Posts Tagged ‘tea’

TGRWT #19: Tomato and black tea

Monday, September 7th, 2009

tgrwt-19

This month’s round of TGRWT is hosted by Pablo over at Medellitin, and the foods to pair this time are tomato and black tea. As always you can find instructions on how to participate in the announcement post. If you are new to TGRWT (which stands for They Go Really Well Together), check out the round-ups of the previous 18 rounds! And if you are chemically inclined, you may want to read on to learn more about the compounds behind this months pairing.
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Wonders of extraction: Water

Tuesday, June 3rd, 2008


Extraction of peppermint leaves with hot water

Water is a polar molecule, meaning that one end has a small negative charge and the other a small positive charge. Because of this water is a very good solvent for other polar molecules and ions. For instance water is the solvent of choice for substances that provide taste, be it salt, sour, sweet or bitter as these are normally quite polar molecules.

A general rule is that the solubility of molecules and ions increases with the temperature of the water. Extractions are therefore faster if the water is boiling. This is the reason why we use hot water to extract tea leaves or ground coffee beans, even if we want to prepare ice tea or ice coffee. But by lowering the temperature and extending the extraction time we can change the relative proportion of what we extract. It therefore makes perfectly sense that different temperatures are recommended for different types of tea. Using different temperatures for the same kind of tea will of course also influence the flavor profile.

Polar molecules are more easily extracted than non-polar molecules. This is evident if we leave a tea bag for a long time in hot water. The bitter taste is due to the slow extraction of large polyphenol molecules which are less soluble in water. If tea is brewed at a lower temperature, less of the bitter tasting substances will be extracted.

Although water is polar, less polar and even non-polar substances can be extracted with water, especially if the water is boiling hot. You do this every day when prepare coffee. If you take a close look at cup of freshly brewed coffee you can notice small pools of oily substances floating on top of the coffee. The more severe conditions used when extracting coffee to make an espresso ensure that even more oily substances are extracted. Other examples of extraction using water in the kitchen include preparation of stock, soups and gravies.

The principle of extraction is simple, but a number of questions remain largely unexplored with regard to flavor: How do ions affect extraction? What role does pH play? How does temperature influence flavor? There is surprisingly little research on this that includes a sensory evalution.

Drink your tea without milk!

Wednesday, January 10th, 2007

Experimental and clinical studies indicate that tea exerts protection against cardiovascular diseases. However, a group of German researchers (abstract, European Heart Journal 2007, ASAP contents) have found that the beneficial effects of drinking tea may be reduced if milk is added to the tea.

milk drop hits coffee
(Picture by IreneM entiteld “coffee with a “drop” of milk” from DPchallenge – OK, it’s not tea, but I just love this picture!)

By measuring the blood vessel’s ability to expand (and thereby reduce the blood pressure) the researchers found that this ability was improved by tea, but the effect was completely blunted if milk was added to the tea. It was found that the caseins were responsible for the observed inhibition, probably by formation of complexes with catechins. It is believed that catechins (polyphenolic compounds, belong to the group of flavonoids, structure of epicatechin shown below) trigger the release of other active substances that are responsible for the expansion of blood vessels (also known as vasodilation).

epicatechin

The results of this study are not limited to tea, because catechins are found in many other foods, including citrus fruits, wine and chocolate.