SlotCatalog explains: Thunderspin's Bonus in Bonus Feature

With the launch of the Book of Jam slot in October 2021, developer Thunderspin presented its new Bonus in Bonus feature mechanic, which amplifies the experience of a standard Expanding Book-style Free Spins bonus.

Thunderspins Book of Jam


With the Book of Jam slot, developer Thunderspin presented its new title built on the well-known ‘book’ mechanic. However, the studio has gone beyond the boundaries of the classic Book of Dead kind of gameplay. The game still sticks to the popular concept and offers a common Free Spins bonus round with Special Expanding Symbols, but it also has a few tricks of its own.

Widely released in October 2021, Book of Jam combines the popular ‘book’ slot mechanics with Thunderspin’s innovative Bonus in Bonus feature, which provides additional guaranteed rewards. You can win extra prizes on each Free Spins trigger in the Super Bonus Game, where you pick and reveal random bet Multipliers to unlock further stages and win the top prize of 500x your bet.

The idea behind the Book of Jam slot was quite simple - take the beloved ‘book’ Free Spins, but with a huge twist that amplifies the experience. In the world of Book of Dead-inspired slots, Book of Jam by Thunderspin feels like a breath of fresh air. It surely delivers a change with its exciting Bonus in Bonus mechanic, which, true to its name, triggers a new bonus game while you’re already in the bonus game.

In this article, we explain how the Bonus in Bonus feature operates. From A to Z, we will go into detail regarding how to trigger the bonus, how to win and how much you can win in the unique Super Bonus Game feature. Though, before turning to the feature review, we should take a peek under the hood of the Book of Jam slot, which acts as the vehicle for Thunderspin’s new bonus system.

What makes Thunderspin’s Book of Jam slot special?

The ‘book’ slots niche counts hundreds of games, and presenting something new that savvy gamblers haven’t seen before is quite a challenging task. However, the Book of Jam slot sticks out from the crowd at the first sight. It’s not some kind of an Egyptian god called Jam, so we’re not traveling to Egypt this time. Book of Jam utilizes a classic fruit theme and takes players to a gorgeous bloomy garden.

Unlike most ‘book’ slots where book symbols act as both Scatters and Wilds, Book of Jam makes use of separate Wild symbols. Anyway, it’s the Scatter symbols you need to enter the Special Expanding Free Spins, and that’s where you can access the flashy Bonus in Bonus feature.

Book of Jam slot from Thunderspin
Book of Jam Reel Screen

So, what makes the Bonus in Bonus feature so special? First and foremost, instead of getting a retrigger, you proceed to a whole different bonus game, which adds a new layer of excitement to the gameplay. Not only do you get a classic Free Spins round with a randomly chosen special Expanding Symbol, but also a Super Bonus Game with the next level of fun and rewards.

Additionally, that allows players to rack up extra prizes, which can be up to 500x the stake. The Bonus in Bonus mechanic is definitely a refreshment when it comes to ‘book’ online video slots, bringing new experiences and opportunities to win to the genre-loving audience.

How do I trigger the Bonus in Bonus feature?

The Super Bonus Game can be activated only during the Free Spins, so let’s start walking you through the standard bonus. 3 or more Recipe Book symbols are needed to trigger the free games, during which Purple Bonus symbols come into play. The recipe to trigger the Bonus in Bonus feature is simple - collect Purple Bonus symbols to fill the Super Bonus counter, and filling the meter with 5 bonus symbols will unlock the Super Bonus Game.

Super Bonus Game
Super Bonus Game Reel Screen

How to win in the Super Bonus Game?

During the Super Bonus Game, the grid expands to 5x5 in size, and players are presented with 25 symbols to pick from. Abundant in tasty jam jars, the reel action offers you a chance to collect bet Multipliers of up to 500x your stake. Each jar contains either a random Multiplier value or nothing, and you climb the Multiplier ladder, proceeding to the next stage after you pick and guess the Multiplier from the previous stage.

You start from the bottom line, and each correct pick unlocks the next row, or stage. Meanwhile, revealing an empty jar ends the Super Bonus Game and the total prize, equal to the accumulated Multiplier value multiplied by the total bet value. However, the first two picks are risk-free, so a win of at least 25x your bet is guaranteed.

Stage Available Multipliers Number of winning cells
1 10x and 15x 5
2 15x, 20x, 25x, 30x, and 35x 5
3 40x, 45x, and 50x 3
4 75x and 100x 2
5 300x 1

During the first two stages, jars only contain the above-mentioned bet Multiplier values, though, as you proceed further, some jars will contain zero. There are three winning jars on the third stage, while the other two award nothing and end the bonus game. On stages four and five, the number of winning jars is two and one respectively, so pick carefully to reach the top.


What is the Bonus in Bonus feature?

The Bonus in Bonus feature is a new game mechanic from developer Thunderspin, which debuted in the Book of Jam slot in October 2021. The feature allows players to trigger a new bonus game during the Free Spins to win additional prizes.

How can I trigger the Bonus in Bonus feature?

While in the Free Spins, look out for Purple Bonus symbols, which fill the Super Bonus counter on the left of the reels. Once you collect 5 instances and fill the meter, the Super Bonus Game will be activated.

How to win in Thunderspin’s Bonus in Bonus feature?

The bonus plays out on a 5x5 grid, where each row contains five jam jars that can award either a Multiplier or nothing. Players start picking from the bottom row, and guessing the correct jar unlocks the next row.

How much can I win in Book of Jam’s Super Bonus Game?

Each stage contains different bet Multipliers, and the higher the stage, the higher are the bet Multiplier values. The first stage offers Multipliers of up to 15x, while the final one can award a massive 300x Multiplier. The maximum prize you can scoop during the Bonus in Bonus feature is 500x your stake.

Where can I play the Book of Jam slot?

You can play Thunderspin’s Book of Jam for real money at any of the offered casinos that you can find on this page or those listed on the slot’s page.

Can I play the Book of Jam slot for free?

You can try the Book of Jam slot demo for free here at SlotCatalog.

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