Making Sourdough in Winter

Winter temperatures are often a struggle point for home fermenters, and this is true across all ferments – from sourdough bread to bottles of kombucha. Much like us, our little fermentation microbial communities are happier in summertime, and a bit more sluggish and sleepier when its chilly outside. 

Although sourdough thrives in a toasty summer temperature, there are tips and tricks to keep it warm and happy enough even in a cool winter home kitchen. Let’s dig into this topic in a bit more detail so you can look after your sourdough starters and bake fluffy loaves year-round.

Why is my sourdough starter not rising in winter?

Sourdough communities are made up of more than 50 different species of lactic acid bacteria, and up to 20 different species of yeasts. They effectively constitute a little village of their own right, living on your kitchen bench. 

When winter arrives, all animals tend to slow down in the cooler temperatures, regardless of whether that animal is a mammal, reptile, or even a sourdough microbial community. So, when the ambient temperature of your kitchen falls below 18-19°C, your sourdough will also slow down, as the microbes want to conserve their energy. They won’t completely stop or die, but they will take longer to rise, they will peak less dramatically, and they might sit looking quite flat for many more hours than you expect them to. 

Caring for sourdough in a winter kitchen isn’t overly hard or complicated. It simply means that we need to adjust a few things like the temperature of the sourdough container, the timing of feeding with flour and water, the temperature of water additions, and the amount of food they get each feeding cycle.

What is the ideal temperature for a sourdough starter?

From our experience at Symbiota, these are the key temperature points that signify changed behaviour in sourdough activity:

• Below 18°C:

Very sluggish, very inactive, hard to achieve bubbles or leavening. 

Loaves struggle to attain a sour flavour or vibrance as the microbial community changes, with yeasts failing to thrive in the colder temperatures.

• 18°C - 20°C:

A noticeable slow down, bubbles and leavening occurs but is later than expected. Some palates may detect less sour flavours in the baked sourdough loaves.

• 21°C - 26°C:

The sweet spot, where starters and loaves are happily peaking to bubbles and rising. 

There is a balanced sour flavour that results in the final sourdough loaves.

• 26°C - 29°C:

Starters peak faster than expected, with lots of thin bubbles. 

Loaves reach peak leavening faster than expected and may sink before baking. 

Some palates may detect stronger sour flavours in the baked sourdough loaves.

• Above 30°C:

Starters peak really quickly and become frothy.

Regular starter feeding routines can’t cope with the hungry demands of the starter. 

Loaves are too sour in taste as the microbial community changes, with yeasts becoming more dominant than lactic acid bacteria.

Think of your sourdough as a friend who loves a breeze-free and sunny spring day. They’re not fond of winter sports, and they’re not keen to go for a sauna either. 

How do I keep my sourdough starter warm in a cold kitchen?

There are several options to keep your sourdough starter warm in a winter kitchen, and some options are easier and cheaper to achieve than others. It all depends on your budget and motivation levels, how cool the temperatures are in your kitchen, and what types of options you might be willing to consider.

We’ve put together our best Symbiota recommended options that will address most issues, and we’ve organised the list for the different options that you may want to consider:

All of these options can be used for keeping your sourdough starter warm in winter, and for maintaining sufficient temperature to successfully leaven a loaf of bread during winter. 

Can I use a heat mat for my sourdough starter?

A heat mat is a great low-cost investment for home fermenters who want to maintain a steady sourdough supply for their families. A low-setting heat mat is affordable to buy and cheap to run. We have a great quality heat mat at an affordable price available on the Symbiota website. 

A couple of our top tips for using a heat mat include:

1. In cooler weather, consider using a heat mat within an enclosed, lined container for maximum efficiency.
2. Use a thermometer as well to regularly check the core temperature of the sourdough starter or dough under fermentation, so that you gain a full understanding of how the temperature settings relate to actual temperature of your ferment.

Should I change my feeding ratio in cold weather?

Because sourdough starters and loaves tend to ferment more slowly in cooler weather, a reasonable consideration is to reduce the frequency of feeds, or to use more starter in the feeding cycle. 

Whether you elect to change the feeding ratio in cold weather will really depend on how cool your kitchen actually is, whether you are able to take other steps to change the temperature of the fermentation space (as above), and what your level of commitment is for making seasonal changes to recipes that may well be committed to your memory. 

If you do decide to alter feeding ratios, here are our top tips to consider:

• Use an ambient temperature thermometer to learn the actual temperature of your kitchen fermentation space, and how the temperature alters between day and night, so that you have the right numbers in mind.
• Watch how long the starter is taking to reach the peak in the cooler weather, before making any adjustments.
• Changes to consider (select one change only):

• • Allow 1-2 extra days in between feeds without changing the recipe

  • Change the feeding recipe ratio from 1:1:1 (starter: flour: water) to 2:1:1

Be confident to use your sense rather than using the clock or a calculator. How does your sourdough smell? How slow are the usual behaviours of bubbling and rising? What does your best understanding of your starter behaviour and the kitchen temperature indicate to you to be the best steps for change?

