Summer butter essentially just means butter made in the summer. Winter butter is pale, because the cows are fed hay at that time of the year (though colouring such as annatto is added to the butter to compensate for that.) Summer Butter naturally has more colour in it, because the cows are eating fresh vegetation with carotene and chlorophyll in it.
The colour of butter is no indication of quality, one way or the other. Homemade butter and artisanal butter made in the summer, however, may be somewhat better for you than winter butter, owing to higher levels of carotene in it. Commercial butter, however, adds carotene in the winter to ensure that the nutritional value is consistent year-round.
Summer Butter is also naturally harder than winter butter. To ensure year-round uniformity, butter is “fractionated” — the butterfat is separated into harder and softer portions, then recombined at a standard ratio.
Australian, New Zealand and California butters are essentially always Summer Butters, because their cows graze outside the year round in pastures. In Australia, artificial colouring, such as is used in North America and in Europe, is not needed or used in the butter.
Some consider Summer Butter the best butter for salting.
Shortbread makers swear by summer butter for making shortbread.
Some people didn’t bother making butter during the summer. Butter is made from cream, and the process for getting cream was to leave milk sitting out in a dish overnight to allow the cream to rise to the top, to be collected. In hot summers, though, the milk set out might just spoil overnight. And even if it didn’t and you could make butter, without access to ice or cool storage places like milk cellars, Summer Butter — even salted — could turn into what people called “axle grease.” So instead, you’d use butter that had been made in cooler seasons, and preserved.
Some who made butter on a large scale for trade and sale would construct “milk cellars” buried in the ground that would help to keep the butter and the milk cool. Summer Butter was always cheapest to buy, because it was so abundant. Consequently, to get a better price, many butter makers would salt the butter and store it in their milk cellars for sale in the fall or winter when it would fetch more money.
In the EU (as of 2005), farmers are given subsidies to store summer butter and sell it in the winter. If they sell it in the summer when it is plentiful, it would depress summer prices. Also, selling it in the winter helps to even out winter prices for consumers.
Some people, though, used to swear that not even Summer Butter could beat spring butter: that spring butter, in fact, was the tastiest and the best coloured.
Literature & Lore
“It might be of interest to farmers and others that those people recognized that the butter coming from the milk coming from the early and rapidly growing grass was considered superior to butter at any other time of the year. In effect the cows from the Loetschental valley [Ed.: in Switzerland] had a much longer spell of early summer grass than farms most everywhere else, as they grazed higher and higher up the mountains as the snow cover retreated with the warmer days of summer. Chemical analysis of that butter revealed that it was especially rich in vitamin D which is essential for calcium absorption, and as is commonly known that contributes to good and strong teeth and bones, plus other benefits to the body.
Upon telling this to someone recently he said he knows of a Nova Scotia farmer who always buys early summer butter and stores it in his freezer for his family, as he knew that butter was better than butter at any other time of the year. I read elsewhere that some of this early butter was saved for the pregnant women and the young children in order to get the children off to a good start.”
— Chris Mermuys, The Mother of Invention: A Reader Writes and Cites. In Island Farmer. Montague, Prince Edward Island, Canada. 11 January 2006.
Something could be said to as be “soft as summer butter”, alluding to butter melting in the heat.
Something could also be said to be as “yellow as summer butter”, alluding to the pronounced yellow colour.