I am embarrassed to admit that many of my early prosphora, and a few of my recent ones, have been too sour. Some people enjoy a tangy sourdough bread for home consumption. However, we should aim to develop the mildest tasting, least sour bread for our holy bread offering.
This blog summarizes how. (Alternatively, you can make prosphora with no sourness, using commercial yeast. See here)
WHAT MAKES SOURDOUGH BREADS SOUR?
The microbes which ferment the starter and dough feed on the carbohydrates. They produce acids, carbon dioxide, alcohol and other byproducts. The lactobacilli produce lactic acid which confers a milder milkier taste. The yeasts produce acetic acid which is more sour. We aim to favour the lactobacilli over the yeasts by manipulating certain factors.
During fermentation of the starter or the dough, the acidity rises gradually and becomes increasingly pronounced the longer it ferments. It becomes very acidic when the microbes have exhausted their food source. Thus we should avoid overly long fermentation times.
Lactobacilli thrive best at around 26 degrees centigrade and with around 100% hydration. Yeasts work best at temperatures both higher and lower than 26C. Yeasts thrive better in mixtures with less water - lower hydrations.
STEPS TO LESSEN SOURNESS
You can probably now begin to predict what we might do to lessen the acidity. From before we create the starter until after the baking there are many factors we can control.
Flours that are wholegrain or stone-ground, favour the yeast microbes (these flours have more of the kind of complex carbs which yeasts love). White flour is best for a milder taste.
"Hard"water slows fermentation and contributes to the acidity.
Adding salt doesn't lessen the production of acids but it helps balance the sour taste in our bread.
Tasting and smelling your starter gives you much valuable information. If it has been stored in the fridge, much of the fermentation has been slowed but it is not stopped. Acidity builds up over time especially in the fridge since the yeasts are favoured at those temperatures.
Knowing when our starter is healthy and vigorous is essential. Using a freshly fed starter at the peak of its microbial activity is imperative.
Low hydration starters become sour faster. It's best to use 100% hydration starter. (equal weight of water to flour)
So, either feed your starter at least second daily or if you store it for many days in the fridge, feed it the night before you plan to make prosphora.
If time permits, give it an extra feed just before using it.
Always try to use the starter when it has risen to just before it doubles it's height. If it rises well beyond this point and begins to deflate, it has already built up acidity and is also less vigorous. After feeding your starter, always either use it (or place it in the fridge for storage) before it has doubled in height. This ensures it has not consumed it's food source nor produced too much acid. It is most vigorous at this point. Using it at the height of its vigour shortens maturation and lessens acidity.
If your fridge-stored starter has become very sour, you can remove much of the acidity by giving it a bath before feeding.
BATHING YOUR STARTER
Place it in water at room temperature for 30 minutes. Stir it very gently and break the mass a little - just enough to get water to the middle of the mass. Don't mash it up. Carefully pour off the bath water using a fine mesh strainer. Repeat the bath process. Then feed your washed starter before use. Weighing it before and after bathing will enable you to factor the correct proportions of water and flour needed to restore it to the desired 100% hydration.
THE DOUGH / MATURATION
Using a small amount of starter means fewer microbes have more work to do. The prosphoro takes longer to rise/mature. As mentioned, it thereby increases acidity. Using a larger proportion of starter to flour will shorten the maturation. But using too much may make the dough too weak to accept and keep the seal impression.
The ideal:- in winter use 10% and in summer 5% of the weight of your flour as the weight of starter. (eg for 1000 gr flour, in winter use 100gr starter and in summer use 50gr of starter).
In winter using water at room temperature is fine, but in summer (over 25C) it is best to use water from the fridge. By the time your kneading, shaping and stamping is finished the dough will be at room temperature.
Very importantly, wherever possible, try to have the dough rise at temperatures close to 26C. In Brisbane most of the year our room temperature is close, but in winter I use some gentle warming. In the image below, see how I use my thermometer with hygrometer in the oven warmed and humidified by way of a dish of boiled water. The prosphora rise at around 26C and only need one or two hot water top-ups throughout the long rise period (5 -7 hours).
Sometimes my schedule demands I store the prepared prosphora in the fridge overnight. I take it out of the fridge when ready to let it rise and then bake the next day.Thankfully, provided I have observed all the points above, this period of refrigeration does not seem to noticeably increase the sourness.
I had always assumed that once a bread was baked, all microbial and chemical activity stopped. However, I was surprised to discover that after baking, the acidity can increase over the next day or two! It seems to be more pronounced if I don't allow the prosphoro to dry properly before sealing it airtight ready for freezing.
Immediately after baking, all my prosphora are cooled slowly under a blanket (6 hours) to prevent a hard crust with contraction cracks. Then they're allowed to dry out for half a day. If they are to be given to church within a day or two, they rest in clean tea towels until church. If they need to be stored for many days before church, I leave them wrapped in a tea towel for 12 -24 hours and then I seal them in white kitchen paper towels then clingwrap - airtight - and store them in the freezer until the day before church.
May God bless your prosphora baking efforts.