How long should my starter take to double in winter?

This is a difficult question to answer with a specific given number, as the vibrancy of a starter really does depend on the regularity of care, temperature gradients, feeding cycles, ingredient quality, water quality, and the composition of the probiotic microbes within the starter. 

Most healthy and regularly fed sourdough starters will double in size by season as follows:

• Warm Seasons: 4-8 hours
• Cool Seasons:  8-12 hours

If your sourdough starter has attained a doubling in size within 12 hours in a cool kitchen, it is most likely vibrant enough to bake a successful sourdough loaf. If the starter is taking longer than this to double in size, consider changing the dough temperature conditions or feeding schedules to support better sourdough health.

Why does my starter smell like acetone when it’s cold?

If a sharp, acrid, acetone-like smell is evident from your sourdough starter, it usually means that the microbial communities are hungry. In practical terms, they have run out of food and are now producing greater quantities of alcohols (from the yeasts) and acids (from the lactic acid bacteria) which is causing the acetone-like aromas.

Colder weather and colder core dough temperatures will slow down the feeding activity of the microbial communities in your sourdough starter, and it may have been left too long in between feeds. There are a couple of solutions:

• Adjust the feeding ratio to be smaller and more frequent
• Increase the temperature during the feeding period

After 2-3 feeding cycles that are more in balance with temperature, or with slightly warmer temperatures applied, the smell of the sourdough starter will shift back to the pleasantly sour aroma that you know and trust.

How do I adjust bulk fermentation time in winter?

Here is a good place to revisit your knowledge about bulk fermentation – this is the period of bread development where the dough is developing strength, gluten is stretching, and flavour is slowly souring. Here are our top tips for making small adjustments for bulk fermentation to be as successful as possible in cooler kitchen temperatures:

• Increase the expected time of bulk fermentation to 6-10 hours
• Use the appearance of the dough as your best indicator, not the clock
• Look for the key leavening measures of rise, jiggle and bounce back
• Longer bulk fermentation times are OK as long as the dough doesn’t collapse or become overly acidic
• Alter the dough temperature conditions for bulk fermentation using one of the methods described here so that you can keep to the regular expected bulk fermentation times of between 4-6 hours

What water temperature should I use for sourdough in winter?

Using a warm water when mixing for sourdough starter feeding and dough formation is another great opportunity to raise the core temperature of the microbial community. Care must be taken to make sure that water isn’t hot, which could damage the microbes. 

Our best advice is:

• Use water that is comfortably warm against your hands, like a soothing bath 
• Avoid a hot tap or hot dishes temperature of water
• If you are using a thermometer for accuracy, use water that is 28-30°C 

Can I use warmer water to speed up fermentation?

It would not be effective to use warm water alone to support your sourdough in a winter cool kitchen. This is because the temperature gradients that the microbes experience between initial warm ingredients that then cool to ambient winter temperatures will be stressful.

For these reasons, our best advice is to mix warm water additions into the ingredients quickly and thoroughly and then pair the warm water addition with a warm proofing spot, or insulated container. This allows for a gentle and steady fermentation supportive warmth, rather than relying on warm water alone.

Why is my sourdough dough not rising in winter?

There are three key reasons why sourdough may be failing to rise as expected during winter:

1. Cool core temperatures are slowing down the yeast activity
2. The sourdough starter was too cool to reach peak activity before mixing the dough
3. The dough was not given sufficient time to proof in cooler temperatures

When making sourdough in winter, there are several points to consider before deciding on which solutions are appropriate for your home kitchen (as described above):

1. Consider the different ways of increasing fermentation temperatures 
2. Consider the different ways of adjusting ingredient feeding schedules
3. Regardless, always make certain that a sourdough starter doubles before use
4. Use your senses to extend the bulk fermentation and proofing times accordingly

Take time to really get to know your sourdough starter, your kitchen temperatures across the seasons, the warm and draught free spots in your home, how to hand water temperature additions, and consider how important it is to you before investing in additional equipment. 

As always – our best advice is to trust your senses. Fermentation is different in every kitchen. It changes with the ingredients you select, the season you are in, and the starters that you began your fermentation journey with. With time and practice, your confidence and knowledge will develop, and you’ll become the expert for your very own fermentation practices. Alongside the critical scientific knowledge of fermentation lies a human art form in understanding the microbial village you are working with, the seasons you are in, and just the way that you like things to be. Confidence is key.

Should I increase the amount of starter in my recipe during winter?

