Yeast & Fermentation

Is Castle Lager top- or bottom-fermented? It's a lager, so bottom-fermented. The yeast works at roughly 8–12°C (46–54°F), eventually settling at the bottom of the tank and giving the beer a clean, restrained character. Its counterpart is the top-fermented ale, where yeast works at warmer temperatures and produces more pronounced fruit aromas.

Large breweries like Newlands now ferment in sealed stainless steel tanks with computer-controlled cooling. That's essential in warm Cape Town, since without cooling, the yeast would work too hot in summer and throw off flavors that have no place in a pale lager. Afterward, the beer conditions cold for several weeks so it turns out clear and smooth.

Castle Milk Stout is top-fermented. The name can be misleading—there's no milk in the glass, but there is milk sugar, known as lactose. The yeast can't ferment it, so it lingers in the beer as a mild sweetness. Roasted malt adds notes of cocoa and coffee.

The small brewers in Woodstock and Salt River also lean heavily toward top fermentation. An ale takes less time than a lager and is easier to manage in small tanks—a real advantage where space is tight. Some brewhouses occupy converted warehouses, their fermentation tanks gleaming behind glass in the taproom.

In the end, temperature remains a constant concern. A lager needs cold, and cold costs energy in the warm Cape climate. The effort pays off, though, since cold-fermented beers taste clean, and that's exactly what drinkers expect.