Health Care Market Research

All Important News



科学者らは、コーヒー豆をより細かく挽くと、抽出が不均一になり、エスプレッソが弱くなってしまうことを発見しました。 彼らは、単純な数学モデルを使用してコーヒーを 2 つの領域に分割し、不均一な流れが抽出プロセスにどのような影響を与えるかを調べました。 この不均一な流れはコーヒーベッドのさまざまな部分にわたって持続し、コーヒーの味に影響を与えました。 不均一な抽出を理解して防止することで、コーヒーの淹れ方を改善し、より効率的なコーヒーの使用により経済的な節約を達成できる可能性があります。


ハダースフィールド大学の研究者らは、細かく挽いた豆を使用すると、エスプレッソ抽出で不均一な抽出がコーヒーの味を弱める原因となることを発見しました。 この現象を理解して防止することで、コーヒーの味を改善し、より効率的なコーヒーの使用により経済的節約が可能になる可能性があります。

エスプレッソコーヒーは、まず焙煎したコーヒー豆を粒状に粉砕して淹れます。 次に、熱水が高圧でコーヒー粒の床を通過し、コーヒー粒の可溶性成分が水に溶解し(抽出)、エスプレッソが生成されます。

2020年、研究者らはコーヒー豆を細かく挽くとエスプレッソが弱くなることを発見した。 この直観に反する実験結果は、何らかの理由でコーヒーベッド内にコーヒーの抽出量が少ない、またはまったく抽出されない領域が存在する場合には意味があります。 この抽出ムラは、コーヒーを細かく挽くとさらに顕著になります。

Coffee Flow Instability

In this figure, Q is the rate of flow, epsilon is the porosity (which increases as coffee is extracted), and c is the concentration of dissolved coffee (a measure of the strength of the espresso). Credit: W.T. Lee, A. Smith, and A. Arshad

One of the regions in the model system hosted more tightly packed coffee than the other, which caused an initial disparity in flow resistance because water flows more quickly through more tightly packed grains. The extraction of coffee decreased the flow resistance further, as coffee grains lose about 20% to 25% of their mass during the process.

“Our model shows that flow and extraction widened the initial disparity in flow between the two regions due to a positive feedback loop, in which more flow leads to more extraction, which in turn reduces resistance and leads to more flow,” said co-author William Lee. “This effect appears to always be active, and it isn’t until one of the regions has all of its soluble coffee extracted that we see the experimentally observed decrease in extraction with decreasing grind size.”

The researchers were surprised to find the model always predicts uneven flow across different parts of the coffee bed.

“This is important because the taste of the coffee depends on the level of extraction,” said Lee. “Too little extraction and the taste of the coffee is what experts call ‘underdeveloped,’ or as I describe it: smoky water. Too much extraction and the coffee tastes very bitter. These results suggest that even if it looks like the overall extraction is at the right level, it might be due to a mixture of underdeveloped and bitter coffee.”

Understanding the origin of uneven extraction and avoiding or preventing it could enable better brews and substantial financial savings by using coffee more efficiently.

“Our next step is to make the model more realistic to see if we can obtain more detailed insights into this confusing phenomenon,” said Lee. “Once this is achieved, we can start to think about whether it is possible to make changes to the way espresso coffee is brewed to reduce the amount of uneven extraction.”

Reference: “Uneven extraction in coffee brewing” by W. T. Lee, A. Smith and A. Arshad, 9 May 2023, Physics of Fluids.
DOI: 10.1063/5.0138998

Source link