first few seconds of the pour.

As the coffee is expanding during the brew (it gets to about 70% of its total expansion within 30 seconds and is fully expanded after 4 minutes) any micro-channels opened by escaping gases are always closed off.

There is no need for a preinfusion phase with the SSC Brewer

Temperature Issues

The use of a Lid on the SSC Brewer has two functions. It enables the user to lift the filter when it is still hot. Secondly, it keeps the water at a more constant temperature while the brew is happening. Tests have shown that the water temperature is approximately 5°F higher at the end of the brew when the lid is used.

As the capillary action that extracts compounds from the ground coffee is more effective at higher temperatures, this might have a positive slight impact on the extraction, but this has not been tested.

There is also no need to preheat the brewer as it is of modest mass and made from stainless steel with has a relatively low thermal capacity (which indicates how much energy is required to heat it up). Our tests have shown that if you pour water that has just boiled in a single pour (as recommended) the initial brewing temperature of the water will be around 200-203°F (94-95°C) which is in the range considered optimum.

Rinse Paper Filter

We do not believe that it is necessary to rise the paper filter to remove potential papery taste.

In our tests, it has not been possible to determine whether or not the paper filter has been rinsed. The SSC Filters are very small and made of bleached paper.