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Thermal shock usually describes hot-water rinsing followed by cold water after fermentation. Some lot descriptions give its purpose as encouraging uptake of fermentation compounds and stopping fermentation, although the mechanism needs further research. This stage can accompany anaerobic fermentation and washed, natural, or honey processing; terminology and conditions are not fully standardized.
Thermal shock usually describes rinsing coffee with hot water and then cold water after fermentation. It is a relatively recent processing term, often listed alongside anaerobic fermentation.
Coffee Review describes two Colombian microlots rinsed with hot and cold water after fermentation, with the stated purpose of encouraging uptake of fermentation metabolites and stopping fermentation. One finishes as washed parchment; the other uses wine yeast and continues through a natural process. In these examples, thermal shock identifies the temperature-treatment stage within the longer process.
Perfect Daily Grind records Diego Bermudez’s process using water around 40°C followed immediately by water around 12°C. These settings describe that example; other mills may choose different temperatures and incorporate the treatment into their own processing sequences.
Anaerobic usually means fermentation in a sealed bag or tank that limits incoming oxygen, as explained in anaerobic processing.
Thermal shock focuses on an abrupt temperature change. Coffee Review places the hot and cold rinses after fermentation, while Black & White Coffee Roasters likewise describes it as one step within a longer fermentation process.
Both can form part of the same sequence. Coffee Review’s examples include ozone sanitation, two fermentation stages, and then thermal shock; some lots also use lactic cultures or wine yeast.
Black & White proposes that heat opens seed pores to admit esters from the fermentation liquid, then cold contracts the pores and retains those compounds. Rapid heating and cooling might also inhibit enzymatic activity, as in vegetable blanching. The author notes that the mechanism still requires research: hot water followed by cold water describes the sequence, while the explanation involving pores and compound uptake remains provisional.
A conventional washed process uses water to loosen and remove mucilage before drying. The thermal-shock accounts above instead emphasize deliberately changing temperature with the aim of stopping fermentation at the mill’s chosen point.
Perfect Daily Grind mentions that experimental processes keep multiplying, that the industry has no standard names for them, and that many roasters have never seen the work at origin. Roland Horne of WatchHouse, quoted there, says the lack of naming standards leaves little agreement on what the words actually mean.
On a bag, thermal shock points to a hot-then-cold treatment around fermentation, with temperatures and durations that need to be checked in the lot description. Black & White also mentions a less common use before depulping. The coffee still needs drying and may finish through washed, natural, or honey processing.
Some tasting reports describe greater aroma and fuller texture, sometimes with distinct fruit or fermentation character. These observations do not guarantee better coffee or establish that process character will obscure the origin. Production volumes are usually much smaller than for conventional washed coffee, and the label appears often on experimental Colombian microlots.
They describe different stages. Anaerobic usually refers to fermentation in a sealed, low-oxygen environment, while thermal shock commonly involves hot water followed by cold water after fermentation. A bag may list both.
Some tasting reports describe greater aroma and fuller texture, but processing conditions, timing, and drying all affect the result. Thermal shock can accompany washed or natural processing, and its name alone cannot establish quality.
The sources describe rinsing during processing. Perfect Daily Grind's example uses water around 40°C followed by water around 12°C, but those settings are not universal; the individual lot description provides the relevant temperatures.
Enzyme processing adds pectinase to break down mucilage, while thermal shock uses a temperature change. They may occur at different stages of the same lot. Adding enzymes also differs from yeast inoculation, as explained in the enzyme-processing article.
The name shows up often on Colombian experimental microlots. It is not Colombia's national process, and most Colombian coffee is still conventionally washed.