Professional coffee roasting | Evolution of carbon dioxide and moisture during bean roasting

Professional barista communication, please pay attention to coffee workshop (Weixin Official Accounts cafe_style)

I accidentally read a paper written by R. Mr Geiger's paper examines in detail the moisture and carbon dioxide produced during coffee roasting, and some of its conclusions are a shock. Although the lab heating rhythm is far from our usual practice, understanding these concepts should play a role in understanding future baking, and the key points are summarized here.

First of all, I will explain some nouns and test conditions:

HTST (High temperature short time)

LTLT (Low temperature long time)

The L* value of the two baking methods was consistent, both were 22~23

HTST: 260 degrees hot wind, 170 seconds, wind speed 3.007 m/s

LTLT: 228 ° C hot wind, 720 seconds, wind speed 2.037 m/s

The bean temperature mentioned here is the bean core temperature measured by drilling

The moisture content of raw beans is 8.3%.

Raw beans for measuring chemical reaction water, pre-baked to moisture content of 1.1%

The moisture content of coffee is obtained by dry weighing

It's customary to calculate the weight loss rate of baked beans, but this table not only describes the proportional components, but also unexpected information.

Baking evaporates more moisture than it would otherwise.

The excess water represents chemical reaction water.

Baking emits a low percentage of carbon dioxide.

It emits more carbon dioxide when stored

Although HTST evaporates less water via baking than LTLT, it is estimated that the cooling process evaporates 1.6 g of water, so that the final weight loss of the two is still very close (15.38 g vs. 15.86 g).

These estimates are derived by linearly extending the cumulative evaporation rate of CO2/H2O for 20 seconds.

The difference in weight loss data between the two methods (On-line/calculated vs. Gravimetric) may be due to the inability of the first method to measure e.g. tipping and volatile gases other than CO2/H2O. In addition, measurement errors of gas flow rate, volatile concentration and so on are also one of the reasons.

Relationship between temperature, moisture content, baking weight loss and time of beans

HTST, two curves and time are almost linear

LTLT, two curves and time are approximately exponential

The overall change of coffee beans is mainly determined by the roasting temperature

HTST at 100 seconds, the temperature of beans about 220 ℃, weight loss> 8%, moisture content