One of the options to manage the slower fermentation changes that occur during winter is to use a slightly higher percentage of sourdough starter in both feeding and dough development. It is important to recognise though, that this isn’t the best single solution to be selected for several reasons:

• Using more starter in recipes will speed up fermentation, but it will come at a cost

• • More starter in a feeding cycle will increase acidity

  • More starter in a sourdough loaf will increase flavour intensity

In a pinch, possibly at the beginning of the cooling season, making the adjustment to increase the amount of starter might be the first option you choose. Our best recommendation though is that when this occurs, it is a key indicator that it is time to look at making longer-term seasonal changes for the duration of the upcoming cooler weather. Check the methods we’ve described above for managing warmer fermentation temperatures in winter, and/or adjusting fermentation recipes and timing schedules for the wintertime.

Where is the best place to proof sourdough in a cold house?

The best sourdough proofing places are warm, stable in temperature, and free from draughts. We have put together a table of options above that give specific detail on the different options that we recommend as best. But in general terms where little to no changes or purchases are required, our best tips for proofing places in a cold house are:

• In a container withing a hot water cupboard
• Inside a barely heated oven with the light on
• Inside a microwave oven with a hot water bottle

We like these three options the best because they are generally achievable in most homes with no additional purchases required, and each option removes the risk of any unwanted cool draughts.

How cold is too cold for sourdough?

Sourdough starters and loaves can reach complete fermentation in cool room temperatures that are as low as 15-18°C. But the process will be markedly slower at every step – from starter to bulk fermentation to final proofing the dough. You may find that one loaf could take several days to become a hot, buttered reality!

In our experience, temperatures that are below 10°C become really difficult to achieve a balanced loaf of sourdough. Fermentation times will be tricky to achieve in a balanced way, starters and doughs risk failing to ferment at all, or becoming too acidic depending on what feeding recipe changes may have been made.

If your fermentation temperatures are below 10°C and approaching that of a fridge, fermentation will be effectively stalled. The sourdough starter and doughs will be more in a resting state than an actively working state. 

In kitchens that are as cool as this, we highly recommend taking measures to increase the fermentation temperatures first and foremost, before making changes to recipe formulations or fermentation timings. Consider putting into practice one or more of the fermentation temperature adjustment methods that we have described above.

Can I use my oven light to proof sourdough in a cold house?

Using an oven light in a barely warmed and closed oven is a common home trick for sourdough bakers, and this is a method that many people do use to bulk ferment and proof sourdough. We have some key tips to make sure that this method works as best as possible for everyone:

• Always make sure the oven is off before placing a ferment inside, except for the light.
• Use a thermometer to check the actual temperature within the oven first.
• If too warm, slightly open the door, then continue regular temperature monitoring.
• If you do preheat the oven lightly first, make sure to use the below 50°C setting and turn the oven off once attained. Then use the thermometer to monitor that the temperature reduces to 30°C before placing any ferments into the oven.

Our biggest tip is to set a timer to remind you that there are ferments in the oven, so you don’t forget. Out of sight, out of mind does happen. Collapsed sourdoughs have been forgotten in ovens, or ovens have been pre-heated by someone else without checking inside first! These are the types of sourdough tragedies that you definitely want to avoid, especially after you’ve invested hours of extra winter care and attention to getting the best loaf possible.

Is a Hot Water Cupboard good for sourdough proofing?

A hot water cupboard is a great option for proofing the dough in winter, as long as some checks are put in place:

• Remember that heat rises, so the warmest spots will be high in the cupboard.
• Check where the temperatures are in the best range using a handheld thermometer.
• Place the proofing dough into an enclosed container to avoid any spills or contamination.
• Keep the door closed to avoid draughts.
• Set a reminder to check the sourdough regularly – out of sight can be out of mind!

Does sourdough taste different in winter?

Sourdough care and sourdough baking is a definitive mix of science and art. When seasonal temperature differences are added to the mix, inevitably the results will bear out in the flavour of loaves. The longer and slower fermentation times of winter often enhances the sourness of a sourdough loaf, and results in a deepening of the general flavours. 

Symbiota’s top tips to make sourdough in winter:

We have covered just about everything you need to know for making sourdough in winter. There are a lot of seasonal changes that can be made, and a lot of information to consider. To keep it simple, here are our absolute best tips for anyone wanting to make sourdough in winter:

1. Know your conditions:

Get to know your sourdough starter and your kitchen temperatures across the seasons. Use a thermometer and your senses together to guide decision making.

2. Prioritise warmth:

Warm and draught free spots are critical, and there are several ways to achieve these in winter. Check our table above to help select methods that are best for your situation and preferences.

3. Extend fermentation times:

Be confident in your knowledge of your sourdough to make an educated decision to extend fermentation times. Then be confident to use your senses to decide when to stop fermentation to avoid collapsed doughs or overly sour loaves.