Botanically Brewed Mint Lemonade

Sugar is hygroscopic. It pulls water and oil out of broken oil glands in the coloured part of the peel. The sugar crystals hold the oil on a large surface. The lemon juice then carries the oil into the drink.

Lemon oil is mostly limonene. The smell that reads as lemon comes from citral (geranial and neral). Citral is only a few percent of the oil.

The white pith contains bitter limonoids and flavanones. A Y-peeler keeps most of the pith out.

Citral is not stable in acid. It slowly cyclises and oxidises. The products, such as p-cymene and p-methylacetophenone, smell flat and medicinal. This sets the drinking window of 1 week. Commercial lemonades use stabilised flavourings and ascorbic acid to slow it. The pH is estimated. Nobody measured it.

Spearmint gets most of its aroma from (R)-(−)-carvone. The mirror-image molecule, (S)-(+)-carvone, smells of caraway.

The oil sits in peltate glandular trichomes. These are small oil sacs on the surface of the leaf. A slap breaks some of them. A blender breaks all of them. Blending is what makes the mint strong.

Broken leaf cells release enzymes. Lipoxygenase turns leaf lipids into green-leaf volatiles such as cis-3-hexenal. These smell of cut grass. Polyphenol oxidase makes the leaf brown.

A 10-second blanch denatures both enzymes before the blender breaks the cells. Carvone and menthol boil above 200 °C, so the short blanch loses little aroma. The ice water stops the cooking.

An unblanched leaf must not be squeezed or muddled for the same reason.

Acid replaces the magnesium in chlorophyll with hydrogen. This makes pheophytin, which is olive-brown. Blanching does not stop this. Over some days in the bottle, the colour goes from green to khaki. The taste does not change.

Menthol activates TRPM8, the cold receptor in the mouth and nose. The brain reads the cold as intensity. Spearmint contains little menthol. One part peppermint to three parts spearmint adds the cold without a toothpaste taste.

Wild yeasts and lactic acid bacteria live on the skin of fresh ginger. Do not peel it. The daily sugar feeds the organisms that ferment.

Yeast makes CO2 and ethanol. Lactic acid bacteria add a light sour note under the lemon.

The pear juice gives nutrients that sugar alone does not give. Fentimans also puts pear juice in its ginger ferment.

Yeast activity is highest 6–12 hours after a feed. The lemonade base is very acidic: estimated pH 2.6–2.9, not measured. Acid slows wild yeast. A weak or cold bug can stall for days. A bug at its peak starts the bottles in 2–4 days.

Each gram of sugar that yeast ferments makes about 0.49 g CO2 and 0.51 g ethanol. About 2.5 volumes of CO2 need about 5 g CO2 per litre. That uses about 10 g sugar per litre, or about 20 g in 2 L.

The base starts near 170 g fermentable sugar (8.4%). It ends near 150 g (7.4%). The ethanol is about 0.5–0.7% ABV.

All of these values are calculated. Nobody measured them yet.

CO2 carries aroma out of a liquid when it vents. The bug jar vents, so the mint never goes in it. A closed bottle cannot vent. The gas and the aroma both stay in the lemonade. Brewers add aroma hops after the main fermentation for the same reason.

CO2 dissolves about two times better at 4 °C than at 20 °C. In the fridge, gas moves from the headspace into the liquid. The bubbles become finer, and the bottle gushes less when you open it. The cold also stops the yeast.

Solid particles are nucleation sites. CO2 forms bubbles on them. Pulp in the bottle makes it gush when you open it. Pass the juice through a fine sieve.

Fentimans uses pear juice and glucose syrup. Glucose syrup contains dextrins. They add body with little sweetness.

Pear juice contains sorbitol. Saccharomyces yeast ferments sorbitol poorly, so it can stay in the drink as body. This part is a hypothesis. It is not confirmed.

Berlin tap water is hard. Its bicarbonate neutralises part of the citric acid. The lemonade then tastes less sharp. Filtered water keeps the acid.

Juniper oil is mostly alpha-pinene and myrcene. These are monoterpenes, the same family of molecules as limonene in lemon oil.

Because the molecules are related, the juniper does not taste like a separate flavour. It adds depth and a resin note inside the lemon.

Fentimans puts juniper in Victorian Lemonade for the same effect. In this recipe the juniper goes into the oleo, so the sugar pulls its oil with the lemon oil.

An oleo works for lemon because the peel has large oil glands in a thick, waxy skin. The sugar pulls the oil out slowly and cleanly over 90 minutes.

Mint is different. Its oil sits in small trichomes on a thin, wet leaf. Sugar breaks the trichomes, but in 90 minutes it also bruises the leaf cells. The bruised cells release lipoxygenase and polyphenol oxidase. The result is a grass taste and a brown colour.

Heat is also wrong. A hot steep drives off the aroma and pulls out rosmarinic acid and tannins. The result tastes like mint tea, not fresh mint.

So the mint gets its own process: a short blanch to stop the enzymes, then a hard blend in cold water.